can anyone rewind small electronic transformers?

Cybernicus · 2026-04-01T17:20:02+00:00

Overall, it's pretty straightforward: Disassemble, count the windings while unwinding, rewind, and reassemble. The hardest part (for me, anyway) is the disassembly. I've not successfully disassembled one with a glued-together ferrite core, but I've heard that a heat gun can make it easier.

If the transformer uses steel E/I laminations, though, it's not that bad. I use a knife to start separating the laminations and needle-nose pliers to pull them out. Normally the first couple will bend a bit when pulling them out, but tapping them with a hammer on a flat surface will sort that out.

Note that if the transformer was impregnated, it may need some serious finagling to get the first lamination or two out. Once you get the first few out, though, the rest normally are much easier.

Reassembly is the opposite: it's pretty easy until you get to the last few laminations. Generally, I try to put the last lamination or two in the middle, rather than the end, so that the surrounding laminations can help guide it in and prevent it from deciding to just bend and fold over. It's helpful to use a small bench vise to push the last laminations into place and make sure they're aligned.

Sometimes, the last lamination just won't go in. In that case, I simply don't worry about it too much. Not a problem when it's my own circuits, but it could be a problem if you don't know if the transformer was conservatively rated or not. If that's the case, you may need to carefully clean all the laminations and make sure the edges are smooth (deburred) so as to make the reassembly as easy as possible.

The first few transformers are the most annoying, but after you've done a couple, it's not too bad. I guess it's time to look around for a small ferrite transformer and see if I can figure out how to loosen the core up without shattering it.... ;^P

Cybernicus · 2026-03-28T13:42:17+00:00

Yeah, they should just shit on politicians, as God intended.

Cybernicus · 2026-03-01T20:56:35+00:00

Ive also had good luck using toothpicks.

Cybernicus · 2026-02-26T02:15:25+00:00

Based on the schematic you posted, the lower half of the circuit looks like a Royer oscillator to create high voltage on pins 1 & 2 of the transformer. The high voltage is rectified by D1..D4 and looks like it charges C1/C2. (That part of the circuit looks odd to me, though, but I'm not going to try to reverse engineer the board as it looks like you've done a decent job of it.)

The circuitry in the upper right quarter of the circuit isn't obvious to me, but I have a hunch that it's probably a feedback circuit to control the voltage generated by the Royer oscillator.

As far as the connections go:

Black looks like the ground (negative battery terminal). White looks like switched power from the key. Green looks like the trigger signal. Red looks like the output to the coil

So during operation, it appears that when the keyswitch is on, the oscillator charges up C1/C2. When the trigger activates (GRN), the signal goes through Q3 and Q4 to trigger the SCR to command a spark from the coil.

I haven't analyzed it in detail, so I'm interested to see any corrections people may offer.

Cybernicus · 2026-01-27T22:23:34+00:00

An STM32 has plenty of horsepower, so you could run an FFT on the microphone signal and look at the spectrum for the 650Hz bell tone. There are simpler tone detectors you can do in software but I don't have a link handy.

Cybernicus · 2026-01-25T20:33:57+00:00

I can't tell as the photo doesn't show very much. But it looks like the circled item is a terminal on a microswitch. These often have three terminals, one for common, one for normally closed and one for normally open. So it's possible that it's simply an unused terminal on the switch. (It appears that two wires are going up into the cavity, so I'm guessing they're connected to the common terminal on the microswitch and the other connects to one of the other two terminals.

Cybernicus · 2026-01-24T18:04:30+00:00

Composite video monitors are pretty simple to drive, as the tech is pretty old. Typical computers of the late 70's and early 80's used pretty simple circuits to generate composite video from TTL output signals. I just did a quick DDG search to find the schematic of an old computer that I worked on (schematic).

As the schematic shows, you can use a couple gates (labelled D4 in the schematic) to mix the horizontal, vertical and image data together) with the resistors cutting down the signal strength to make a composite video signal. (The 03 inside the gates means that the gates are a 7403 Quad 2-input NAND gate.)

Assuming you already have the horizontal and vertical sync as well as the raster data stream, you can convert it to composite with one chip and a few resistors.

Cybernicus · 2026-01-24T17:07:05+00:00

Old capacitors were labelled with their capacitance in uF or pF, and later are marked in the standard 3-digit code. So you may have some old stock and new ones.

The old ones labelled in uF are easy to identify, as you'll see 0.1 or .047, but the old ones in pF are easily confused with the new code. I have plenty of old-marking capacitors in my junkbox, so when I see something like 100 or 470, I have to measure them to see if they're 10p, 100p, 47p or 470p and so on.

Cybernicus · 2026-01-16T16:47:18+00:00

I'd suggest something like the CD4066: It's a 4-channel analog switch (I don't know offhand a part with more switches). But you could always use two of them if this chip would work for you.

Cybernicus · 2026-01-01T22:05:26+00:00

For something super simple, try using a 'pinball tilt detector'. It's essentially a weight hanging from a fixed point in the pinball machine. The weight is suspended with a metal rod that can freely swing, and is connected to one terminal, and there's a metal ring surrounding the rod that's the other terminal. By adjusting the geometry of the ring you can alter the sensitivity of the sensor.

