Using TCL 55S405 TV as Computer Monitor

I just bought a LG OLED55B2AUA for my living room, displacing a TCL 55S405. I have several ideas on what I could do with a retired TV, and the first experiment was to use it as a computer monitor. In short, it required adjusting a few TV settings and even then, there are a few caveats for using it with a Windows PC. Using it with a Mac was more straightforward.

As expected, it is ludicrously large sitting on my desk. And due to the viewing angles of this (I think VA) panel, the edges and corners are difficult to read. I see why some people prefer their large monitors to be curved.

I noticed a delay between moving my mouse and movement of onscreen cursor. This delay was introduced by TV’s image processing hardware. During normal TV programs, the audio can be delayed in order to stay in sync with the video. But that trick doesn’t work for interactive use, which is why TVs have a “Game Mode” to disable such processing. For this TV, it was under “TV settings” / “Picture settings” / “Game mode”. Turning it on allowed the mouse to feel responsive again.

The next problem was brightness. Using it as a monitor, I would sit much closer than I would a TV and there is too much light causing eyestrain. First part of the solution is to choose “Darker” option of “TV settings” / “Picture settings” / “TV brightness”. Then I went to “TV settings” / “Picture settings” / “Fine tune picture” where I could turn “Backlight” down to zero. Not only did this make the screen more comfortable it reduced electrical power consumption as well.

According to my Kill-A-Watt meter, this large TV consumed only 35 watts once I turned the backlight down to minimum. This is actually slightly lower than the 32″ Samsung computer monitor I had been using. Surprisingly, half of that power was not required to run the screen at all. When I “turn off” the TV, the screen goes dark but Kill-A-Watt still registered 17 watts, burning power for purposes unknown. Hunting around in the Settings menu, I found “System” / “Power” / “Fast TV Start” which I could turn off. When this TV is no longer set for fast startup, turning the TV off seems to really turn it off. Or at least, close enough that the Kill-A-Watt read zero watts. This is far better than my 32″ Samsung which read 7W even in low-power mode.

Since this is a TV, I did not expect high framerate capabilities. I knew it had a 24 FPS (frames-per-second) mode to match film speed and a 30 FPS mode for broadcast television. When I checked my computer video card settings, I was pleasantly surprised to find that 60Hz refresh rate was an option. Nice! This exceeded my expectations and is perfectly usable.

On the flipside, since this is a TV I knew it had HDCP (High-bandwidth Digital Content Protection) support. But when I start playing protected content (streaming Disney+ on Microsoft Edge for Windows 11) the TV would choke and fail over to its “Looking for signal…” screen. Something crashed hard and the TV could not recover. To restore my desktop, I had to (1) stop my Disney+ playback and (2) power cycle the TV. Not just pressing the power button (that didn’t work) I had to pull the power plug.

The pixels on this panel were crisp, and 4K UHD resolution actually worked quite well. 3840×2160 resolution at 55″ diagonal works out to 80 DPI (dots per inch), which is right within longtime computer monitor norms. For many years I had used a 15″ monitor at 1024×768 resolution, which worked out to 85DPI. Of course, 80DPI is pretty lackluster compared with “High DPI” displays (Apple “Retina Display”, etc.) now on the market with several hundred dots (or pixels) per inch. Despite crisp pixels at sufficient density, text on this panel isn’t always legible under Windows because it doesn’t work well with Microsoft’s ClearType subpixel rendering. ClearType takes advantage of typical panel subpixel orientation, where the red/green/blue elements are laid out horizontally for each pixel. This panel, unfortunately, have its elements laid out vertically for each pixel, foiling ClearType trying to be clever. In order for this panel to take advantage of ClearType rendering, I would have to rotate the screen 90 degrees to portrait orientation. This isn’t terribly practical, so I turned ClearType off.

For comparison, a brief test with my Apple MacBook Air (M1) saw the following behavior:

  • Same 3640×2160 resolution and 60Hz refresh rates were available.
  • I could activate HDR mode, an option that was grayed out and not available with the NVIDIA drivers on my Windows desktop. I lack MacOS HDR content so I don’t know whether it actually works.
  • Streaming Disney+ on Firefox for MacOS showed video at roughly standard-definition DVD quality. This is consistent with behavior for non-HDCP displays, and much preferable to crashing the TV so hard I need to power cycle it.
  • MacOS font rendering does not use color subpixels like Microsoft ClearType, so text looks good without having to turn off anything.

