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Ignorant questions about fan controller for refrigerator

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fastline

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Wife's small refridgerator stopped working. I tore it down just for fun. Found that these little guys do not even have a compressor. they just use heat exchange somehow with some heat sinks and fans. Anyway, I plugged it in and found that the control board was squealing like a pig. The fans would rotate about 5* every second and stop. Kind of like it kept resetting or protecting itself. You could hear the squeal stop about every second.

I removed all loads to the board and it just has a constant squeal. I think all the fans are 12V DC. I seem to remember you experienced techs mentioning that a squeal points real hard to a certain component?? I do not have any visible damage on the board and there is a 3A fuse in it that is not blown so I a little puzzled. Could this be a mosfet or does this point to too much ripple getting over to the DC buss? Just curious. I am sure someone smarter than me could trouble shoot this one in 5 min.

I checked for shorts on the twin mosfets on a heat sink and gate to drain did not show shorted but I realize that does not mean all good..
 
Sounds like the refridgerator uses thermo-electric "peltier" device, pretty common these days. As far as the controller squeeling, hell if I know. ( could it be arching ? )
 
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It's an smps power supply that puts out 12 v, ~6amps. The output cap is most probably toast which causes to much ripple and the inverter go into max mode to try and keep up the effective voltage. If you keep letting it squeal the mosfets and fuse will go out.

There are also 2 ohm 1/4 watt resistors feeding the mosfets that go out as well.
 
You sound like you know this circuit. I have personally never seen a cap fail without some visual sign but how common is that? I don't know how many times I have removed caps on a whim only to learn that they are fine.

Also, you say "output caps", are you referring to the main power supply caps or the small caps in parallel with the output to the load?
 
You sound like you know this circuit.
Well, I have worked on similar type fridges. Weather it's the identical circuit is something else. Thinking back, I believe it used tranistors, F13005.

I have personally never seen a cap fail without some visual sign but how common is that?
Lucky you. It depends on the cap and manufacturer.

I don't know how many times I have removed caps on a whim only to learn that they are fine.
If your removing caps on a whim to test them then you do not have an ESR meter. Without An ESR meter you cannot properly check the caps 'quality'.
An ESR meter is the way to go. You can have a cap read proper uF with a basic cap meter but be defective by having a high internal resistance. An ESR meter does this and most times can be used with caps in circuit. Like everything it depends on circuit design.

If'n you do not have one , use a scope on the cap and look for ripple. If'n you don't have a scope, use a DVM on DC and AC volts. Have you measured this?

If the cap is failing, it will need to be replaced with a Low ESR type 105'C cap of equal quality. Regular joe blow cap will not work.. for long, if at all.

Also, you say "output caps", are you referring to the main power supply caps or the small caps in parallel with the output to the load?
Output caps are at the output :D. Around 1000 uF around 16 to 25 volts.

Start by measuring the output and determining the manufacturer and series of the cap/s at the output. A nice pic of the boardwould help.
Cheers
 
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Ask and you shall receive. You can see where I already removed the filter caps on a whim because it looked like they might be leaking. After inspection and a few tests, I think they are still good but I REALLY need an ESR meter like now... That gunk on the board is unknown at the moment. Looking at the bottom of the caps, there is no clear indication of leakage. They are holding 1.5 right now with no problem and test OL continuity across them

My scope is from the 70s. We are shopping for a real one right now but trying to get something that will also calculate power quality in main service power.

Anyway, you can see the line of output plugs on the right, each is pretty much just a fan. There was one fan that was a little stiff so not sure if that over worked the circuit or not.

The two caps near the outputs are 2200uf/16v and 220uf/16V. No visual issues BUT....... I am looking for an ESR meter right now.....lol

Let me know your thoughts.
 

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Ok so Your board is definitely different than the ones I've played with here.
Put the filter caps back in, watch polarity, and measure the output voltage Ac and Dc with and without a load. Try not to leave it on too long so as to not make things worse

In addition to my previous post questions, what are the marking on the output to220 devices on the large heatsink?

ADDED what do you mean by
"They are holding 1.5 right now"
 
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To-220s look like STPS2045CT. Might be a little off on that. SCHOTTKY DIODES

J13007-1, F, and J09 are on the other 2 TO-220s that in singles. Not yet sure what those are either... HIGH SPEED TRANSISTORS
 
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I was advised to add a detail on the issue of this fridge. Turned out to just be some failed caps. Circuit was whining with no load. After caps were replaced, the circuit was dead silent and has been running for 12 hrs straight without issue.
 

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fastline said: "That gunk on the board is unknown at the moment."

FYI -- It is not at all uncommon for a manufacturer to use mastic or "hot glue" when installing certain larger devices, specifically caps and coils. The purpose is to quiet the unit by dampening or absorbing vibration of the component as well as to physically support the component in place. Also - you will often see the mastic on fuses - particularly when the fuse is installed in a holder. If the mastic is broken or removed, the manufacturer (or repair tech) will know that the fuse has at least been out, and was probably changed...
 
I was advised to add a detail on the issue of this fridge. Turned out to just be some failed caps. Circuit was whining with no load. After caps were replaced, the circuit was dead silent and has been running for 12 hrs straight without issue.

fastline, good job. Put a post with the Model # in the posts header (Solved) Then put the pic in again with the fix. Caps are mentioned in the post with the values.

It will help the web crawlers locate for someone else who may need or want your findings.

I'm glad you got it. :)
 
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I was advised to add a detail on the issue of this fridge. Turned out to just be some failed caps. Circuit was whining with no load. After caps were replaced, the circuit was dead silent and has been running for 12 hrs straight without issue.

Most likely they failed because of high temperature above or near their max temp allowance. Either that or they are just a cheapo brand. In the picture I can see those faulty caps are right next to a big resistor that is very discolored.

-Ben
 
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