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Why 2 transformers? (pic)
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ArthurDent:
One problem with the analysis of this supply is thinking of it as a standard power supply to regulate the output. It functions as a variable power supply from about 8-12VDC and the output voltage to the peltier cooling device is controlled by the NTC sensor signal that goes through IC2 to IC1 that controls TR1. Watch the video and look at the two LEDs on the schematic. When the sensor is calling for heat both LEDs are on but when it gets to the set point the output drops to as low as about 8 volts and the green LED, that has a 7.5 volt zener in series with it, goes out.

Once you start looking at this as a temperature controller rather than a standard SMPS it makes more sense.
schmitt trigger:

--- Quote from: Shock on January 14, 2019, 10:47:29 am ---Seen this video at all? Always pays to dive into google and lookup on the model and board part numbers. Especially consumer gear it's probably been fixed a hundred times already.


--- End quote ---

Absolutely correct.
These types of supplies are very cheaply mass-produced by one of the larger far-east suppliers (Delta, LiteOn, and such) and are found literally everywhere.
billbyrd1945:
Watched it many times. I don't have enough experience to make much sense of it. I'll try again. I may not have the aptitude for electronics. But thanks for all the help.
ArthurDent:
Thinking of the controller board as just a SMPS isn’t the way to understand the whole wine cooler. Instead of the board being a SMPS that senses the output voltage and feeds back a sample of this voltage to an IC that keeps the output voltage constant, it has a temperature sensor that feeds back a sample of the temperature (as a voltage) to an IC that varies the pulsed output voltage from about 8-12 volts to keep the cooler temperature constant.

If the wine cooler is working you should eventually see the controller’s red and green LED flash slowly as the peltier effect cooler is fed power to cool the inside of the wine cooler. If the LEDs flash rapidly, just one LED is on, or both are out, there is a problem somewhere. I believe a common failure mode of any cooling device like this is the bank of thermocouples that make up the peltier effect cooler that are fed the D.C. power at a few amps starts getting weaker and the cooling gets less and less effective as the cooling unit draws less and less current.

You haven’t said what the problem is and why you have been working on the wine cooler for a few months. Is it dead or is it just not cooling properly? If it isn’t cooling properly then if you monitor the D.C. voltage across the fairly heavy wires going to the cooling unit when you first power it up you should see the 12 to12.5 volts that it shows on the schematic.

If everything is working, after some time the temperature should start to drop and eventually reach the set point. If you have 12 volts and it isn’t cooling as it should then it is probably the peltier effect device. One way to check the cooler is to disconnect it from the controller board and connect it to a D.C. bench supply. Increase the output voltage to 12 volts and see if the current drawn increases to 4 or 5 amps. If it does and the unit cools down, the cooler is o.k.. If it draws less than 4-5 amps at 12 volts then the peltier effect device probably has some open cells and needs to be replaced. There are inexpensive replacements on eBay and plenty of videos that show how to replace the cooler and it isn't that hard.
billbyrd1945:
Your response is what I've been needing because it addresses the problem as a system. Unfortunately, a precise sequence of events may not be possible as I have poked around so much without keeping adequate notes. But, it
all started one day when my wife reported a strange noise from the kitchen. I found the noise to be coming from the
wine cooler door display which was flashing rapidly. I was at least smart enough not to order a new door. It proved to work normally when I connected it to a known power source.

Then I took off the back panel and found twin power supplies connected to a common break out board. The voltage for the door emanates from the BOB, so I decided the problem had to be related to it. There's only on IC on the BOB, and my thinking was that it was far more likely to be the culprit than one of the caps, resistors, diodes, etc.
I found the IC on ebay and waited several weeks. I installed it. No change. Then I started deep research into common failures of switch mode power supplies. That led to my replacing caps, then diodes, then transistors.

I had violated all the rules of trouble shooting by replacing rather than testing. That's not the way I've spent my life as a person who generally succeeds in fixing most anything around the house. But I was out of my element. I simply didn't have any way of testing, didn't know how.

So, I began asking one by one about this component and then that one. The idea was to learn how to test each component and then order parts based on those tests. I mostly got no help so resorted to replacement as a process of elimination.

(At this point the only things I haven't replaced (on the two PSUs and the BOB) are four zener diodes, two for each PS. They are ordered.)

After each attempt at repairing the boards, I'd hook it all up to find that it still wasn't right. The last attempt had the fans for one Peltier spinning slower that what I would expect while the other set of fans would pulse off and on. I could hear the faint sound of switching from both power supplies. I only just now learned that the switching sound comes from the power transistors.

I did test both Peltiers with a 12v battery charger and both would heat/cool in a way that would seem normal based on what I understand about them.

And that, sir, is my story. I hope I haven't left out anything important. With regard to finding success stories that I could benefit from-- not so much. I've found a few old posts about dealing with failed units, but the posters usually lose interest in the subject once they've found their problem (or have given up on it).

As previously stated-- it ain't about the money. I've already spent more than the cooler cost. I'm just obsessed with seeing it through. After that I'm going to find myself a good electronics project with documentation so that I can go from start to finish without having to work blind.
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