It appears this TV is a better monitor for a MacOS computer than a Windows machine.

LG OLED Look Gorgeous But webOS Is Horrid

Thanks to Black Friday discounts, I acquired an OLED TV which I had coveted for many years. I decided on a LG OLED55B2AUA purchased through Costco (Item #9755022). LG’s “B” line sits between the more affordable “A” and the more expensive “C” lines and it was a tradeoff I liked. (There are a few additional lines higher than “C” priced above my budget.) The TV replaced a TCL 55S405 and while they are both 55″ TVs, there is a dramatic difference in image quality. There are reviews out there for full information, my blog post here concentrates on the items that mattered to me personally.

The Good

  • The main motivation is image quality. OLED panel advantage comes from their self-illuminating pixels leading to great contrast and vibrant colors. The “C” line uses panels with a higher peak brightness, but I haven’t found brightness lacking. When the filmmaker intentionally includes something bright (flashlight in a dark room, etc.) this “B” panel is bright enough to make me squint.
  • HDMI 2.1 with variable refresh rate capability and a higher maximum frame rate (120FPS) so I can see all the extra frames my new Xbox Series X can render. On this year’s “B” units, HDMI 2.1 is supported on two of four HDMI ports, which is enough for me. HDMI 2.1 is supported on all four ports of “C” line, and none of “A” line because they are missing high framerate features entirely.
  • The LG “magic remote” has an accelerometer to let us move an on-screen cursor by tilting the remote. This is far better than the standard up/down/left/right keypads of a TV remote and, combined with responsive UI, makes navigation less of a chore. This is the only good thing about LG’s user interface.

The Bad

For reasons I failed to diagnose, the TOSLINK output audio port could not send sound to my admittedly old Sony STR-DN1000 receiver. Annoyingly, LG designed this TV without analog audio output. Neither a headphone jack (as is on my TCL) nor classic white and red RCA audio jacks. In order to use my existing speakers, I ended up buying a receiver with HDMI eARC support. This is money I would have rather not spent.

The Ugly

The internal operating system is LG’s build of webOS, which they have turned into a software platform for relentless, shameless, and persistent monetization efforts. My TCL Roku TV also served ads, but not nearly as intrusively as this LG webOS TV. That powerful processor which gave us snappy and responsive user interface isn’t going to just sit idle while we watch a movie. Oh no, LG wants to put it to work making money for LG.

Based on the legal terms & conditions they wanted me to agree to, the powerful processor of this TV wants to watch the same things I watch. It wants to listen to the audio to listen for keywords that “help find advertisements that are relevant to you”. That’s creepy enough, but there’s more: it wants to watch the video as well! The agreement implies there are image recognition algorithms at work looking for objects onscreen for the same advertising purpose. That’s a lot of processing power deployed in a way that provides no benefit to me. I denied them permission to spy on me, but who knows if they respected my decision.

Ad-centric design continues to the webOS home screen. The top half is a huge banner area for advertisement. I found an option to turn off that ad but doing so did not free up space for my use. It just meant a big fixed “webOS” banner taking up space. Next row down, the leftmost item represents the most recently used input port, which in my case is the aforementioned Xbox Series X. The rest of that row are filled with more advertising, which I haven’t found a way to turn off. The third and smallest row includes all the apps I care about and even more that I did not. Overall, only about 1/8 of the home screen surface area are under my control, the rest paid LG to be on my home screen.

I’m frankly impressed at how brazenly LG turned a TV into an ad-serving spyware device. I understand the financial support role advertisements play, but I’m drawing a line for my own home: as long as the ads stay in the menus and keep quiet while I’m actively watching TV, I will tolerate their presence. But if an LG ad of any type interrupts my chosen programming, or if an LG ad proved they’re spying on me despite lacking permission, I am unplugging that Ethernet cable.

UPDATE (two days later): Well, that did not take long. I was in the middle of watching Andor on Disney+ (Andor is very good) when I was interrupted by a pop-up notification on the bottom of the screen advertising free trial to a service I will not name. (Because I refuse to give them free advertising.) I will not tolerate ads that pop up in the middle of a show. Struggling to find an upside I can say this: that advertised service appeared to have no relation to Disney+ or anything said or shown in Andor, so the ad was probably not spying on me.

I was willing to let LG earn a bit of advertising revenue from me, as Roku did for my earlier TV, but LG’s methods were far too aggressive. Now LG will earn no ad revenue from me at all because this TV’s Ethernet cable has been unplugged.

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:

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.

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.

