Extracted Magnets from Broken iPad Case

This was an aftermarket protective cover case designed to fit 6th generation Apple iPad tablets. Purchased from the lowest bidder on Amazon that day (*) it did its job for several years absorbing abuse until a corner broke off and the case could no longer latch in place. It turned out a case that wouldn’t stay attached was worse than no case at all, as the iPad fell out causing a dent on the back.

While remaining three corners of this case were still attached, they all showed cracks in the plastic. Thus it was retired and replaced with a new case. Before this broken case is sent to landfill, though, I wanted to salvage its embedded magnets. This cover has the option to fold into a stand, held in shape by magnets. Closing the cover is also something detectable by the iPad, so there’s a Hall sensor inside the tablet picking up a precisely located magnet.

Using a screwdriver for its steel shaft, I could feel tugs at several locations indicating a magnet. Given how thin they must be, I expected to find a few tiny slivers of rare-earth magnets. And given the thin fabric construction, I decided to start by cutting an edge with scissors.

First magnet was quickly uncovered.

Pulling on the glued-on fabric, I uncovered the remaining magnets embedded within the first panel. Four small rectangular magnets near the middle of the edge. Surrounded by two larger rectangular magnets on either side. There’s a circular magnet as well, away from the rest. I had only expected one or two magnets, so this is an unexpected bounty.

The magnets weren’t attached to the yellow plastic backing at all, merely held in place by adhesive on either side. They could be peeled off with minimal residue. This is working out really well.

Continued peeling discovered another circular magnet in the middle panel, and another set of rectangular magnets on the third panel that matched the arrangement of magnets in the first panel. Those two arrays of rectangular magnets on outermost edges would implement the fold-into-a-stand function. The two circular magnets don’t line up to each other, I guess they are there for iPad “cover is closed” detection.

I cut into this cover expecting just a magnet or two, so I’m very happy I came out with a stack of 18 little magnets. They are very thin so it should be easy to fit them into places in future projects. In fact, they are so thin I need to worry about protecting them. This material is brittle: I broke that topmost magnet in half when peeling it off the adhesive layer, a lesson warning me to be careful with the rest.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Monoprice 30W Powered Desktop Speakers (605300)

Encouraged by my resurrected Insignia powered subwoofer, I dug up another item from my to-do list. These are Monoprice Pro Audio Series 30W Powered Portable Speakers, item #605300. (No product link as this item has long since been discontinued, though their Powered Desktop Speakers category is still alive and well.) I had bought it for use as my computer desktop speakers and they worked well for a few years before falling silent. Then they sat for many more years in the teardown/repair pile until now.

The two speakers are not symmetrical. One of them have all the equipment and the other is a simple box with drivers. The fancier box (wired up to be the right channel but shown to the left in above picture) has a volume knob and two audio jacks. One jack is an auxiliary input to temporarily replace signals coming in from rear main audio input, and the other a headphone jack we can plug in to temporarily listen to something privately. This latter jack still works: I could hear the audio signal through headphones plugged into this jack, and I can hear loudness changing as I turn the volume knob.

The asymmetry is very visible when looking at the rear of both speakers. One has the power plug and switch, plus the aforementioned main audio input. A slider switch for “Bass Boost” On/Off (I never noticed much of a difference either way) and speaker level output to drive the other speaker.

The volume knob is surrounded by a ring of plastic that glows blue when it is powered on. This light still illuminates, so I don’t think the problem is as simple as a blown fuse.

Looking inside the simpler box first, it’s hard to see very much through the small opening. The electronic bits we could see is probably an audio crossover circuit.

Moving on to the other speaker, we see a lot more and thankfully they’re more accessible as well. AC power enters the enclosure to an in-line fuse. (I didn’t think the fuse was the problem, but I checked anyway and there is indeed electrical continuity.) Power then flows to a transformer which steps ~120V AC down to ~14V AC. This stepped-down voltage connects to the circuit board, adjacent to a large four-pin package that looks like a rectifier.

Four sets of wires lead from this board into the speaker enclosure. The smallest and thinnest pair of wires go to the smaller speaker driver for higher frequencies, and the thicker pair goes to the larger driver. Two gray bundles lead to front-panel controls, one for the volume knob/power LED and the other for the auxiliary/headphone jacks.

Examining the circuit board, I see discoloration underneath these two components. Labeled Z1 and Z2 with diode symbols, I infer these are Zener diodes. Z2 was held down by a white-colored compound of unknown nature. That stuff was tenacious and refused to peel off, but I could cut it with a knife allowing me to unsolder both Z1 and Z2. Once removed I could read diode markings as IN4742A, confirming they are Zener diodes. I don’t have any replacements on hand, but I could give these two a quick basic test. With my multimeter switched to diode test mode, they read ~0.72V the one way and nothing the other. These are expected values of a diode proving they have neither failed open nor failed short. Circuit board discoloration showed that they’ve been running hot, but that fact by itself is not necessarily a problem with Zener diodes. A full diode test is beyond my abilities at the moment, so I soldered them back into the board and tested the speaker again. I had a slim hope that heat stress damaged a solder joint and resoldering them would bring the speaker back to life. No such luck, but it was easy to check.

Next, I looked into the still-functioning headphone jack. The speakers would go silent when audio is going through the headphones. Perhaps the jack is stuck in the “we have headphones” configuration. This would keep the speakers silent even when there are no headphones present. Unfortunately, the audio jacks are mounted on this circuit board, glued to the enclosure. Breaking the board free may be destructive, so I put this off to later.

Looking for promising components to investigate, I settled on the audio amplifier chip. It is a big component with large pins that I could probe, and its markings are visible for easy identification. I found and downloaded the datasheet for ST Electronics TDA7265 (25+25W Stereo Amplifier with Mute & Stand-By) and got to work understanding how it was used here.

I printed out a picture of the circuit board (*) so I could take notes as I probed the board (with the power off) while comparing it to TDA7265 datasheet information. The first order of business was looking for pins 1 and 6, which the datasheet said were both negative side of input power. I found those two pins connected to the same copper trace on the board leading to one pin of the rectifier, giving me confidence that I’m looking at the right part and I am oriented in the correct direction. I noted the pins I wanted to check once I’ve powered on the board:

  • Pins labeled R+ and R- should be DC power rectified from the ~14V AC transformer output. If there’s no voltage, I may have a dead rectifier.
  • There are two inputs, each with their positive and negative pins. I’m not sure which is wired as left and which is right, but I can connect a stereo signal to both input jacks. I should see line level voltage if audio signal makes it to the amplifier chip. If not, I can backtrack from here.
  • If audio makes it to input, I will probe Outputs 1 and 2, which should have speaker level voltage relative to a shared ground.
  • If there is input signal but no output, I will probe pin 5 which controls mute & standby behavior. See what voltages I read, and compare behavior to what datasheet says.

With this plan in hand, I prepared my tools. My LRWave web app written earlier for Lissajous experiments will provide test input signal. For probing the circuit, I have my multimeter and I have my oscilloscope. As a quick test, with the power still off I probed the audio input jacks while LRWave was running full blast. I measured ~0.6V AC on those pins (in the above photo, labeled in the lower right as “R IN, R GND, L IN, and L GND”.) This is a great start. I then turned on the power strip (powering up the speaker) and was immediately blasted by the sound of LRWave’s 440Hz sine wave.

