Wine Fridge Power Board

[keeney123]

Re: Wine Fridge Power Board

Also, acronish I would look for a short on anything that is connected to the R35 2 ohm resistor like the T7 mosfet. Those marks on the back of the board are definitely cuts with X-acto knife. I would ohm out from that heat sink to the rest of the circuit to make sure it is still connected.

[keeney123]

Re: Wine Fridge Power Board

The SCH can be drawn by hand from what I have marked on the board, I use ALTIUM DESINGNER and Solidworks at work.

It is just difficult for a person like me with dyslexia I can get through it alright it just take me about 5 times longer than an ordinary person.

[budm]

Re: Wine Fridge Power Board

That traces were cut since the heatsink is at hot potential and due to no insulator sheet is not used to isolate the TAB of the MOSFET from the heatsink.
I did not draw up the diagram for now because we just want to locate bad parts for now.

[keeney123]

Re: Wine Fridge Power Board

That traces were cut since the heatsink is at hot potential and due to no insulator sheet is not used to isolate the TAB of the MOSFET from the heatsink.
I did not draw up the diagram for now because we just want to locate bad parts for now.

If you look on the top of the board on T7 you will notice that the mosfet has a heat sink pad and the screw has an insulator that goes through the hole in the tab.

[budm]

Re: Wine Fridge Power Board

I would measure and verify that there is no electrical connection between the tab and the heatsink in case it was not properly installed so some one cut the traces.

[keeney123]

Re: Wine Fridge Power Board

Yes, acornish it would be a good idea to ohm out from the heat sink to the tab on T7 to make sure there is no short, as budm suggest.

[acornish]

Re: Wine Fridge Power Board

So, the fun continues. After replacing the two 13005 transistors on the board, checking the caps and replacing the resistors, I plugged it in and almost immediately it shorted/arced in the back of the board (see photo-I have included photos of both sides of the board).

It was mounted back into the fridge but WAS NOT in contact with the fridge itself-so that wasn't it. Of course, this blew the fuse and the 13005 transistors, which I have once again replaced, but now it is really dead when I try to power it up. The Caps still look OK no bulging or leaking. The diodes on the primary side of the board are still OK and the resistors appear fine and have not burned out, the transformer also appears fine.

Things on the secondary side look OK, although the MOSFET there (I think its a MOSFET), #STP52045C may be cooked. I have a transistor tester on the way to be sure.

Anyway, the arcing happened near the area where someone in the past isolated (or tried) to the heat sinks for the two 13005 transistors. Could that arching have been caused by this, either because it was incomplete or because it was done in the first place. That is, should I "repair" the etching done to isolate the heatsinks? In thinking about it, I don't think it should matter, but being a rookie, I might be missing something important.

Again, thanks for the help. A

[kc8adu]

Re: Wine Fridge Power Board

those transistors need the mica/silicon rubber insulators and plastic washers.
mica types need compound too.
the upper one is missing the washer.

[acornish]

Re: Wine Fridge Power Board

kc8adu,

OK, I have added a rubber insulator, however the tab of the transformer is still electrically connected to the heat sink. Referring to my image of the back of the board, the lower transistor's collector is connected to the heat sink. This is not the case with the upper transistor, which is isolated due to the "scratches" put in the board. Again, these were there when the unit came to me.

Could the lack of connection between the heat sink and the emitter on the upper transistor be part of the problem?

Secondly, when the unit arced, could that have fried something on the secondary side that I should be checking?

Thanks again-

[acornish]

Re: Wine Fridge Power Board

oops, my question in the second paragraph should have read:

"Could the lack of connection between the heat sink and the COLLECTOR on the upper transistor be part of the problem". I typed emitter by mistake.

[keeney123]

Re: Wine Fridge Power Board

oops, my question in the second paragraph should have read:

"Could the lack of connection between the heat sink and the COLLECTOR on the upper transistor be part of the problem". I typed emitter by mistake.

I would not think that this would cause a short on your board, but it will not hurt to reconnect it and again make sure that the heat sink on that transistor does not electrically connect to the tab. The other transistors tab is electrically connected on the bottom of the board with a land so I would think this transistor does not need the pad and the insulated insert that goes through the hole in the tab that the screw goes through. Instead of just replacing parts you will need to find out what is shorted as I have already stated.

[acornish]

Re: Wine Fridge Power Board

Thanks again-I had wondered about that second transistor as it did appear connected to the board. I will continue looking for the short.

[acornish]

Re: Wine Fridge Power Board

So, I am back at this again after a bit of a break. The good news is that the board now works. The fans turn as they should and everything is behaving itself. The board puts out about 5.5 to 6 V when measured at the point where the peltier unit connects.

However, the "bad" news. When I connect the peltier unit, the fans stop and the output voltage drops to about 1.6 V.

I know that the peltier works as I have tested it with an independent 5 V power supply and it gets very warm and very cold as it should.

I have tired disconnecting the wires from the temperature sensor in the fridge and the LED light in the fridge, but this does not affect anything. Voltage is fine with no peltier unit, but drops when the unit is connect. I should mention that I have test the board with several "good" peltier units and it consistently acts this way.