Waterpik WP-150W Teardown

My normal home dental routine includes daily Waterpik cleaning, which has been great for my teeth but there’s a cost. Water and electrical mechanics do not peacefully coexist (just ask anyone who owns a boat) which might be why my Waterpik machines haven’t lasted very long. A few years ago I took apart a battery-powered Waterpik that had died, today I am taking apart another.

This one is powered by household AC and it hasn’t quite died. However, it is noticeably less powerful than it used to be. When it was too weak to dislodge a piece of food wedged between my teeth at maximum strength setting, I replaced it with a new unit to restore full teeth-cleaning power. I want to see if I can find any sign of wear and tear that would explain the reduced strength.

An electrical appliance that has water running through it is definitely presents a risk for electrical shock! I’m going to disregard the warning on this bottom label and open it anyway, as I don’t intend to put it back together or run water through it again.

Adjacent to the label is a socket for the handheld wand. Removing the plug unveiled a rubber O-ring seal, which was expected, and this tan-colored flap of plastic, which was unexpected. I see a mesh texture that made me think it might be some sort of filter, but it is not a mesh and seems fully watertight. My best guess is some sort of backflow prevention.

I didn’t expect to find much inside the handheld wand, but I cut it open anyway to confirm. The on/off water flow valve seems fine and there’s no sign of obstruction.

Returning to the base, I removed four Philips-head fasteners between base and enclosure. The strength adjustment knob also had to be pulled out before the enclosure can move.

Inside the enclosure we see a black cylinder where water is fed from a reservoir, and we can see a bit of orange colored sealant to make the joint watertight. The gear-looking thing is for the power switch. It looked and felt like a rocker switch, but it actually has this rack-and-pinion mechanism to translate the rocking motion to a linear sliding switch. If the designers wanted a rocker switch, why didn’t they use an actual rocker switch for household AC? This mechanism feels like unnecessary complexity.

We also see signs of a fine black dust/powder inside, more details on that shortly.

After the sliding switch, AC power is fed through an array of diodes for rectification. A big capacitor smooths output and a resistor drains residual charge from the capacitor after use. The strength knob has no involvement in the electrical side at all, the motor runs always runs at full speed and jet strength is a strictly mechanical affair.

I had expected the power to go straight into an AC motor, but that rectifier circuit was necessary as this is actually a 120V DC motor. Something about this DC motor was worth adding the cost of rectification circuit board, I’m curious what tradeoffs are involved.

A disadvantage of DC motors is the need for commutator and brushes, which wears over time. That black dust deposited all around enclosure interior are little bits of vaporized motor brush and commutator flowing out of the motor like smoke, as we can see here. Worn commutator/brushes is the first visible candidate explanation for reduced strength of this device.

Here is the jet strength adjustment mechanism. The spring-loaded gasket at the bottom pushes against the adjustment disc, which has a thin groove through it. It looks like turning the dial adjusts how much of the thin groove is presented to water flow, sapping its strength on longer journeys.

But that is only a guess, because I’m not confident I understand how this system works. Here is the water reservoir intake assembly, which presents two paths for water coming in from the reservoir. One through the holes at the side of a narrow neck, and the other through a spring-loaded contraption for purposes I don’t understand. Once this assembly was removed, I could see the intake tube actually goes all the way through to the exit for the handheld wand.

For the Waterpik to function, all of this must implement a system to ensure one-way flow of water, but I have trouble visualizing how the hydrodynamic forces would interact to make that happen. Disassembling the spring-loaded contraption got me no closer to illumination. Somewhere in here might be the answer to reduced strength as this device aged, but I couldn’t begin to guess how.

The water-pumping piston assembly was relatively straightforward. Motor shaft output is geared down to a crank to move the piston back and forth through its cylinder. No signs of water intrusion and all the lubricants still in place explains why there are no signs of wear or play in the mechanism. Whatever caused this Waterpik to weaken over time, it’s probably not here.

The best hypothesis so far is wear and tear on DC motor brush and commutator. I want to open it up for a look, but the motor is held by these metal tabs bent from the motor can. Roughly one millimeter of steel is too stout for me to bend out of the way with pliers.

Which means it’s time for the Dremel cutting disc!

Once those two tabs were cut out of the way, I could remove the white plastic end cap and see the motor commutator and brushes. They are very definitely worn, but I wouldn’t have expected this level of wear to cause a severe degradation in output power.