The speaker works now! That is great, but… why does it work now? The last hardware modification I deliberately made to the device was to resolder Zener diodes Z1 and Z2. I tested the speakers then, and it didn’t make any sound. I must have made another (non-deliberate) change to the hardware to bring it back to life. Was it reaching for the audio jacks and jiggling a loose cable connection? Was it something I did by accident while probing the amplifier chip circuit? I don’t know. The speaker works again, but this success was unsatisfying. I wouldn’t call it “repaired”, either, as I can’t explain how I fixed it. It could just as easily and mysteriously break again tomorrow. But if it does, at least I have a plan to investigate for Round 2.


(*) The lone surface mount IC visible on this side is a ST TL074 quad op-amp.

Hamilton Beach Coffee Grinder (Type CM04 Model 80344)

The coffee drinker of the house has upgraded to a burr-type grinder for coffee beans, retiring this well-used unit which is now on the teardown bench.

It’s more accurately a coffee bean chopper, since it spins a set of blades to break them apart.

Cracks have started developing on its blade hub, which might be related to why one of the two blade tips drag on the bowl carving a channel. (Slightly out of focus in above picture.)

Mechanically, I’m curious to see implementation details for the cord management system built into the base. I expect the rest of the machine to be a shell around an AC motor spinning the blade.

I peeled off three rubber feet expecting to find fasteners hidden underneath, but there was nothing.

The base was actually held in place by a plastic retaining mechanism in the center. After popping off its smooth cosmetic cover, we could grasp the retainer to unlock it with a twist. Then the retainer could be removed, which released the base.

Power cord reel is visible after base was removed.

This little piece of plastic towards the end stops power cord from unwinding further, bumping up against a retaining ring. This retaining ring is held in place by four hooks. Gripping the ring with pliers and twisting clockwise a few degrees to slide past the hooks allowing removal of ring and power cord reel.

I was surprised to find a slip-ring style arrangement of metal rings and fingers. I had expected to see a very clever arrangement of bent and creatively routed wires to support power cord reel rotation without the parts count and complexity of a slip ring. I was wrong: it’s a slip ring.

Underneath the slip ring we see the first (and it turns out, the only) signs of traditional fasteners. Three Philips-head fasteners around the outside keep the motor frame in place.

What looks like a flat-head fastener in the middle is actually the motor shaft.

Putting a flat-head screwdriver on the motor shaft allows us to control its rotation and remove the blade. After blade removal, the motor could be maneuvered out the bottom.

With the motor out of the way, we could pry on plastic clips holding top ring in place. This one shows several scars from my efforts to release it.

With the ring removed, the control circuit slides out the top.

I had not noticed the safety interlock switch until I saw wires leading up to it. This ensures the lid must be in place before the blades would spin. It’s pretty clogged with coffee grounds which will eventually cause it to become unreliable.

The heart of the machine is a motor with the following printed on it:

HONDARAYA
Model:
UD1N00075DF
120V 60Hz

A web search found Hondaraya Engineering is a Hong Kong company, small enough of an operation that web search engines helpfully suggested I probably meant Honda the Japanese manufacturing giant. I wonder if Hondaraya was responsible for just the motor or if they were contracted by Hamilton Beach to engineer the entire grinder.

I was impressed by how this machine was designed. At its core, a pretty simple machine: a motor spinning a blade. The design and engineering team nevertheless devised a compact cord management system at the bottom. And it was held together almost entirely by cleverly designed plastic retaining mechanisms, the only exception were the three screws holding the motor frame in place. The lack of glue should mean easy assembly and repair, though replacement parts are not sold for this device. I never did find a good explanation why one blade tip has been dragging on the bowl. If a replacement blade were available, it would have been easy to replace and test to see if that would address the problem.

Capacitor Replacement on Insignia 100W Powered Subwoofer (NS-RSW211)

My home theater had a small powered subwoofer, an Insignia NS-RSW211 Rocketboost 6-1/2″ 70W Wired/Wireless-Ready Subwoofer. After several years of use, it started exhibiting some strange effects and I disconnected it. Since I’m not a huge home theater buff and it was a modest unit to begin with, I didn’t really miss its absence. It sat forgotten in a corner until I saw Monoprice held a sale on their item #8248, a similar-sized powered subwoofer that would be a great replacement. Before I hit “Buy” on the Monoprice item, though, I thought I should make an effort to fix the one I have.

The failing symptoms indicate an intermittent connection somewhere in the system. When I turn on the subwoofer, it is fine for the first few minutes. After that initial period, sound would start cutting in and out at irregular periods. Every time it cuts out, the low bass sounds disappear. When it cuts back in, a deep “thump” announces return of low frequencies. This would start out tolerably infrequent, like hearing a distant firework show. Interruptions then become increasingly frequent. Eventually it will sound like automatic weapons fire in the background even when we’re not watching an action film, at which point I would turn it off. After a few hours of rest, I could repeat the cycle. Intermittent issues are always annoying to diagnose (part of why I’ve been putting it off) but I should at least take a look. On to the workbench it goes!

There are a lot of fasteners visible on this back plate. This is not a huge surprise: a subwoofer’s job is to push those low frequency thumps. Each thump will rattle anything not securely fastened, and every thump will be trying to loosen every fastener. In fact, the large numbers of fasteners are quite welcome: if it had been glued together, opening it up would be a destructive act making a successful repair unlikely.

But it wasn’t glued, so I could get to work. Removing the outermost eight fasteners allowed me to remove the rear module. I was a little surprised to see all electronics were sealed inside an airtight box. This might be good for acoustics but bad for air cooling circulation. The only thing poking into the acoustic chamber are the pair of speaker wires going to the driver itself. They used commodity spade connectors and were easy to disconnect so I could focus on the electronics box.

Removing the next outermost set of six fasteners allowed me to open up the electronics box. I was greeted with the thick stench of fried electronics. Something definitely died in here and, if it smelled this strong, I should be able to see it.

Yep, there it is. Capacitor C28 is toast. Finding this dead capacitor is good news, much easier than diagnosing an intermittent issue. The bad news is I’m not familiar enough with power supply theory of operation to explain why this absolutely and completely dead capacitor would cause an intermittent failure.

One end has completely blackened and appears to have broken open as well.

The yellow circuit board appears to be the power supply subsystem. 120V AC power cable (black & white wires) goes to the power switch, then into one corner of this yellow board near the dead capacitor. Diagonally opposite them is this connector delivering +24V to the rest of the subwoofer.

Unplugging AC input and DC output wires, then removing four screws, allowed removal of this power supply board so I could unsolder the dead capacitor easily. It came off in two separate pieces, very dead.

Reading markings on the charred capacitor carcass was a challenge. After playing with lighting, camera settings, and photo editing, I could make it out as:

105K
250KC

I’m not familiar with this type of capacitor and didn’t know how to interpret those numbers. Looking around online, I found this page which said “105” meant 10 * 105 pF = 1000000 pF = 1000 nF = 1 uF and the “K” meant +/- 10% tolerance. The voltage rating portion didn’t line up with anything on that page, though. I’m inferring that “250KC” means something that can handle up to at least 250V, as this device can take up to 230V AC input.

Looking around my various assortment trays of capacitors, I didn’t find anything +/- 10% of 1uF. I then looked through my pile of teardown remnants for capacitors to salvage. The closest candidate was a 0.68uF 450V capacitor from the Antec power supply that caught on fire.

It even had the same footprint as the original toasted capacitor, making for an easy fit in the available space. However, 0.68uF is still short of the capacitance of the original so I continued looking.

