Staying on the theme of lights and switches, I have a sequel to my previous household light switch teardown: a double switch! This unit was retired and replaced by a new unit once one of the two switches (the lower one) could no longer stay off.

On the left, both switches are in their “On” position, and this is fine. On the right, top switch is in the proper “Off” position, but the lower switch could not do the same. If I flip the lever to “Off”, it doesn’t stay there but would move back a bit. Sometimes that’s still electrically off, which is fine. Sometimes it springs back to electrically on and I have to try again, which is annoying. But the real problem is the rare case when it stops in an unfortunate middle ground, and I can hear a lot of popping noises consistent with sparks/arcing inside the switch. Very bad! I replaced it promptly to avoid risk of permanent electrical damage. After it was replaced, I want to see exactly how the switch mechanism failed.

On the back side of this unit is a rivet-like structure, surrounded by text PAT PEND (patent pending?) and SPEC GRADE. I have no idea what spec it met the grade for, but I know this rivet has to go.

After drilling it out, its front facade was still held by four plastic clips. When I pried that face open, it was a sudden release and everything flew apart. Several pieces of metal landed at various places on my workbench. I think I found them all, but where did they used to live, and what were their function?

Two large pieces remained inside. They look like they carried power, with a rounded contact pad at the end. Two of the metal pieces that fell out have matching contact pads and wiring screw terminals, they must make up the rest of the power-carrying circuit. The lower pads are more charred-looking than the top, consistent with suffering a few arcing episodes, but other than that both sets look identical and would not explain the problem.

My hint came from looking at the lever’s back side. There are actually two levers sticking out. The shorter wider portion pushed on the large electrical bar, and the longer narrower portion pushed on something else. Process of elimination says it must be the two remaining pieces of metal that fell out.

Those narrow pieces of metal must have mounted to the side of the enclosure on their flat ends and acted as springs that held the lever in one position or another. When holding their flat ends together on the tabletop, one of them is visibly more tired. The weaker spring could no longer hold the switch lever in the off position.

So the switch was electrically fine, it was just a worn out lever spring. Would it have resumed working if I could manually bend the spring back and reassemble the switch? Maybe, but this double-switch was not designed to be repaired. After I drilled out the center rivet there was no secure way to put it back together safely enough for use.

It’s fine, it served its purpose over many years. And amusing enough, its replacement served one final purpose: letting me know my UPS batteries are no good and I need to buy replacements.

I am taking apart an Aurum motion sensing light fixture because its sensor and control circuitry has been damaged by water and no longer performs correctly. The pair of lighting modules still light up on command, though, so I’m hopeful I can find another use for them elsewhere. Let’s see what’s inside.

Based on my understanding of the sensor circuit, each of these two pods are capable of functioning as standalone 120V AC lights. White wire for neutral, black wire for live, and green wire for ground.

Supplying power lights up this little yellow circle of bright white LEDs, roughly one centimeter in diameter. It’s such a small surface area for a bright light source, especially relative to the volume of the rest of this pod. What is all that volume used for?

Like the sensor pod, a single fastener holds the elbow joint together and is easily disassembled.

Next is a trio of fasteners, easy enough to remove to let us see what’s inside the cylinder.

The answer: mostly air.

I had expected to see some AC to DC power conversion circuitry and was surprised to see such emptiness. The ground wire screws to the metal enclosure, but the live and neutral wires kept going to the front of the pod. There’s nothing else except access to three more screws.

Loosening those three screws released the front of the pod.

The plastic front was originally clear, but now yellowed and clouded with age. Moving it out of the way gives us a clear look at the LED array.

Cranking my lens to “Super Macro” mode enabled this picture, showing an array of 6 * 7 = 42 LEDs all wired in series. That would require north of 120V DC to drive, a pretty close match for rectified 120V AC. But I haven’t seen that rectifier yet.