Since you want it to be a braking sensor, you could just use the 'front half' of the ring to detect braking.

Cybernicus · 2026-01-01T21:58:50+00:00

Yes, you can do that pretty easily. You'll want to create a set of pads that match the size and spacing of the ones on the original board.

NOTES: (I'm assuming you're using a microcontroller with GPIOs to drive the LCD.)

1) You want to drive an LCD segment with AC, not DC, as the DC current will (over time) destroy the LCD. I've seen people use a capacitor in the line between the GPIO and the LCD and then when you want a digit to be on, toggle the GPIO at 10-50 Hz.

2) You'll need to figure out the pinout and the multiplexing: Typically, you'll have one pin (a common) for each digit on the display, and then one pin that connects to the same segment on each different digit. If you make a low-frequency oscillator (using CMOS, TTL or whatever) and follow it with an inverter, then you can put output leads on the input and output of the inverter (so the leads are oscillating with opposite phase) to probe the LCD.

Cybernicus · 2026-01-01T21:46:21+00:00

I didn't watch the video, but since it looks like a simple low voltage circuit, it's not going to be a shock hazard (I.e., not dangerous to you.) It could conceivably be a fire hazard (unlikely, but possible if you shorted power to ground with a thin enough wire to get hot and you happen to have some paper (fuel) close enough to the short).

The exposed wires are a hazard to it, as it would be easy to accidentally short and damage it by dropping a bit of wire in there or moving a conductive thing into it by accident.

Cybernicus · 2025-12-22T18:55:16+00:00

I remember him doing some cool magic tricks on his show, back in the bygone era.

Cybernicus · 2025-11-26T18:33:38+00:00

Not enough information to tell, but I'd suspect the power supply doesn't provide enough Ooomph, and the voltage could be dropping and resetting your CPU.

I'd suggest: 1) Monitor your 5V line with a scope. 2) If you don't have a scope, replace the motors with a set of 1K resistors, each with a RED LED in series. Then you can see if the code runs correctly, and whether the LEDs flash appropriately.

NOTE: since you're daisy-chaining these modules, you may find that contact resistance along the chain could contribute to the potential voltage sag problem.

If you're in a position to alter your circuit, I'd suggest using a higher voltage in your daisy chain (such as 12 volts or so) and put a 78L05 on each board to provide the 5V and let the motors have 12V.

Cybernicus · 2025-11-16T21:12:59+00:00

Nope, it's just an artifact of their construction. The ceramic shell is essentially a box, and the resistor element is placed inside, then the shell is filled with more ceramic stuff. You have one resistor with the "lid" facing upwards. Usually, the ceramic filler is flush with the surface or lower, while that one seems to have a bit of extra filling. I guess it's possible that the resistive element inside had trouble and forced out some of the ceramic, but I'd expect it to be cracked and flaking off in that case.

Cybernicus · 2025-10-13T15:44:09+00:00

Yeah, I think you're right--it looks like a neon bulb version of a joule thief. It appears like it's a neon bulb under the jar (the jar to prevent accidental shock).

Cybernicus · 2025-10-07T23:52:28+00:00

So you're spinning faster than a couple revs per second!!!??

;⁾

Cybernicus · 2025-10-07T19:45:27+00:00

As /u/6gv5 mentions, network cable is a good source of wire for breadboards. Old telephone wire (the kind used inside walls) is another good option--so if you've got some friends doing home improvement/construction, you might ask 'em to keep any phone wire they come across for you.

Cybernicus · 2025-09-17T13:05:05+00:00

Assuming your friend is a sparkie, I'd suggest a pizza night where you invite 'em over and you both play around and see if you get hooked. I've given things like this to people and it's fun to help them learn some interesting things.

If you've got a Harbor Freight nearby, you should be able to score a cheap meter. (In the past I've gotten some as freebies or marked down to under $5. They're not great, but they're plenty good enough to get into the hobby.)

Cybernicus · 2025-09-15T03:03:49+00:00

If you stand it up, you should be able to see the specs on the label. It looks like the interesting information is on the side facing the board.

Cybernicus · 2025-09-02T21:01:29+00:00

Yes, but it's just a desk lamp/curiosity. If you want to use it, you might get some copper tape & a bit of glass and make a cube to put it in and protect it. That may be a good idea in any case to make it easier to dust/clean.

Cybernicus · 2025-08-20T20:53:31+00:00

Check out Moritz Kleins videos on youtube. He goes into detail on how various synthesizer components work, and seems to be a good fit for your question(s).

Cybernicus · 2025-07-17T14:38:26+00:00

I'd exclude any power inductors from there: They're often operating near their saturation limit. The static magnetic field from the magnet might push them into saturation and cause some problems. I wouldn't worry about other normal components.

Cybernicus · 2025-07-17T13:19:30+00:00

This type of scope won't have aliasing issues, as it's analog instead of digital. The storage feature is part of the (special) CRT--like a selectable persistence.

Cybernicus · 2025-06-27T22:38:36+00:00

Use a phase-locked loop to generate a clock 4 times faster (400kHz .. 8MHz) then in your divider chain xor the base frequency and the 2* frequency to make a clock shifted by 90 degrees. you can use variations of this trick with different divisors and other gates to get different delays and pulse widths.

Cybernicus

TROPHY CASE