I found a 0.22uF 250V capacitor inside the surprisingly complex evaporator fan. There was a clear conformal coating over everything that made removal a bit of a pain (and the result looking messy.) But they gave me a theoretical 0.68uF + 0.22uF = 0.90uF and my multimeter says they’re actually a tiny bit above rated value. Bringing me within 10% of 1uF, good enough for a test run.

Since the original capacitor slot was already occupied by the 0.68uF capacitor, the second parallel capacitor had to sit on the back.

I buttoned everything back up and preliminary test looks promising. After playing through a two-hour movie, I have yet to hear the thumping “fireworks” to “gunfire” failure sequence. Still unknown: what killed the original capacitor, and whether the same will happen to these replacements. Time will tell. In the meantime, I’ve managed to keep something out of landfill and resisted the temptation to buy a Monoprice powered subwoofer on sale. I’m thankful the design & engineering team built this device in a repairable way.

High Power 600W Power Supply (HP1-J600GD-F12S)

Along with the “keyboard is broken” laptop, I was also asked to look into a mid-tower PC that would no longer turn on. I grabbed a power supply I had on hand and plugged it into the motherboard, which happily powered up. Diagnosis: dead power supply. I bought a new power supply for the PC to bring it back to life, now it’s time to take apart the dead power supply to see if I can find anything interesting. Could it be as easy as a popped circuit breaker or a blown fuse?

According to the label, the manufacturer has the impossibly unsearchable name of “High Power”. Fortunately, the model number HP1-J600GD-F12S is specific enough to find a product page on the manufacturer’s site. The exact model string also returned a hit for a power supply under Newegg’s house brand Rosewill, implying the same device was sold under Newegg’s own name. Amusingly, Newegg’s Rosewill product listing included pictures with “High Power” embossed on the side.

If there is a user-replaceable fuse or a user-accessible circuit breaker, they should be adjacent to the power socket and switch. I saw nothing promising at the expected location or anywhere else along the exterior.

Which meant it was time to void the warranty.

Exterior enclosure consisted of two pieces of sheet metal each bent into a U shape and held together with four fasteners. Once pried apart, I had to cut a few more zip-ties holding the cooling fan power wire in place before I could unplug it to get a clear view at the interior. Everything looks clean. In fact, it looked too clean — either this computer hadn’t been used very much before it blew, or it lived in a location with good air filtration to remove dust.

Still on the hunt for a circuit breaker or a fuse, I found the standard boilerplate fuse replacement warning. Usually, this kind of language would be printed immediately adjacent to a user-serviceable fuse. But getting here required breaking the warranty seal and none of the adjacent components looked like a fuse to me.

Disassembly continued until I could see the circuit traces at the bottom of the board. Getting here required some destructive cutting of wires, so there’s no bringing this thing back online. Perhaps someone with better skills could get here nondestructively but I lacked the skill or the motivation to figure things out nicely. I saw no obviously damaged components or traces on this side, either. But more importantly, now I could see that 120V AC line voltage input wire is connected to a single wire. That must lead to the fuse.

Turning the board back over, I see the line voltage input wire (brown) connected to a black wire that led to a cylinder covered in heat-shrink tubing and held in place by black epoxy. The shape of that cylinder is consistent with a fuse. The heat-shrink and epoxy meant this is really not intended to be easily replaced.

Once unsoldered, I could see the electronic schematic symbol for fuse printed on the circuit board. The “F” in its designation “F1” is consistent with “Fuse”, as do the amperage/voltage ratings listed below. This fuse is a few centimeters away from the caution message I noticed earlier, which was farther away than I had expected. My multi-meter showed no continuity across this device, so indeed the fuse has blown. I cut off the heat-shrink hoping to see a burnt filament inside a glass tube, but this fuse didn’t use a glass tube.

I started this teardown wondering if it was “as easy as a popped circuit breaker or a blown fuse”. While it was indeed a blown fuse, a nondestructive replacement would not have been easy. I don’t know why the fuse on this device was designed to be so difficult to access and replace, but I appreciate it is far better to blow a fuse than for a failing power supply to start a fire.

Zalman 120mm Case Fan, Clear with Blue LED (ZA1225CSL)

After years of faithful service, this particular cooling fan has worn down to a point where it would vibrate noisily, its associated friction dragging down fan blade speed. Time for me to retire it but not before subjecting it to a teardown.

Sticker on the back says it is a Zalman model ZA1225CSL.

This particular fan was cast in clear plastic and has embedded blue LEDs for visual novelty.

Four LEDs are angled such that they turn fan blades into LED light pipes creating an illuminated arc while the fan spun.

A glued-on clear cover hides the LED within. Getting good leverage on this cover is tough with the fan blades in place, so I’ll work on removing the fan first.

A razor blade made quick work of the rear sticker.

Under the sticker, we can see fan motor shaft held in place by a small white plastic ring.

Remove the ring (not terribly visible against a white background, I admit) and the fan hub slides free. Despite the racket it has been making, I see no obvious signs of wear on either this fan hub shaft or the hub bearing. I guess a tiny amount of wear was enough for the system to start wobbling.

It was easy to break those LED covers free once fan blades were no longer in the way.

The blue LEDs appear to be standard 3mm diameter units, powered by wires that were glued into channels molded into fan hub support beams. Pulling them free destroyed the clear insulation on those wires. Given how affordable LEDs are now, there’s not much point trying to salvage these LEDs beyond trying to see if I could. I had a 75% success rate: one LED out of four was torn off its wires, oops.

I removed the fan hub, and it appears this chip is in charge of the operation. Marked FTC S276.2QD, a web search found this to be the FS276 two-phase DC motor control chip by FTC. The website indicates Feeling Technology Corp is a Taiwan-based semiconductor company. The chip’s datasheet shows an integrated hall effect sensor, which explains why it is positioned to pick up magnetic field of the fan rotor. It has four pins: power on one end, ground on the other, and sinks for two motor phases.

The single-sided circuit board marked ZB111228 implemented the FS276 datasheet circuit with a few additions. Around the perimeter, we have pads for the four blue LEDs, each connected to power and ground through a current-limiting resistor marked with 681. I believe this means 68 * 101 = 680 ohms. We also have a transistor, connected to one of the two motor phases, to communicate tachometer signal.

I will likely find a use for the three-conductor wire with PC cooling fan connector on one end. I might stick the blue LEDs on a future project just for laughs. The motor control circuit board will go to electronic recycle. All the clear plastic will go to landfill.

MageGee Wireless Keyboard (TS92)

In the interest of improving ergonomics, I’ve been experimenting with different keyboard placements. I have some ideas about attaching keyboard to my chair instead of my desk, and a wireless keyboard would eliminate concerns about routing wires. Especially wires that could get pinched or rolled over when I move my chair. Since this is just a starting point for experimentation, I wanted something I could feel free to modify as ideas may strike. I looked for the cheapest and smallest wireless keyboard and found the MageGee TS92 Wireless Keyboard (Pink). (*)

This is a “60% keyboard” which is a phrase I’ve seen used two different ways. The first refers to physical size of individual keys, if they were smaller than those on a standard keyboard. The second way refers to the overall keyboard with fewer keys than the standard keyboard, but individual keys are still the same size as those on a standard keyboard. This is the latter: elimination of numeric keypad, arrow keys, etc. means this keyboard only has 61 keys, roughly 60% of standard keyboards which typically have 101 keys. But each key is still the normal size.