This Waterpik base managed to keep a few a secrets even when disassembled. I still don’t understand the complexity of how water flow is restricted to be one-way, and I failed to find an obvious explanation for a weak output jet. At the rate I’m wearing them out, though, I’m sure I’ll have another opportunity in a few years.

Black & Decker Clothes Iron (IR0175W)

The main job of an iron is to make a flat piece of metal hot so we can use it to flatten wrinkles in our clothes. This particular iron was retired when it could no longer reliably do that one job. When plugged in, it would get hot as expected. Once it reached a certain temperature, it would slowly cool down, which is also expected. But it failed to turn the heat back on quickly. This iron would cool to almost room temperature before it would heat itself back up. I tried to find other use for it, but I’ve decided to take it apart. If I can fix it great, if not I will dispose of the remains.

No manufacturing date was visible on the product label. We see the old Black & Decker logo and searching for this model number IR0175W returned no results. Judging by appearance I would guess it is roughly twenty years old, because Apple made this “Bondi Blue” color cool in 1998 with the original iMac. Within a few years, everything made of plastic was available in this shade of translucent blue alongside white plastic.

The only externally visible fastener was a Torx 10 screw just below the power wire. It’s even a “security” Torx with a little post in the middle. It was quickly dispatched so this back plate can be removed revealing ordinary Philips head fasteners for the remainder of this teardown. “This would be easy!” I thought.

I was sadly mistaken. I couldn’t figure out how to remove the top plate elegantly and resorted to brute force. After it was torn off, I saw it was secured by a Philips fastener that was hidden under the steam pump button. (See green rectangles in above picture.) This button had plastic clips so that, once installed, it could not be removed. I see no way to open this without damage. This external enclosure is ruined, I’m not going to be able to fix it and put it back together.

The circuit board in the handle is interesting. It had 120AC line (red, labeled L AC2) and neutral (blue, labeled N AC1) coming in, and an output line (yellow, labeled OUT). The yellow and blue wires connect to the body of the iron, so this blue rectangular relay is definitely capable of switching the heat on or off. However, it is not in charge of temperature control, because there is no way for it to sense the current temperature or read the user adjustable temperature setting dial. This circuit board does have a mechanical sensor of some sort in the black rounded enclosure visible just to the right of the blue relay. It makes sounds when I shake it that is consistent with a little metal ball inside. I hypothesize this circuit implements the safety timer. If no motion is sensed over a time period, turn off the heat.

Removing the top deck and temperature dial revealed the Bondi Blue water reservoir. We can see the top end of the temperature regulation mechanism where it connected to the temperature dial.

Not much new is revealed once the water reservoir was removed. I was amused to notice that the reservoir was installed incorrectly at the factory. We can see the orange water gasket leading to the hot bits was crushed out of place for roughly one quarter of its perimeter. Thankfully I never noticed a leak from this error, though I didn’t use the steam function very much anyway.

The bottom-most layer in this stack: Heating elements permanently enclosed and bonded to the metal ironing surface. The temperature regulation system is fastened to the top of this layer.

Temperature regulation is a mechanical system centered around a bimetallic strip. Simple in theory: the circuit is closed to heat things until the strip changes its shape and opens the circuit. The system closely cools until the strip changes its shape again to close the circuit and repeat the process. Turning the heating level knob (top layer) I see it is a threaded contraption that ends in a white insulator point pushing on the second layer. Turning the dial subtly changes the bimetallic strip assembly geometry so it changes shape at different temperatures.

I turned the dial back and forth through its range of motion (~270 degrees) and I could see and hear the bimetallic strip pop back and forth. I did this a few times before I realized… wait, that’s not supposed to happen! This thing is at room temperature. A clothes iron shouldn’t be turning its heating element off at room temperature. This behavior is consistent with the observation this iron cools off too much before heating back up. I assert this bimetallic strip should remain at the closed position through the entire range of this dial at room temperature. But the only candidate for adjustment is a tiny flat head brass screw at the top of the dial, securely fastened by a blob of adhesive. I managed to damage the brass before I made any progress breaking that adhesive blob, ruining my chances of fixing it. This teardown was instructive but ultimately a failed repair. I disposed of the remains and moved on to the next teardown.

Evaporator Fan Motor (ADL-5846AMEA)

I took apart a microwave oven turntable motor and found it surprisingly simple. Encouraged, I dug through my “take apart later” pile for another appliance AC motor and found this item.

