Wine Fridge Power Board

[dunkel]

Re: Wine Fridge Power Board

I think that there may be errors in the hand drawn circuit diagram, but ISTM that there is enough symmetry in the circuit to enable the values of some of the damaged components to be inferred from other components.

R35 = R38
R34 = R37
D10 = D12

Thank you so much, now i just need to find out the value of the D12 diode which i have in good conditions.

do you know a replacement for the transistors 13005D ? T6, T7? can I use the MJE13007 ?

Thanks!

[keeney123]

Re: Wine Fridge Power Board

The Peltiers are a big problem with these cooler. First the Chinese ones one can connect a ATX 12 volt power supply directly to them and without putting them in the unit they will draw maximum amperage. The Manufacturer claims they are capable of drawing 6.5 amps at 12 volts DC. My measuring them for current outside of the heat sink the maximum they will draw if 2.6 amps. If you let them continue to draw that current they will burn out. I have tested them. Actually if you look at there graph you will see they are only capable of drawing about 4.5 amps at 12 volts. As the surface become the same temperature on each side the draw of current becomes less until they equal practically 0 Amps. The Black & Decker unit I tried to repair was not even listed on the B&D site and I read that they did not even support repairing their thermo-electric frig. I though perhaps the US supplier would have better quality Peltiers and I guess they do as one person bought these and was able to obtain 6.5 Amps of current out of them and they actually had a high heat output until something happen and they no longer drew out heat. Of course 6.5 amps was a lot and perhaps they could not hold up to that. The other problem is cost of them. The Chinese sell them for about $3 a piece, but they do not work. The US sells them for minimum $21 each which prohibits buying them as $42 dollar investment in a cooler one can by used for $60. The problem is not so much testing the power supply and temperature control as it is can these two Peltier actually cool 1.5 cubic foot of air from 70 F down to 37 F. and if the ambient is greater than 70F are the Peltiers incapable of overcoming that temp. These numbers are in the specifications of the frig. I was working on and 70F to 37F were maximum ratings. They also say that it will take at least 10 hours to do this. They also say if you open the door frequently, more than one time a hour, the inside will heat up again and will take time to re-cool again. This is the problem. Perhaps if one were only cooling off enough area just for a sandwich and coke that might work. One would have to figure out how many BTUs each Peltier is really capable of cooling.

[fzabkar]

Re: Wine Fridge Power Board

If I were testing this PCB on the bench, I would replace the Peltier cooler with a 12V dummy load. I would also lift the two diodes that feed pin #1 of the TL494 from IC2 and IC3. This will allow the supply to reach its full design voltage. Let's call this voltage Vp.

I would then reconnect the diode from IC2 and substitute a dummy resistor for the NTC/rheostat. Typical thermistors will have a resistance of 10K or 5K at 25degC, and a much higher resistance at 0degC. I would then vary the resistance between these two settings (or -10C to +40C) while observing the Peltier output voltage. The voltage should be less than or equal to Vp, never greater. I expect that the voltage should fall as the temperature falls.

Next I would examine the effect of ambient temperature by reconnecting IC3 and heating or cooling the TO92 device (with spray freeze or a hair dryer). Do this with the NTC set at 25degC. As before, the voltage should be less than or equal to Vp, never greater.

[keeney123]

Re: Wine Fridge Power Board

AFAICT, the offboard temperature sensor (the one inside the fridge) is an NTC thermistor, not a thermocouple. Its resistance, together with the rheostat, forms the bottom end of a potential divider. As the fridge becomes colder, the non-inverting input of the opamp rises, causing the opamp's output to increase. This then causes the Peltier's supply voltage to fall.

The TO92 packaged device adjacent to IC3 appears to be a second temperature sensor. I believe it senses the ambient room temperature. I would very much like to see its markings, but for some reason it has been removed from the PCB.