The lettering on these keys are… sufficient. Edges are blurry and not very crisp, and consistency varies. But the labels are readable so it’s fine. The length of travel on these keys are pretty good, much longer than a typical laptop keyboard, but the tactile feedback is poor. Consistent with cheap membrane keyboards, which of course this is.

Back side of the keyboard shows a nice touch: a slot to store the wireless USB dongle so it doesn’t get lost. There is also an on/off switch and, next to it, a USB Type-C port (not visible in picture, facing away from camera) for charging the onboard battery.

Looks pretty simple and straightforward, let’s open it up to see what’s inside.

I peeled off everything held with adhesives expecting some fasteners to be hidden underneath. I was surprised to find nothing. Is this thing glued together? Or held with clips?

I found my answer when I discovered that this thing had RGB LEDs. I did not intend to buy a light-up keyboard, but I have one now. The illumination showed screws hiding under keys.

There are six Philips-head self-tapping plastic screws hidden under keys distributed around the keyboard.

Once they were removed, keys assembly easily lifted away to expose the membrane underneath.

Underneath the membrane is the light-up subassembly. Looks like a row of LEDs across the top that shines onto a clear plastic sheet acting to diffuse and direct their light.

I count five LEDs, and the bumps molded into clear plastic sheet worked well to direct light where the keys are.

I had expected to see a single data wire consistent with NeoPixel a.k.a. WS2812 style of individually addressable RGB LEDs. But label of SCL and SDA implies this LED strip is controlled via I2C. If it were a larger array I would be interested in digging deeper with a logic analyzer, but a strip of just five LEDs isn’t interesting enough to me so I moved on.

Underneath the LED we see the battery, connected to a power control board (which has both the on/off switch and the Type-C charging port) feeding power to the mainboard.

Single cell lithium-polymer battery with claimed 2000mAh capacity.

The power control board is fascinating, because somebody managed to lay everything out on a single layer. Of course, they’re helped by the fact that this particular Type-C connector doesn’t break out all of the pins. Probably just a simple voltage divider requesting 5V, or maybe not even that! I hope that little chip at U1 labeled B5TE (or 85TE) is a real lithium-ion battery manage system (BMS) because I don’t see any other candidates and I don’t want a fiery battery.

The main board has fewer components but more traces, most of which led to the keyboard membrane. There appears to be two chips under blobs of epoxy, and a PCB antenna similar to others I’ve seen designed to work on 2.4GHz.

With easy disassembly and modular construction, I think it’ll be easy to modify this keyboard if ideas should strike. Or if I decide I don’t need a keyboard after all, that power subsystem would be easy (and useful!) for other projects.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Microwave Turntable Repair

My microwave is getting older and sometimes doesn’t heat food as much as expected. I kept using it after an earlier test of its heating power was inconclusive. A few days ago, a new problem cropped up: after an audible mechanical noise, the turntable stopped turning. This led to uneven heating, and I thought maybe it’s time to get a new microwave. Before I spent money, though, I wanted to take a look at the turntable motor and see if I can apply any lessons learned from my earlier teardown of a similar motor.

This microwave was a Sharp R-309YK and I was pleasantly surprised there was design effort for ease of repair. An access panel is stamped into the bottom of the microwave held by four small tabs of metal.

Using a pair of pliers, I twisted off those four small tabs and removed the panel. We see the turntable motor identified as 49TYZ-A1 by Yuyao Yahua Mechanical & Electrical Co., Ltd. I don’t know how important it is to buy the exact replacement, there are a lot of similar motors in this form factor. The only significant variation I noticed was the shape and length of the output shaft.

Before I buy a new motor, I had nothing to lose by taking a closer look at this one. I applied 110V power and nothing moved. The problem is indeed here rather than somewhere else in the microwave.

Following precedent of my previous teardown, I opened up the faceplate to look for a mechanical obstruction or anything else that would explain why the motor wouldn’t turn. I thought maybe a gear snapped a tooth, but there was nothing of the sort. I removed one gear after another until I was left with only the rotor, which did not live up to its name because it did not rotate under power.

I picked up the rotor for a closer look, and I noticed a crack running across its magnet. Tiny pieces of magnet had chipped off the edge of the crack. After clearing out the tiny chips and dropping the rotor back in, it spun up under power. I guess a lodged chip of magnet was enough to keep the rotor from starting up? But the rotor made a lot of intermittent noise while spinning. The click clack noise sounded like a tiny part catching on a physical obstruction and tapping it. But I had no luck finding the culprit. If it’s another magnet chip, I couldn’t find it. Hypothesis: centripetal force acting on the cracked magnet opened it up to a C shape and pulling a corner far enough out it is barely tapping some other part of the motor. If true, that’s not good because it will quickly produce more magnet chips and stop the motor again.

Fortunately, I had kept the rotor from my previous turntable motor teardown. I had disposed of most of the motor but kept the rotor because I wanted to visualize its magnetic field. Using my calipers, I confirmed that all major dimensions were nearly identical.

It seems to be a drop-in replacement, spinning up without the click clack noise. I reassembled the motor and reinstalled it in the microwave. A quick test confirmed that my turntable is turning again with this salvaged rotor.

All I had to do was reinstall the access panel, which was designed so that I could turn it 180 degrees and insert tabs to fit into precut slots. It just needed an appropriately sized screw that could self-tap into sheet metal. I found one in my stockpile of fasteners, and we are good to go. I didn’t need to buy a new microwave today, I didn’t even need to buy a new turntable motor. I appreciate Sharp engineers for stamping in an access panel to make this project so much easier than it would have been otherwise.

FormLabs Form 1+ Z-Axis Assembly

I think I can find new useful homes for several components of a broken FormLabs Form 1+ laser resin 3D printer. After carefully removing its laser optical core, I proceed to attempt salvaging its Z-axis actuator.

The Z-axis motion in this printer is driven by a stepper motor turning an Acme thread leadscrew. This concept is pretty commonly found in FDM 3D printers as well, but closer inspection unveiled a higher quality design. The first hint was the limit switch at the top. Cheap FDM printers use a microswitch, this printer uses an optical interrupter. Eliminating the flexible spring in a microswitch makes this limit switch more precise in marking its location. The print platform is mounted on a ball bearing carriage traveling on a guide rail, again more precise than the typical FDM printer usage of sleeves traveling on rods.

And finally, I noticed a detail significant in its absence: there is no shaft coupler between motor and leadscrew. A leadscrew as motor output shaft eliminates all problems introduced by couplers. No set screws to back out, no errors in concentricity between the two shafts, etc. Markings on the motor says LDO-42STH34-L291E. We can find LDO Motor’s page for their LDO-42STH line of 42mm hybrid stepper motors, but this particular model number is not listed. Searching for similar items revealed several other LDO motors with a leadscrew output shaft, all at significantly higher cost than generic NEMA17 stepper motors + leadscrew + coupler. Looks like this particular FormLabs motor variant is an engineering tradeoff of higher parts cost for higher precision.

However, all this precision means I have to make a decision on salvaging these parts. The linear rail, optical interrupter limit switch, and stepper motor are all mounted to the printer chassis. The chassis is constructed from several sheets of stamped sheet metal, folded and riveted together for rigidity. Good for optical stability, bad for me. If I remove each component separately, their relative precision alignment would be lost. If I want to remove the Z-axis as an intact sub assembly from the printer chassis, I have to perform the irreversible act of drilling out some rivets. After some thought I decided on the latter option.