Anyway, any thoughts or suggestions as to why the power board "throttles" down when the load is connected to it.

Thanks again Anthony

[keeney123]

Re: Wine Fridge Power Board

I am thinking the Peltiers should be getting 12 Volts DC? Same with the fans. See if you can see a voltage rating on the fans.

[acornish]

Re: Wine Fridge Power Board

Keeney123, yes you are correct, both the fans and the Peltier are rated for 12v DC. Any idea why the board's out put is so low? At best I will see 6v, but with the Peltier attached this drops to less than 2.

Thanks again A

[keeney123]

Re: Wine Fridge Power Board

So what did you do to get rid of the short? This is where I would start. If you replaced something to allow the board to work you may have not gotten all of the problem. I would make sure the transistors are both good. I think BudM supplied you with the from end of the circuit. Now it maybe a good idea to develop a schematic so we can look at exactly which components are doing what. I know the basic concept of what is happening but my memory of exactly what is happening is vague. Basically you need the AC to be rectified to DC. This DC is then pulse width modulated and then the thermal couple along with rheostat that controls the inside temperature are used to create a duty cycle of the pulsating DC. Near the end of the circuitry just before the DC is connected to the fan and Peltier there is a transformer that charges up and then is turned off creating a collapsing voltage in the reverse direction. This Transformer is called a switching transformer. So anything along this line could be bad to create a faulty circuit. So if you check out the front or the power section of the circuit. The diodes, transistor, Capacitors, IC power voltage and can not find a problem with them then a Schematic will be needed. This will give a whole functioning view of the circuit. At this time one will break down the circuit and test the various part. Some of this can be done with just a multimeter, but to be able to look at the signals one needs a Oscilloscope to verify they are correct and have a correct timing.

[acornish]

Re: Wine Fridge Power Board

keeney123

Thanks. WRT to the short, it was rather my fault. When I replaced the transistors I used a conductive thermo-compound (a stupid rookie mistake). To get the board to "work" I re-replaced the transistors (all of them) as well as a number of diodes and resistors that were faulty. I picked up a specific transistor/diode tester to check these out and replaced the "burnt" one with identical parts. As well, I used a NON-conductive thermo-compound when I put it all back together, so no fireworks. It does sound like I have somehow managed to reduce the board's output by half as it should be able to generate 12 VDC (it is a Hanny HYS60-12-KD board).

I will see what I can come up with for a schematic and post it when I can. With respect to an Oscilloscope, I do have one, but can't say that I am proficient with using it. I have mentioned in the past that I deal with a lot of "surplus" equipment and someone was getting rid of a Hitachi V-212 20 mHz 'scope, so I "recovered" it. I am still in the processes of learning how to use it. If I knew where to connect it to the board, it might provide some useful information.

Could I somehow have damaged the switching transformer(s) (there appear to be two) when things shorted out?

Thanks again for the help-A

[keeney123]

Re: Wine Fridge Power Board

Yes a schematic would help at this point. I am going to be very busy for about a week. I am repainting my apartment as I am trying to move back to MA where all of my family lives. If you could look at the front circuit or power circuit using BudM component layout to verify the AC is being turned into the DC at the correct voltage. With a scope the AC power circuit one would connect ground of scope to ground of input power. In the IC you can look up the part number and there should be a pin out of the IC. It will have a Ground and a VCC. Once you know where the Ground of the IC is then you can ohm out the ground to a more convenient place to connect the ground of the scope. If you are unfamiliar with a scope it is best to use the Multi-meter until someone can walk you through the steps of the scope.

[acornish]

Re: Wine Fridge Power Board

Thanks Kenney123, I will do that and post the results when I can. Good luck with the repainting and the move. I hope all goes well for you and thank you again for your insightful help.

[acornish]

Re: Wine Fridge Power Board

I would double-check the polarity and value of the new caps, and their soldering. Then I would confirm the cables/connectors didn't get mixed up. A felt pen mark or two helps.
220V primary caps are OK. It wouldn't give troubles you are seeing.

I found a schematic for a wine-cooler power board that looks similar to what you might have, except that extra socketed-DIP IC. I can't read PCB part #'s in your pics.
That circuit shows it's an always-on 12VDC 5A power supply and a thermistor/op-amp with power transistor (somewhere) linear? controlling the fans and Peltiers, which are all in parallel.
The temperature sensor on CN1 has something in series on CN2 which I think is a door switch.

You can try warming up the temp sensor with your fingers or a lighter and the voltage to the Peltiers/fan should ramp up. Or apply ice and it should back off.
Can you check the 12VDC is always good, LEDS not flickering etc.

Redwire, I have been working a similar issue with a Hanny board that you refer to above.

Currently I have my board working, but the minute that I attach a Peltier to it, my output voltage drops from about 8.5 VDC to around 1.5 V.

I am still scratching my head trying to figure this out, and 123kenny have been helping, but I am wondering if you have higher resolution versions of the schematics that you post here? They might help me figure out what should be happening.

Thanks-acornish