I was just going by the one I was repairing frig. about 6 months ago. They all must be a little different.The problem I had was the Peltiers could not withstand more than 2.4 amps of current at 12 volts DC. I bought them from China. Another person had the wine cooler, in a earlier post he bought American Peltiers that were driving at 6.5 Amps of current at 12 volts and they were removing the heat, but then something happen and they stop getting hot and never cool much down below 68 f. I guess he gave up. I think what happen is the Peltiers failed. I have yet to see one of these things really work. Those Peltiers are rather small to remove 1.5 cubic feet of heat. I believe the power supplies are big enough to drive them.

[fzabkar]

Re: Wine Fridge Power Board

AFAICT, the offboard temperature sensor (the one inside the fridge) is an NTC thermistor, not a thermocouple. Its resistance, together with the rheostat, forms the bottom end of a potential divider. As the fridge becomes colder, the non-inverting input of the opamp rises, causing the opamp's output to increase. This then causes the Peltier's supply voltage to fall.

The TO92 packaged device adjacent to IC3 appears to be a second temperature sensor. I believe it senses the ambient room temperature. I would very much like to see its markings, but for some reason it has been removed from the PCB.

[keeney123]

Re: Wine Fridge Power Board

The temperature sensor is a thermo-couple and a rheostat controls how cold it gets. I think the thermo-couple is a K type but am not sure. One of the IC s should control the duty cycle of the PWM supply. That way as the frig. gets colder the duty cycle decreases as it approaches the temp that was set. Also, there maybe a LED inside the frig. that stays on all the time. It is just used as a light.

[fzabkar]

Re: Wine Fridge Power Board

I realise it probably won't be of any help in solving the immdiate problem, but I've drawn the area of the circuit that controls the TL494 regulator. ISTM that the regulator gets feedback from the Peltier output, the NTC sensor (via IC2), its own internal 5V reference voltage (?), and IC3 (uC). IC3 is a microcontroller whose function appears to be to monitor the ambient temperature, but I could be wrong about this.

            ___
  Vcc (TL494-12) <---|___|--+---+
               |  |
               |+ |
               === |
               --- |
               |  |    C
     5Vref   5Vref   === |   ||
      +     +    GND | +--||---+
      |     |      | | ||  |
     .-.    .-.  +------)--| ___ |---+
     | |    | |  |   | +-|___|-+  |
     | |    | |  |   |   R    |
     '-'    '-'  |   |8       |
      |     |   |  2|\|       |
  +-------+----+  +-----+----|-\ 1      | ___  D
  |    |  |  |    IC2| >-------------+-|___|-->|--> TL494-1
 +| NTC .-.  |  .-.  +----|+/ LM358
 ===   | |  |  | |  |  3|/|4
 --- +->| |  |  | |  |   |
  |  | '-'  |  '-'  |   |
  |  +---|  |  |   |   ===
 ===   ===  |  ===  |   GND
 GND   GND  |  GND  |
        |     |
        +----------+

            .-------------------------.
            |             |
        +------|1           14 |-- NC
        |   |      IC3      |
        | o---|2 NC?        13 |-- NC
        |   |      uC      |
        | o---|3 NC?        12 |-- NC
        |   |             |
   5Vref <----+------|4 VCC        11 |------+
            |             |   |
       ||    |             |   ===
     +--||---+----|5 OSC1         |   GND
     | ||  |  |             |
     |   _-_  |             |
  +-----+ X1 |___| |             |
  |   |    -  |           10 |-- NC
  |   | ||  |  |             |
  ===  +--||---+----|6 OSC2        9 |-- NC
  GND    ||    |             |
         +----|7 ADC in?  DAC out? 8 |--->|----> TL494-1
         |  |             |   D
         |  '-------------------------'
         |
     Link  o
     under  |   |---------|  TO92
     IC3?  o   | o o o |
         |   \ | | | /  Temperature
         |   -|--|--|-   Sensor ?
         |    | | |
         |    | | +--------------------> 5Vref
         |    | | |
         |    | | .-.
         |    | | | |
         +-------+ | | |
             | | '-'
             | | |
           +---+ +--+
           |  |   |
           | .-.  .-.
           --- | |  | |
           --- | |  | |
           | '-'  '-'
           |  |   |
           +---+-----+
             |
             ===
             GND