Sticker says:

2940rpm 0.14A
ADL-5846AMEA 12732601
115V 60Hz 4.6W Z.P CL.A
SUNG SHIN 030307

Searching for “ADL-5846AMEA” found this was an evaporator fan motor, meaning it was responsible for circulating cold air in a refrigerator. While we don’t care which direction a microwave turntable turns, the direction is very important for a fan motor. Given this fact, and assuming reliability and low cost would be the driving factors in the design, I had expected to find a shaded-pole motor inside this housing.

I was wrong! It was far more complex inside than I had expected. There are four distinct coils mounted to a circuit board with roughly a dozen other components. Through-hole capacitors and diodes are mounted on the same side as the coil.

The opposite side are mostly surface-mounted components, with two large prominent field-effect transistors (FET1 and 2). For me, the most unexpected component is the label box up top:


Wow, there is a Hall-effect sensor on this board, too?

There it is, nestled between but slightly offset from the center point between those coils. Its presence means this control circuit has feedback on rotational speed of this motor. This can be something as simple as detecting a stall, or as complex as variable-speed control. This motor has only two wires for power input, leaving no provision for communicating speed control. Therefore if the hall sensor is for speed control, that control logic must be completely encapsulated inside this module. But following copper traces failed to find anything that resembled a digital microcontroller. I guess it is a completely analog control circuit, which is indistinguishable from voodoo magic for my current level of knowledge.

Why would a refrigerator need such complexity in a fan motor? There must have been a requirement that was deemed more important than “lowest cost” and my best guess is efficiency. Wikipedia claims shaded-pole motors are only about 26% efficient, and the rest would have turned into heat. Waste heat is especially bad for an evaporator fan motor that sits in the cold loop of the refrigerator. Making this motor more efficient reduces workload on the cooling system, helping the refrigerator meet Energy Star and other similar requirements around the world.

The two motor shaft bearings would have been another tradeoff between cost and efficiency. The motor shaft has a bearing assemblies front and back to reduce friction, which reduces heat and increases efficiency. It is more complex than a simple oil-embedded metal sleeve bearing and less complex than a roller bearing. My fingers could feel that the soft absorbent pads are oily, but I’m not sure what I’m looking at. Are they intended to serve as additional oil reservoir for the metal sleeve? Or are they supposed to draw oil out of it? This evaporator fan motor teardown was full of surprises, from the control circuit board to this bearing assembly. I love it.

Microwave Turntable Motor (TYJ50-8A19)

Today’s teardown subject is a motor that once spun the turntable inside a microwave. Emily Velasco salvaged it from a broken microwave and reused it in a kinetic sculpture named Dark Star.

Sadly, Dark Star met an unfortunate end when it fell off the wall. Among the debris was this motor, its output shaft now severed. I asked for the damaged motor so I could see what’s inside.

Information was stamped into the front and back of this motor. I read the following information on the front:

Heng Xing
100/120V ~50/60Hz 4W4/4.8 R.P.M.

And on the back:


Since “TYJ50-8A19” was stamped on both sides of the motor, I used that for my online search. Multiple Amazon vendors offered to sell very similar but not identical motors(*) and there were eBay and AliExpress vendors as well. (Some even have metal output shafts, which might have survived the fall.) Most of the listings described them as microwave oven turntable motors, some listings even had explicit model numbers of microwave ovens that used this style of motor. I guess “TYJ50-8A19” was the model number used by a specific manufacturer, but it has since been copied by others and became a generic designation. (For another example, see 28BYJ-48 unipolar stepper motor.*)

Front face of this motor was held in by the outer casing pressed inwards at four locations. Bending those tabs out of the way freed the face, showing this geartrain. The lubricant in this gearbox seem to get darker and more viscous (thicker) as we go from motor rotor towards output shaft. I can’t tell if this is because multiple different lubricants were used, or if this is the same lubricant responding to different stresses in use.

Flipping over the broken output shaft, I see broken plastic on the back side as well. Given how low the costs are for these motors, I doubt I could find replacement gears. The strength and precision required to replace this gear is beyond what my hobbyist FDM 3D printer is capable of, so I can’t make my own. If I had a resin printer I could emulate the shape, but I’m not sure if hobbyist level resins are strong enough. Another concern is the lubricant, which might damage certain resins.

There were six moving parts in this motor: the output gear/shaft, the rotor with a ring of permanent magnet mounted to a blue plastic hub, and four gears in between them.

A metal plate in the middle of the motor held four metal pins acting as axles for each intermediate gear. The axle for the rotor is a similar metal pin mounted to the outer shell. The output shaft which I had expected to receive the most stress does not have a metal axle shaft, a curious design decision that probably contributed to this motor’s demise.