Drilling out rivet heads would generate a lot of metal shavings. So before I got started with that destructive act, I wanted to remove the main mirror and get it away from scratch-inducing shavings.

The back side of the mirror has been glued to a metal plate with two embedded threaded rods. Removing two nuts freed the mirror assembly.

With the mirror stored safely away, it’s time to make some chips.

Roughly half an hour later, I’ve freed the Z-axis subassembly from all other pieces of stamped and riveted sheet metal.

I thought about grabbing my angle grinder to cut off the bottom, as it is not strictly related to the Z-axis assembly. But this is where the laser optical subassembly was mounted, and it’s also where the mirror was mounted. There’s a chance these pieces of sheet metal may yet be useful. Besides, it’s only minimally more than keeping the Z-axis itself. Even with this bottom portion, this subassembly is a lot less bulky than keeping the rest of the printer chassis together. And small enough for me to lay out everything on my workbench.

NEXTEC Work Light LED Array

While experimenting with 5V power delivery over USB-C, I thought of an experiment that will utilize my new understanding of computer cooling fan tachometer wire. For this experiment I will need a light source in addition to the fan itself. I wanted a nice and bright array of many LEDs, and preferably something already set up to run at around 12V so I wouldn’t have to add current-limiting resistors. A few years ago, I took apart a Sears Craftsman NEXTEC work light for its battery compartment. Now it is the LEDs turn to shine. That battery pack used three lithium 18650 cells in series, so it is in the right voltage range.

I think there was only a single fastener involved in this LED array, and it was already gone from teardown earlier so now everything slid apart easily.

I like the LED housing and intend to use it, but I wanted to take a closer look at the LED array.

I confirm the 24 white LEDs visible before disassembly, and there’s nothing else hiding on this side of the board, just the power supply wires looping through for a bit of strain relief. We can also see that Chervon Group was the subcontractor who produced this device to be sold by Sears under their Craftsman branding.

Everything is on the backside of this circuit board. From here we can see the 24 LEDs are arranged in 12 parallel sets of 2 LEDs in series, each set with a 240 Ohm resistor between them. Beyond that, to lower left I see a cluster of components and I’m not sure what they do. My best guess is battery over-discharge protection. Perhaps the component marked ZD1 is a Zener diode to detect voltage threshold, working with power transistor Q1 to cut power if battery voltage drops too low.

The most important thing is that I don’t see a microcontroller that requires time to boot up. I will be pulsing this LED array rapidly and want minimal delay between power and illumination. If delay proves to be a problem, I’ll try bypassing those lower-left bits: Relocate the power supply wire (brown wire, connects between markings R1 and ZD1) so it connects directly to the LED supply plane. Either to the transistor tab adjacent to the Q1 marking, or directly to the high end of any of those 12 parallel LED strings. But I might not need to perform that bypass. I will try my experiment with this circuit board as-is.

Asus Wireless Router (RT-N66R)

Taking apart a broken Ethernet switch reminded me that I have another piece of networking equipment that had been retired and sitting in a box. It was my Asus RT-N66R wireless router that I retired because its gigabit Ethernet ports started failing. After years of use I lost one port, and within two weeks I lost another port. I took those two consecutive port failures as a sign of impending total failure and quickly replaced it.

One thing that I remembered about this router was that it ran hot. Really, really hot. The power supply is rated at 19V DC @ 1.58A. That’s 30 watts of electricity pumped into a device without active cooling or even a metal case for passive heat dissipation. I wouldn’t be surprised if its failure can be traced to heat.

Four rubber feet on the bottom concealed four Philips-head fasteners. Once they were removed, though, the router was not inclined to come apart. Its top and bottom halves were held together by hooks inside these very robust loops. While undoing these assemblies, I noticed that plastic on one side of the router is much more brittle than the other side. Might this be a result of long-term heat exposure?

Removing the top exposed this aluminum heatsink up top, oddly situated far away from vents along the sides and bottom of the device. It explained why the top surface was so warm to the touch. Bare copper traces visible on the circuit board show signs of discoloration that may or may not be heat.

Towards one corner I saw two items of interest: a 4-pin header labeled with VCC, RX, TX, and GND that indicated an UART connection. And not far away, what looks like an empty microSD card slot. Asus routers run their fork of DD-WRT and it is possible to install custom builds of DD-WRT. I assume this UART and microSD would be handy for such enterprises. But we now live in the age of Raspberry Pi and BeagleBone so having a small network-capable Linux computer is not the novelty it once was. I’m not going to bother, especially as this hardware has started to fail.

Flipping the assembly over, I expected to see another finned heatsink for dissipating heat out of those ventilation slots on the bottom, but I only saw this sheet of metal. Likely aluminum.

And it’s not even a heatsink. There was no surface contact with any electronic components. It made contact only with six brass standoffs, none of which had any connection to the finned heatsink on the other side. If anything, the air trapped between it and the circuit board would have kept heat inside. I’m very mystified by the thermal engineering of this router.

Said heatsink were held on by four plastic retainers, two on each side. Here’s a closeup of one side. They have become very brittle and shattered when I tried to release them.

Once the heatsink was removed, we have our first sighting of thermal pads, but they sat on top of thin metal shields for radio-frequency (RF) isolation.

Prying off those shields revealed four more thermal pads, one on each of four important-looking chips.

The biggest thermal pad sits on the most important looking chip, a Broadcom BCM4706KPBG. A quick web search indicates this is a MIPS32 architecture CPU. Remaining three chips with thermal pads all have a Broadcom logo on top, but text information below that logo were very hard to read.

I saw no obvious damage that would explain why two out of four Ethernet ports failed, nor do I see anything I could conceivably salvage and reuse with my current skill level. Plastic enclosure will go to landfill, aluminum heat sink and sheet will head to metal recycle, and the circuit board will go to electronic waste disposal.

TP-Link 8-Port Ethernet Switch (TL-SG108)

Latest visitor to the teardown workbench is a TP-Link 8-port Gigabit Ethernet Switch. When plugged in to power, I see the power LED illuminate. But when I plug in an Ethernet cable, its corresponding activity LED stays dark. It’s not just an indicator light failure, no networking traffic flows through this switch at all. All the cables act as if they were not plugged in.

I don’t expect to see very much inside, but I still wanted to take a look. Also, disassembly will allow me to separate its metal enclosure (sent to normal recycle) from its internal circuit board (for electronic waste.)

Removing two externally accessible fasteners allow me to slide the top lid away, reveling the circuit board held by four more fasteners. Removing them released the circuit board. Nothing tricky here.

There is one obvious large chip in charge of the operation, but there is a heatsink epoxied to its surface so I could not read its label. There are eight large rectangular Group-Tek HST-2027DAR network transformers, one per port. Each of them embeds many little coils inside to carry network data while keeping things electrically isolated. (A picture showing internals of a similar Ethernet transformer is available in Open Circuits.)

With so few components, it didn’t take long for me to inspect them and verify there were no obvious signs of failure. There were several unpopulated footprints, but those looked deliberate. The lone exception is C88 which looks to have been torn off. There should have been a tiny capacitor complementing its twin C87. I don’t think a single capacitor would explain a complete failure of the switch, though.

Another feature visible in this closeup is a large sprinkling of dimples that I associate with circuit board vias – holes drilled through the substrate to connect to another circuit board layer. They’re usually done to conduct signal to another layer. (For an example see the near end of R38, visible in this picture towards the left.) But this board had so so many vias! Do they all go to the other side of the board?