Removing the oval plastic cover revealed this LED module in COB (chip on board) form factor. Made by Paragon LED, this compact circuit board accepts 120V AC power directly on its pads labeled L (line) and N (neutral). From there it takes care of everything else necessary to convert that power to light.

The second-biggest module (after the LED array itself) is this BT10S rectifier from HY Electronics, converting 120V AC power to DC and sending it onward to the LED driver somewhere under a black blob.

The Paragon LED module is fastened to the metal can with a gray square of soft sticky material. This must be a thermally conductive adhesive pad. And thus I have my answer to why we need a big metal can to support less than one square centimeter of LED: the COB needs a hefty heat sink.

Now that I have my answer, the next question is… what do I do with it? I don’t know yet, but I can write down some notes about the constraints involved.

I took apart a retired motion sensing light and found far more electronics components than I had expected to see inside the sensor pod. The complexity places it beyond my ability to trace through and draw up a KiCad schematic, but I still want to take a look to see what I can decipher.

At a high level, it looks like one board handles the 120V AC power with a relay and the other board handles sensing and sensor logic. Four wires connect between them.

Looking at the front of the power board, the black wire is incoming 120V AC line, red wire goes out to light pods. The two white wires, one incoming and one outgoing, are 120V AC neutral. This confirms the sensor pod only switches AC power. Converting AC power to DC voltage to drive LEDs are handled elsewhere inside the light pods. There are only a few components on this side, dominated by an AFE BRD-SS-124LM relay. Surrounding the relay are what appears to be a resistor, two capacitors, and a 4-position connector to the logic board.

Looking at the back of the power board, I can see both neutral wires are wired together. Looking at AFE Relay’s product information for BRD series footprint, I can see the relay will connect/disconnect between the black and red wire for 120V AC line power. This is the business end of the sensor pod and determines whether the light pods receive 120V AC power or not

Beyond that, I’m lost. I had expected to see a transformer to turn 120V AC into a lower voltage, followed by a rectifier to turn AC into DC suitable for a digital logic board. I definitely don’t see a transformer here, and I don’t see a rectifier module. These small red things labeled with D are probably diodes, do they implement a diode bridge? If there’s no voltage reduction, does it mean 120V go all the way to the sensor logic board? Maybe looking there would help me understand what’s going on.

Here’s the sensor logic board with the actual sensor itself front and center. U2 is a status LED. Potentiometer LUX SR1 adjusts level of light sensitivity, TIME SR2 adjusts how long the light should stay on after motion detection threshold has been triggered. The brown tint on the potentiometers are rust, result of rainwater intrusion. They would have been the closest components immediately below the broken sensor view window. Such exposure wouldn’t have done their electrical behavior any good.

In front of the sensor is a shiny bracket, dividing its field of view into thirds: left, front, and center. Here’s an oblique side view of the arrangement. I had hoped to read markings on this sensor so I could go look for a datasheet, but I saw nothing. Maybe it’s hidden by the shiny bracket? It might be plastic with a shiny coating, which I can cut away. If it is metal I doubt I could remove it without destroying the sensor module.

And now, the star attraction: the unexpectedly complex sensor logic board. It’s a single layer board, so I noticed multiple zero ohm resistors used as an overpass over other traces. Lots of other nonzero resistors, capacitors, and diodes. I see three components labeled BR 34 and two labeled FR 33, short enough of an alphanumeric designation a search returned a lot of hits but none I recognized as relevant. The silkscreen designation for those components start with Q. Wikipedia page Reference Designator says Q are transistors.

Since it’s a single layer board with few components on the opposite side, there’s no need for side light trickery. Shining a light from behind is enough to highlight majority of copper traces on this board.

One way I try to orient myself on the nature of a circuit board is to look for the big brain in charge of the operation. If I can find a datasheet for the microcontroller, there’s usually a section about the intended market for the device, the peripherals it has to support that market, and have sample application schematics. The biggest chip on this board has a ST Microelectronics logo and markings 324 GZ17334. A search led me to LM324 series of quad op-amps. Not a microcontroller, and I see no other obvious candidates for one.