Below that plate is… a single coil? This was unexpected. From the Wikipedia article for synchronous motor, I had expected to see multiple coils. Most of my teardown experience to date have been with DC motors, so I didn’t know quite what to expect with this AC motor. Given its price I knew it had to be simple to manufacture, but I hadn’t known they could be quite this simple in construction.

If it is indeed a single coil connected directly to the single phase of household 60Hz 120V AC, it would generate a magnetic field that flips polarity at 60Hz. In theory I understand that’s enough to get a rotor turning, but with a single phase there’d be no control over which way the rotor decides to start turning. This fits with the “CW/CCW” stamped on this motor, and ideal for the microwave turntable use case where we don’t really care which direction it spins.

But to make it work, what kind of magnetic field does this rotor’s permanent magnet need? In my mental model, aligning the magnet’s north/south poles to the rotor axis wouldn’t impart a rotational force as the electromagnetic field oscillates, neither would aligning the poles perpendicular to the axis. Now I’m curious and I want to visualize this particular magnet. I could buy a sheet of magnetic viewing film (*), or some ferrofluid(*), or some iron powder/filings (*). Or perhaps I could make my own metal filings? That will be a project for another day. Right now, I want to build on this experience and take apart another appliance motor.

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

Microwave Water Heating Tests

Microwave ovens have become a fixture in kitchens, offering a convenient way to heat or reheat foods quickly and efficiently. Internet opinions on their expected lifespan range somewhere from seven to ten years. Recently, my reheated leftovers occasionally came out cooler than expected. Is my microwave failing?

As always, the first step is to find documentation. Looking at the manufacturer’s plate at the back, I find it is a Sharp R-309YK. A PDF manual for R-309Y model line is available for download from Sharp. (The “K” at the end designated the color, which is black in my case.) I had hoped the manual would have a “Troubleshooting” section, as appliance manuals sometimes do, but not this one. The identification plate also said the microwave was manufactured in December 2014. Since we’ve passed the seven-year anniversary, a failure would be unfortunate but not completely unreasonable.

Absent a troubleshooting section in the manual, I went online and found several tests for microwave effectiveness by heating water. In increasing order of credibility in my book, the results were:

Test #1: Wikihow = Fail

This test heats two cups of water on high for one minute and measures the temperature difference before and after. A healthy microwave is expected to raise the temperature by 35 to 60 degrees Fahrenheit. Using my food thermometer I measured the starting temperature at 64.9F, ended at 90.0F, for a rise of 25.1F. This is lower than the accepted range.

Test #2: GE Appliances = Pass

This test doubles the amount of water to one quart, and more than doubles the heating time to two and a half minutes. Despite proportionally longer heating time, this test had lower expectation on heating with a target range of 28 to 40 degrees Fahrenheit. My test started at 69F and ended at 34F, right in the middle of the target range.

Test #3: USDA = Pass

This test is a little different than the other two. The quantity of water is smaller: only one cup, but the heating procedure is different. Instead of measuring temperature rise over a fixed time duration, we are going from freezing to boiling temperatures and measuring the time elapsed. The water started showing small bubbles at two and a half minutes, and a full roiling boil at three minutes. Based on a lookup chart accompanying this test, this is consistent with a microwave in the range of 700 to 800 Watts. Lower than the advertised 1000 Watt but still within the usable range.

Result: Two Out of Three

My microwave passed two of three tests. Furthermore, since I place more credibility with USDA and GE than whoever authored the Wikihow article, I’m inclined to put more weight in those results. It appears that my microwave is functional, at least nominally. But then how might I explain the lower-than-expected heating I experienced?

Unknown Cycling

The best guess is a behavior difference I noticed during these tests. They are all heating water on high power setting, which means everything should be running at full power at all times. But during normal use, something is cycling on-and-off. I could hear a change in sound, and the interior light would flicker. The magnetron is expected to cycle on-and-off during a partial power reheat, but not when it is set to full power.

Looking online for potential explanations, I read the magnetron may turn off for a few seconds if it got too hot. This could happen, for example, when there’s not quite enough food in the microwave to absorb all the energy. If that was the case, however, I thought my food would be piping hot. My current hypothesis: something is triggering a self-protection mode during normal use, but not during these water heating tests. I’ll keep my eyes open for further clues on microwave behavior… and also keep my eyes open for discounts on 1000-Watt microwaves.