Yes they do! I’ve seen generous vias done in the name of heat dissipation, but thermal management vias would be concentrated around heat-generating components. These vias are scattered throughout the board, surrounding the many traces carrying Ethernet data. Which leads to my new hypothesis: these are all part of the ground plane, helping maintain integrity of signal traveling over data wires.

Logitech Wireless Trackball (M570)

I have always preferred trackballs over mice for my desktop pointing device. A preference very much related to the fact that I’ve always had a cluttered desk and a trackball requires less desk space than a mouse. Trackballs also come in varying layouts. I prefer those that put the trackball under my fingers, and I click buttons with my thumb. (Like this design I’m currently using. *) Others put the trackball under the thumb instead and leave buttons to be pressed like a mouse.

This Logitech M570 trackball used the latter layout. I tried it for a few weeks and decided I didn’t like it, so it’s been gathering dust ever since. Now I’ll take it apart to look inside, evaluating it for a project idea.

There was one visible fastener on the bottom, which is curious because it was adjacent to a rubber foot. There are three other rubber feet on this trackpad, each of which hid a fastener. Why was the fourth foot unable to hide a fastener?

After removing those four fasteners, I had expected the trackball to come apart easily. It did not, acting as if there were at least one more screw holding things together. Applying lesson learned from my Microsoft Arc Mouse teardown, I peeled back the battery tray sticker. Aha! Gotcha, you little sneak.

Once that final fastener was removed, the top and bottom halves came apart easily. There was only a very small circuit board inside. Two if you count the tiny raiser board hosting SW4 and SW5. The trackball position sensor is at an angle relative to the main circuit board, and engineers solved that challenge with a short length of flex cable.

The most significant chip on the top of the circuit board is an ATmega168PA, a close relative of the ATmega328P made popular by Arduino.

The two main buttons were large pieces of plastic that could be unclipped. Their motion actuates two long black Omron tactile switches. Between them lies an optical emitter and receiver to read scroll wheel motion.

Looking at the scroll wheel we can see slits for the optical encoder. A short length of spring pushes against the interior surface of this wheel, which has a wavy texture. Combination of spring and texture results in scroll “step” tactile feedback.

A few components are visible on the bottom of the circuit board including the power switch.

The most significant looking chip on the bottom is a nRF24L01+, a popular 2.4GHz wireless transceiver chip that we can get in cheap breakout boards (*) for hobbyist wireless projects.

Between the ATmega168PA up top and the nRF24L01+ on the bottom, it is tempting to see if I can reprogram this trackball for complete firmware control. We even see an array of eight potential test and diagnostics pads on the bottom of this board. That might be a fun project, but I had something much more straightforward in mind.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Monoprice Monitor Internals: Round 2 (10734)

Leveraging Bitluni’s work, I was able to convert one of my ESP32 into a VGA signal generator that outputs full-screen white. This gave me a low-impact way to convert a malfunctioning monitor into a lighting fixture. But the low-impact way is definitely not the optimal way, because it meant I would need a VGA cable dangling outside of the screen, connected to an ESP32, which needs its own power supply. What are my other options? The first time I opened up this monitor, I didn’t understand very much of what I had looked at. A few years of tinkering lessons have been added to my brain, so I’ll open it up again for another look.

This display was spared from the Great Backlight Liberation because it could still be powered on, but once I had it open, I wanted to examine its backlight in light (ha ha) of new knowledge. I found the likely wire harness for this panel’s backlight, a respectable bundle of twelve wires. Flipping over the circuit board, I see those wires were labeled with:

  • G_LED1-
  • G_LED2-
  • G_LED+
  • B_LED+
  • B_LED1-
  • B_LED2-
  • B_LED3-
  • B_LED4-
  • B_LED+
  • G_LED1
  • G_LED3-
  • G_LED4-

Based on these labels, we can infer there are four “G” LED strings and four “B” LED strings, each with their own “-” wire. There are two wires for “B_LED+”, but the “G” LEDs have separate “G_LED+” and “G_LED1”. I don’t know why they were labelled differently, but my multimeter found electrical continuity between “G_LED+” and “G_LED1” so they are wired in parallel, as are those two “B_LED+” wires. Leading me to believe that “G” and “B” LEDs each have two “+” wires corresponding to four “-” wires. So far, so good. I then turned on the monitor to probe voltage levels of these wires. I had expected something in the neighborhood of the 24V DC power supply that feeds this monitor, but my meter said the voltage level is actually in the neighborhood of 64V to 68V DC. Yikes! That’s well above maximum voltage of any boost converter I have on hand, so driving the backlight without this board wouldn’t be my top choice.

I see inductors and capacitors that are likely the boost conversion circuit for this backlight, but I didn’t see a promising chip that might be a standalone LED driver like I see in some laptop panel teardowns. I think it is all controlled by that central main chip sitting under a heatsink. I couldn’t make it drive the backlight with a PWM signal like I could the laptop panel, so I have to stay with the ESP32 VGA signal generator.

The next question is then: could I use this board to drive just the backlight? To test this possibility, I unplugged these two cables connecting to the LCD array. Some of these wires carry power, the rest carry LVDS pixel data. When fed with VGA data from my ESP32, this control board happily powered up the backlight even when it couldn’t communicate with the LCD array. This is a very promising find, but I’m not ready to commit to a destructive separation just yet.

By itself, without an incoming video signal, this monitor quickly goes to sleep mode. I know that my ESP32 VGA signal can keep it awake past that initial sleep mode, but I’m not yet confident everything else will continue running for the long term. The only diagnostic channel I have for this system is the on-screen display, and if I should separate the LCD from its backlight, I would no longer be able to read the on-screen display.

It’s very tempting to separate them now, because I know a lot of light is trapped back there. Look at the brightness difference when I compared a bare backlight with the same non-broken (and non-separated) Chromebook panel. I expect there to be a very bright backlight behind this LCD. But for the sake of doing things incrementally, I’ll leave the LG display module intact for now and focus on integrating my ESP32 VGA signal generator.

Notes on “Open Circuits” by Eric Schlaepfer and Windell H. Oskay

I am interested in electronics, in teardowns, and in electronics teardowns. Thus I was the exact audience for a book coming out soon: Open Circuits by Eric Schlaepfer and Windell H. Oskay. I preordered directly from publisher No Starch Press, which also granted me access to an early access eBook. I’ve finished browsing through that PDF and loved every page of it. I look forward to having the print book in my hand.

I first became aware of these cutaways from Twitter, where author Eric Schlaepfer tweeted a few cross sections shot with a cell phone camera via @TubeTimeUS. Feedback was positive, encouraging Eric to repeat the same treatment for more components, improving the techniques as he went. Things got popular enough that a vocal subset of his new Twitter following got grumpy when he went back to his regular programming. (Paraphrasing his reply: “Come on, guys, this account isn’t @CrossSectionTimeUS.”) Still, people loved the cross-sections and some said “I would love to have these pictures in a coffee-table book.” Thus this book Open Circuits.

Every component cross-sectioned in the book is accompanied by a brief explanation of the component. Knowing what a component does and how its internals accomplish the objective helps give us context to understand what we see in the pictures. Sometimes there’s a diagram with subcomponents called out as a visual explanation augmenting the text description. I knew roughly what some of these components did, but most of them were new information for me. But even if I had known of a component, usually I hadn’t known what it looked like inside! Every page is a new discovery. Occasionally, I even recognized something that I’ve seen before. For example, I recognized a thermal switch as something I took out of a retired coffee maker but I wasn’t sure what it was until I saw one explained and cross-sectioned.