The lack of a microcontroller combined with the largest chip containing a set of op-amps imply this circuit board runs on analog logic. A field I know even less about, and marks the end of the road of what I can decipher about this circuit board today. I set it aside to focus on the LED lighting pods this circuit board formerly controlled.

I retired a motion sensing light because water got in the motion sensor pod and it stopped sensing motion like it’s supposed to. Now I’m taking it apart. This post focuses on the motion-sensing sensor section.

I cleaned everything before the teardown, so sun damaged caused the discoloration visible here. We can really see where this sensor pod was shaded by adjacent light pods and where it gets hit with sunlight. The mounting thread is pristine, as it was safely shaded by the sheet metal base.

A single screw holds the elbow joint together and is easily removed for disassembly.

The wrist joint is a different story. I see no visible fasteners and, to make things more complicated, it blocks one of two screws holding the sensor pod together. I’ll look at other parts of the sensor pod and come back to this headache later.

There are two adjustment knobs on the bottom of the sensor pod. Looking through the damaged sensor window, I can see they’re connected to rusty potentiometers inside. No fasteners or retention mechanism visible from here, so I’ll try giving it a hard yank.

Brute force pulls them out after overcoming a retention clip mechanism I couldn’t see before. There’s also a small soft translucent rubber band to mitigate water intrusion.

One of the sensor pod screws came out easily, but the other one is still blocked by the wrist joint I couldn’t open. I have no good ideas on how to access that screw, but looking inside the sensor window I could see where the screw threads into. I could use my Wondercutter to cut that off at the base. It should be able to cut this plastic but it can’t cut metal, so I referenced the removed screw length to know where to cut in order to avoid the still-installed screw.

Once cut, the pod opened to reveal far more electronics than I had expected. I thought this was one of those products where component count is squeezed to an absolute minimum. So I expected to see a single circuit board with a half dozen components. There are actually two boards separated by a piece of clear plastic, connected by a 4-wire cable, and I estimate several dozen components across both boards.

Two rusty screws held the front board in place, two more held the rear board in place, before everything came apart.

Now that I can look at the wrist joint from the inside, I can see there was no elegant way to remove it. I would either have to pull on it hard enough to overcome these one-way clips, or cut something. I guess I had accidentally stumbled into the least-cutting way to open this sensor pod.

The inside of the sensor window showed a series of ridges characteristic of a Fresnel lens, a feature I didn’t notice until I could see these pieces from their back.

I had hoped to find a simple circuit board I could understand. The unexpected complexity meant it was beyond my current skill level to decipher how everything worked, but I could still give it a try to see how much I could pick up.

After looking inside an unreliable power supply, I moved on to another piece of retired electrical equipment. This motion-sensing light (Aurum Electronics model number AEC-326KA2-AC14W) overlooked my back yard for several years, installed under eaves facing west. The roof shielded it from direct sunlight from morning to noon, but it would be under punishing Southern California sunshine in the afternoon until sunset.

Sun damage eventually cracked the motion sensor window, letting rain into the sensor pod. The damaged unit would illuminate when nothing is in the yard, or stay dark when there actually is something moving. (Usually me, frantically waving.) I’ve installed a new unit so this one is getting the teardown treatment.

First step is to clean up years of outdoor exposure. More than just dust, there are also carcasses of dead insects and streaks of bird poop.

Inside the base is fairly straightforward. Mechanically, we can see two identical metal nuts attaching each light pod. The third smaller plastic nut holds the sensor pod. The two light pods are made of metal, the sensor pod plastic.

Electrically, green ground wire is screwed to the base, then a green ground wire enters each of two light pods. Curiously no ground wire enters the sensor pod. 120V AC power wires neutral (white) and live (black) wires go into the sensor pod. Two other wires (white and red) come back out, which are crimped to wires going into each light pod.

