I've been trying to enter the electronics repair scene with this old mini fridge I found a while back. When plugged in (not on) it emits a very quiet intermittent squeak that devolves into a constant whine, which persists after unplugging. When turned on, it is a much louder high-pitched constant whine. (Fan does no move at all.) After searching the internet, general consensus was to replace capacitor C8 (which for me is a 10uF50V), which I did. While I did so, however, I think I shorted what I think is the inductor trying to discharge it, and wonder if that may be a new issue. It used to to make intermittent squeaks when turned on, it is now one long drone. I'm now scared to touch my multimeter to anything (previously made sparks) and the general fix given by the internet has failed (likely due to my own actions). If I'm missing anything crucial, please ask; this is my first post on the forum and I may be doing something egregious I'm unaware of. Thank you!

P.S. Board looks different from all the pictures I've seen online as well. Not sure why. Worried to replace with a different board.

 

Welcome to AAC!

The reference to C8 is for a different board and does not apply to your board which is an HYS48-12/110 power supply.
This is one we have not seen before on AAC.

Looks like it is time for a replacement PSU.

 

...I'm afraid I don't know what that means. I would have thought the PSU was the cord...which I suppose isn't out of the question. I'm using a 7A 125V cord, but I don't know if that's correct, I just found it and it happened to fit

 

PSU stands for Power Supply Unit which is the entire board.

 

So...it's shot? Not worth fixing?

 

So...it's shot? Not worth fixing?

I didn't say that. Of course it is worth fixing if you know what component(s) need replacing. In order to do that it helps if you can find the circuit schematics.

 

I thought that might be what you meant by replacement PSU. I don't think I'll be able to find a circuit diagram, even the board itself is hard to come by. How should I go about safely testing each component to see if it works?

 

I thought that might be what you meant by replacement PSU. I don't think I'll be able to find a circuit diagram, even the board itself is hard to come by. How should I go about safely testing each component to see if it works?

One way to do that is to remove each and every component and test each one separately. That is not something I would want to do. It is more cost effective to buy a replacement power supply unit.

 

I did what I could with a cheap multimeter. Capacitors have high resistance, inductors have low, resistors aren't open. I noticed when it's plugged in, the output says 12V (like it's supposed to) but the moment I turn it on that drops between 2-3. Any idea why that would be?

 

You can buy a 12 V / 5 A PSU for under $10.

 

I'm a bit wary of that, from another thread I read to solve this issue: "DO NOT put in a regular 12V power supply! It won't not have the thermal regulation or safety features of the original control board, which is bad because the inside of the fridge can get very hot."
Hence why I am hesitant. Secondly, the fridge isn't that high of a priority. I want to learn the process of isolating, diagnosing, and fixing a problem, so I can work on larger (and more expensive) products where just replacing the board is not as useful.
Anyway, in that time and took out and tested the two green 1000uF and the big black 100uF capacitor on a more expensive multimeter. The 100 came out to ~90uF, but the greens were 30 and 300 uF respectively. Is there any other confounding variables that might be causing that (too much or little charge?) or am I good to replace those and see if that helps?

 

Here is some advice. This is a non-isolated switching PSU. The reason I have lived for so many years up to now is because I stay away from these kinds of circuits. They are lethal.

 

First of all, two green capacitors look suspicious. Their tops appear swollen.
Despite their measured capacity, they may be bad due to increased ESR .
For testing, you can simply solder an additional capacitor in parallel to existing. 1000uF 35V or so

 

First of all, two green capacitors look suspicious. Their tops appear swollen.
Despite their measured capacity, they may be bad due to increased ESR .
For testing, you can simply solder an additional capacitor in parallel to existing. 1000uF 35V or so

I agree, C10 seems to have a slightly bulging top, hard to say but do check every similar capacitor, they should have a perfectly flat top, if its bulging even slightly, then replace, that might be all that's wrong, its common too.

I've seen systems stop working when a 100uF value dropped to 85uF, some circuits are quite sensitive to the change in value as a capacitor ages.

 

While you are at it, there are two 3-pin semiconductor devices mounted on heat sinks. See if you can read the markings on these two devices.

 

Thank you, Pyrex and Futurist, you guys are spot on.
I have since fixed the device (don't know how to make this a "success story") and that was the exact issue. After taking the caps off the board and measuring them, the green had a nominal value of 1000uF and measured much below that. I replaced those two the next day and the fridge worked as intended.

 

Now that I looked at the photo that was taken at an angle I can see it now.
One green capacitor has a slight bulge on the top. The other is showing a spot of brown crud at the center of the Y.
Whenever you see signs of brown crud coming out of the top of a capacitor that is a sure sign that it is passed it's best use date.

 

Thank you, Pyrex and Futurist, you guys are spot on.
I have since fixed the device (don't know how to make this a "success story") and that was the exact issue. After taking the caps off the board and measuring them, the green had a nominal value of 1000uF and measured much below that. I replaced those two the next day and the fridge worked as intended.

I had a home built PC many years ago (like 2005) which had been fine for several years, then it began to just reboot once or twice a day. Then it started to refuse to start when I pressed power on, would take three or four attempts.

Turns out it was exactly this issue (once I heard of this plague, I looked and saw bulging on a mobo cap, so it was a no brainer), I've never forgotten this. I'm sure a lot of older folks here remember this, I'm not a professional engineer so I'm sure pros were well aware.

https://en.wikipedia.org/wiki/Capacitor_plague

I mean, looks familiar?