This book is aimed at people who want to know more about what happens behind the scenes, so naturally the book covered that as well: the afterword section describes the techniques that went into this book’s photography. From cutting and polishing of components, to cleaning and mounting, to the photography process. Starting with cameras and lenses, to macro photography, and finally focus stacking to compose the sharp pictures in the book.

If you’ve read this far, you will enjoy the book as well.


I earn nothing from endorsing this book, I just love it.

Radeon HD 7950 Video Card (MSI R7950-3GD5/OC BE)

This video card built around a Radeon HD 7950 chip is roughly ten years old. It is so outdated, nobody would pay much for a used unit on eBay. Not even at the height of The Great GPU Shortage. I’ve been keeping it around as a representative for full sized, dual-slot PCIe video cards as I played with custom-built PC enclosures. But I now have other video cards that I can use for the purpose, so this nearly-teenager video card landed on the teardown bench.

Most of its exterior surface is covered by a plastic shroud, but the single fan intake is no longer representative of modern GPUs with two or three fans.

Towards the center of this board is a metal bracket for fastening a heat sink that accounted for most of the weight of this card. In the upper left corner are auxiliary PCIe power supply sockets. The circuit board has provision for a 6-pin connector adjacent to an 8-pin connector, even though only two 6-pin connectors are soldered to this board. Between those connectors and the GPU itself, I see six (possibly seven) sets of components. I infer these are power-handling parts working in parallel to feed a power-hungry chip.

This was my first 4K UHD capable video card, which I used via the mini-DisplayPort connectors on the right. As I recall, the HDMI port only supported up to 1080p Full HD and could not drive a 4K display. Finally, a DVI port supported all DVI capabilities (not all of them do): analog VGA on its DVI-A pins, plus dual-link DVI-D for driving larger displays. I don’t recall if the DVI-D plug could output 4K UHD, but I knew it went beyond 1080p Full HD by driving a 2560×1600 monitor.

The plastic shroud was held by six plastic screws to PCB and two machine screws to metal plate. Once those eight fasteners were removed, shroud came off easily. From here we get a better look at the PCIe auxiliary power connectors on the top right, and the seven sets of capacitors/inductors/etc. that work in parallel to handle power requirements of this chip.

Four small machine screws held the fan shroud to the heat sink. Fan label indicates this fan consumes up to 6 Watts (12V 0.5A) and I recall it can get move a lot of air at full blast. (Or at least, gets very loud trying.) It appears to be a four-wire fan which I only recently understood how to control if I wanted. Visible on the fan’s underside is a layer of fine dust that held on, despite a blast of compressed air I used to clean out dust bunnies before this teardown.

Some more dust had also clung on to these heat sink fins. It seems like a straightforward heat sink with stamped sheet metal fins on an aluminum base, no heat pipes like what we see on many modern GPUs. But if it is all aluminum, and there are no heat pipes, it should be lighter weight than it is.

Unfastening four machine screws from the X-shaped rear bracket allowed me to remove the heat sink, and now we can see the heat sink has a copper core for heat distribution. That explains the weight.

The GPU package is a high-density circuit board in its own right, hosting not just the GPU die itself but also a large collection of supporting components. Based on the repeated theme of power handling, I guess these little tan rectangles are surface mount capacitor arrays, but they might be something else.

Here’s a different angle taken after I cleaned up majority of thermal paste. An HD 7950 is a big silicon die sitting on a big package.

When I cleaned all thermal paste off the heatsink, I was surprised at its contact surface. It seems to be the direct casting mold surface texture with no post-processing. For CPU heatsinks, I usually see a precision machined flat surface, either milling or grinding. Low-power/low-cost devices may skip such treatment for their heatsinks, but I don’t consider this GPU as either low power or low cost. I know this GPU dissipated heat on par with a CPU, yet there was no effort for a precision flat surface to maximize heat transfer.

I think this is a promising module for reuse. Though in addition to the lack of precision flat surface, there’s another problem that the copper core is slightly recessed. The easiest scenario for reuse is to find something that sticks up ~2mm above its surrounding components, but not by more than the 45x45mm footprint of this GPU. This physical shape complicates my top two ideas for reuse: (1) absolute overkill cooling for a Raspberry Pi, or (2) retrofit active cooling to the passively-cooled HP Split X2. If I were to undertake either project, I’d have to add shims or figure out how to remove some of the surrounding aluminum.

Solar Powered Dancing Duck

A small solar cell doesn’t get much power with indoor lighting. As far as consumer electronics go, I haven’t seen much beyond a solar-powered desktop calculator. I had thought there’d never be enough power for an indoor solar mechanical device, but a few years back little solar-powered pendulum toys started showing up. I usually see them as little waving cats (maneki-neko) like the teardown and analysis posted to Hackaday.

This device is a variation of the same basic idea. Instead of waving a cat’s arm, the pendulum swings the body. An additional sophistication in this design is a second linkage that swings the head in the opposite direction of the body, creating a dancing duck. It was purchased for a buck and a half from Daiso Japan, so we’re looking at something produced for raw material cost somewhere a quarter (if even that much.) It was an impulse buy and wasn’t expected to last very long, but it actually ran for years before suffering mechanical issues and frequently getting stuck. It was then moved to a window ledge, where it could occasionally swing its head and hips under power of direct sunlight. But the sun that gave it a second life also took away its shine: brightly colored plastic started fading rapidly and became brittle. Finally, an unfortunate fall from that window ledge ended this duck’s performance career.

Poor duck broke its neck in the fall. The neck linkage was lost, but we can see the head’s pivot point inside the neck, where plastic shaded from direct sun is a visibly more vibrant shade of yellow.

I think the bottom of the base was originally glued in place, but that glue has weakened with age (or sun) and could be easily pried apart.

A small solar cell feeds into a circuit board, home to just two components: an electrolytic capacitor and a chip under a blob of epoxy. A coil wound from super fine copper wires is attached to this board as well. As explained in the Hackaday link above, this coil is both input and output: for sensing position of the magnet and for creating a magnetic field to boost the magnet’s swing.

The coil looked off-center, so I broke off the rear side of the base and reinstalled it to verify the coil is indeed off center when the magnetic pendulum (black plastic with black magnet on the bottom) is at rest. There is only about a millimeter of air between the coil and the magnet, a much closer distance than found in the cat mentioned in the Hackaday post.

This old dancing duck has a bit of arthritis and could not self-start under indoor light. I gave the pendulum a small tap and it started rocking but halted again after a few seconds. We can see the problem in the pivot point, which was designed to minimize friction. The pendulum axle has a triangular profile, so only a tiny sharp point touches the circular hole in the base. Years of dancing in the sun has worn both components. The triangular wedge’s sharp edge has been rounded off, and the hole perimeter is no longer circular. Together these two parts presented too much friction for the pendulum to overcome.

Daiso has long since stopped carrying this device, and I had no luck finding an exact replacement. There is no shortage of solar-powered dancing ducks for sale, but they all looked different from this cute little thing. Some are the opposite of cute, and a few looked downright scary! I have to say goodbye to this dancing duck now, it gave its all for dance and was quite an entertaining $1.50 spent.