I can think of two ways to implement this:

1. 120V AC power enters the sensor pod and is converted to DC power. The white and red wires coming out are DC power to run LEDs in each light pod.
2. 120V AC power enters the sensor pod and is switched there. The white and red wires coming out are still 120V AC. Conversion to DC to run LEDs are done inside each light pod.

Which of these two guesses was correct, or perhaps it was yet another way I hadn’t thought of? I know of one way to find out.

Since each attachment point is fastened by a large hex nut, turning them counterclockwise was enough to disassemble this motion sensing light into its component modules: two light pods, one sensor pod, and the base which is now just an empty metal shell. I’ll look at the sensor pod first.

I’ve just disposed of two salvaged cooling fans, and now I’m going to pick up a bigger one.

This Thermaltake power supply unit (PSU) was retired because it would turn on and run for only a short time (less than ten minutes, sometimes only a few seconds) then the computer would shut down. The fan turns, so it’s probably not simple overheating. Since it turns on, it’s not as simple as a blown fuse. But at least it didn’t fill my room with smoke, so that’s good.

It’s a shame this PSU died because it’s got nice specs, along with the convenience feature of modular connectors reducing wiring clutter inside the case.

Six screws held two halves of the enclosure together. Once removed I could slide them apart.

The 140mm fan is connected via a commodity JST-XH header, making it easy to repurpose.

This 140mm fan is larger than the 120mm fan I had just worked with, which on paper moves more air even as the fan turns at a slower (and thus quieter) speed. I’m curious to see if it is true, but I have to find a place for it first. This will be my first 140mm fan and I’m not sure what I’ll do with it just yet.

Here’s an inside view of those modular connectors, implemented as a collection of circuit board connectors. The power wires leading to this connector board is very hefty. Lettering on the insulation says 12AWG.

There were no obviously failed components inside this PSU.

And I see no obviously burned traces on the back of the circuit board. It’s a shame a high-spec PSU had to be retired, but I don’t like to take the risk of unreliable power. Bad power could damage far more expensive components (CPU, GPU, SSD) plus the annoyance factor of a computer that randomly shuts down. It’s just not worth it.

After I installed a working fan in a power supply, I had two broken 120mm 12VDC fans on my hands. One with a bad bearing which needed replacing, and another one which was going to be the replacement until my clumsiness destroyed it. I’ve taken apart similar fans before so I didn’t expect any surprises, but it’s always interesting to see how different companies solve similar problems.

The fan with growling bearing is by Yate Loon Electronics. It’s very hard to read very much more detail out of the label because its center has been distorted into a faded shiny bubble. I presume this is result of friction heat generated by the failing bearing.

Back of the label is consistent with heat damage. I had expected to see the motor shaft at this point but there’s a soft red rubber seal I had to remove first.

There’s plenty of lubricant visible, too bad none of this was in the right place to do much good.

Popping off the white plastic split ring allowed the fan to come apart. I saw no visible wear to explain the noise this fan had been generating. At some point in the future I hope to have the knowledge to know what to look for, which may require magnification equipment.

A closer view of the core of the fan. It is securely fastened to the plastic base.

I found no fasteners or clips to release, so I went with brute force: using large pliers to rip the core off the base to see the back of the circuit board.

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The other fan was functionally fine until I accidentally broke a fan blade. It was made by Poweryear and they have no fault for this. It was entirely my clumsiness.

Under the label was a hard plastic seal. I was surprised to see this, it meant I could not access the plastic split ring (or functional equivalent) to disassemble the fan.

I went straight to ripping the core assembly off the chassis, unintentionally breaking another fan blade in the process. I still couldn’t get to the back side of this fan’s axle. Teardown foiled!

No matter, sleeve bearings fail and I’m sure I’ll have more dead 120mm cooling fans in the future. For now I can harvest my first 140mm fan from a misbehaving power supply.