Fundraising Keychain LED Flashlight

Sometimes an organization will send a little gift in the mail accompanying a plea for donation. These small tokens are sent as a psychological tactic to generate a return that far outweigh their low cost. I’ve received things like address stickers, notepads, and the occasional calendar. And now, I can add “keychain LED flashlight” to the list.

This item was included in a request to donate to Doctors without Borders, a well-respected organization well worth donating more money to. Whether they sent me a keychain flashlight or not. But it is on the teardown bench because I’m curious about the implementation details of a freebie giveaway that must have been designed for the lowest possible cost.

A power switch slider illuminates the commodity 5mm white LED. Judging by the exterior, I expect to find a LED and a coin cell battery inside, based on the width probably a CR2032 or CR2035. The power switch would have been designed to open/close the circuit with minimal parts. I see a seam on the side of the device, so the silvery plastic body must consist of at least two pieces. The switch would be the third silvery plastic piece. White plastic on top and bottom may be two pieces or a single piece. So not counting the keychain itself, I expected five pieces of plastic plus the LED and coin cell for seven parts.

My expectations were proven wrong as soon as I removed the first piece. White pieces top and bottom were indeed separate pieces, held together in a friction fit. A good friction fit requires tight tolerances which costs money. I had expected cheaper loose tolerances which would have meant holding things together with glue, but this wasn’t glued together.

Once I removed top and bottom white plastic pieces, rest of the flashlight was easily disassembled. Power comes from a trio of tiny LR621 coin cell batteries, not the single CR2035 I expected. As a result, there was more empty space inside than I had expected including an empty rear cavity that is big enough to hide a microSD card or three. The power switch was indeed a clever mechanism, but it required an extra piece of metal that I thought it might have done without.

This little LED flashlight was indeed an extremely simple and low-cost device, just not quite as simple or low cost as I had thought it would be. Nice to see my assumptions proven wrong.

RGB LED Fan Hub and Remote (Asiahorse Magic-i 120 V2)

I bought the Asiahorse Magic-i 120 V2 package from Newegg, which bundled three 120mm fans with embedded RGB LEDs with a hub and a remote to control those LEDs. Now that I have successfully created a control circuit for my own independent control of those fans and their LEDs, I no longer have any use for the hub and remote.

The remote has an array of 21 membrane buttons. Across the top, we can turn the LEDs “On” and “Off”. “Auto” will start running an animated pattern. Just below the “Off” button are brightness controls. S+ / S- controls the speed for animations, and M+ / M – cycles through different animated patterns. Bottom 12 buttons will show the selected solid color.

Top membrane is held on with moderately strong adhesive that could be peeled off, exposing the less interesting side of its circuit board.

Flipping the board over showed a single chip with its support components. There were no visible markings on the chip. Battery contact springs are at the bottom, the top features an infrared remote control LED emitter, and a few passive components in between.

After disassembling the remote, I started on the hub.

There were no exposed fasteners top or bottom. I pushed on the bottom sticker and felt the corners move.

The bottom sticker is glued on more tenaciously than the remote membrane keyboard and refused to come off cleanly. But at least those four Philips head fasteners are now exposed.

Not much to see on the bottom.

Flipping the circuit board over exposed… not many more chips than the remote. Most of the surface area are consumed by connectors all around the perimeter, and traces to connect them.

I’m glad to see fan connector pin labels are consistent with my reverse-engineered pinout table. A large component on this board appears to be a power transistor. I probed its pins and one of them is connected to all “F-” pins, so it is present for fan control. There are three sets of unused pads across the middle, provision for WS2812 LEDs wired in parallel with the fans. These three are chained together, left-to-right, with the leftmost LED receiving the same “DI” (data input) as all fans. When present, these three LEDs would act identically to first 3 out of 12 LEDs on board each fan.

There were a few other unpopulated pads on this circuit board, but there is one part I found fascinating for its absence: an infrared receiver like the one I found in a Roku. I don’t see one, and I don’t see solder pad provision for one. How could the hub receive IR remote signals without one? I know the remote and hub works together, so does this mean they communicate by radio frequency instead of infrared? I don’t know enough about RF circuits to look for components that would implement such a thing. I had thought all RF devices sold in the United States are required to have an FCC ID printed on it, but none are visible. Perhaps certain unlicensed frequency bands are exempt from FCC ID requirement? Shrug, doesn’t matter to me anymore as I won’t be needing this remote or hub to put their associated fans to use.

FormLabs Form 1+ Galvanometer Power Failure

I tried to revive a FormLabs Form 1+ resin printer that had been sitting unused for years, but the test print was a failure. Comparing against videos on YouTube showing a Form 1/1+ in action, I noticed two differences. First, the resin vat tilting action (to peel it off a print between layers) was not happening. And more seriously, the laser beam was not moving around to trace out the shape. Instead, it stayed focused on one spot solidifying resin and damaging the resin vat at that point. There are four mechanical actuators on this device: the vat tilt stepper motor, X/Y-axis galvanometers (shortened below to galvos), and the Z-axis stepper motor. Out of four, three aren’t working! Quite disappointing, but at least they should be electromechanical issues that I have a better chance of fixing than software issues. I’ll take it apart and look around.

My disassembly was guided by Bunny Studios’ Form 1 teardown blog post from almost ten years ago. I was glad for the reference, but as the blog post pointed out, FormLabs designed the machine for easy disassembly, inspection, and repair. All fasteners are easily accessible and use the same 2.5mm hex key.

Once I got to remove the back panel, majority of control circuitry became accessible. Only one circuit board is not visible in this picture, as it is mounted in the front for power button and screen.

The large horizontal circuit board has a power-handling section to the right, as indicated by the presence of many transistors, diodes, and inductors. To the left is the brain, including a SanDisk 4GB SD card that wasn’t accessible until the back panel was removed. The smaller vertical circuit board on the right is dedicated to X/Y position control, judging by cables connecting it to the X/Y galvos.

This printer had been shipped around without its original packaging materials, so I had hoped the problem was as easy as a loose connector I could plug back in. Thus my attention was immediately drawn to headers on these circuit board without a wire, but there were no candidate loose wires to plug into those headers. Apparently FormLabs has intentionally chosen not to use those connections, likely related to changes from original Form 1 to this Form 1+.

One of the unused connectors was labeled GALVO Y POWER. I see cables on GALVO Y SIGNAL and GALVO X SIGNAL as well as GALVO X POWER. I guess both galvos are powered from GALVO X POWER cable. This might be relevant to what I find later.

Disappointed that I didn’t find a loose connector I could plug back in or any other obvious easy-to-fix problems, I proceeded to unplug and reinstall every connector to reseat them. Working from left-to-right, everything looked and felt fine until I unplugged the right-most galvo connector. Once it was removed, I got a clear view of the galvo power connector below it.

Discoloration from overheating and possibly soot from a small fire. The toasty connector is the other end of GALVO X POWER. I don’t know enough about this device to say sharing X and Y galvo power from a single connector caused the failure, but it certainly looks suspicious.

I saw no obvious places where GALVO Y POWER could have connected to this galvo control board. I guess it is a later revision that integrated both galvo controls on a single board powered by a single cable. Compare this to Bunny’s earlier device, where we see two separate and seemingly identical galvo control boards, one for X and one for Y, each with their own power and signal cables.

This device is long out of warranty, and official support ended in 2017. I don’t expect FormLabs to have a replacement galvo control board for this Form 1+, but it wouldn’t hurt to ask and see what they say.