 +------------+
 |      |
 |      ---            D
 |      ---         +------>|---+-----> Fans / LEDs
 |      |          |      |+
 |      |         .-.     ===
 |      .-.         | |     ---
 |      | |         | |     |
 |      | |         '-'     ===
 |      '-' D1a   L1   |     GND
 |      |       ___  |
 |   -. ,--+---->|--+----UUU---+------+--o  Peltier +
 |    )|(      |     |   |
 |    )|(      |     |+   |     ___  ___
 |  TR2 )|(-----------)-----+  ===   +--------|___|--|___|--+--+
 |    )|(      |   |  ---              | |
 |    )|(      |   |  |               | .-.
 |   -' '--+---->|--+   +----+---------o  Peltier -    | | |
 |      |    |     |               | | |
 +------------| D1b  |     ===              | '-'
            |     GND              | |
            |                    | ===
            |            +----------------+ GND
           D |            |
            V  .----------.    |
            -  | TL494  |    |  D
            |  |     |    +----|<--- IC3 (uC)
            +---|Vcc    |    |
             12|     |    |
              |    /| |1    |  D
              |   / |-|--------+----|<--- IC2 (LM358)
              |  -< E| |    |
              |   \ |-|--+   |
             13|    \| |2 |   |
      5Vref <----+----|5Vref   | |   |  +----- 5Vref
           |  |     | |   |  |
           .-.  '----------' |   | .-.
           | |         |   - | |
           | |         |   ^ | |
           '-'         |  D | '-'
           |         |   |  |
           +------------------+   +---+
           |              |
           .-.             .-.
           | |             | |
           | |             | |
           '-'             '-'
           |              |
           ===             ===
           GND             GND

(created by AACircuit v1.28.7 beta 02/28/13 www.tech-chat.de)

[keeney123]

Re: Wine Fridge Power Board

I think the main power supply is OK, it is the switching circuit that is not working.

I still think those diodes and capacitors are in backwards. That is C13, D10, C14 and D12.

[budm]

Re: Wine Fridge Power Board

I think the main power supply is OK, it is the switching circuit that is not working.

[keeney123]

Re: Wine Fridge Power Board

I wish I have the board in front of me, at first thought I was thinking it is set up as the Voltage Doubler circuit for 120AC line but looking at the connections it does not look right.
So the diode (the one connected to the two main filter cap +/- connection) as shown in the drawing is actually a jumper wire? It has to be for it to be Voltage Doubler circuit.
https://en.wikipedia.org/wiki/Rectif..._rectifier.svg

So here is the update primary side per your recommendations

[budm]

Re: Wine Fridge Power Board

I wish I have the board in front of me, at first thought I was thinking it is set up as the Voltage Doubler circuit for 120AC line but looking at the connections it does not look right.
So the diode (the one connected to the two main filter cap +/- connection) as shown in the drawing is actually a jumper wire? It has to be for it to be Voltage Doubler circuit.
https://en.wikipedia.org/wiki/Rectif..._rectifier.svg

[keeney123]

Re: Wine Fridge Power Board

fzabkar I have corrected it here. When BudM told me that I did not understand as he drew it to DC primary ground and indeed from the picture of the board it actually seems to go to the DC primary ground.

Also remember you are looking at 1/2 of the circuit. So there is feed back to control duty cycle and to turn off the devices it is controlling. These diodes and caps I believe are used for oscillation for the pulsated DC supply.

[fzabkar]

Re: Wine Fridge Power Board

I don't know the reason for the Dxx circuit reference, but, as budm explains in post #104, it "is connected between incoming AC L and another end goes to the junction of those two filter cap not to the primary DC negative as I have drawn". This means that "it appears to be a wire link that programs the fridge for 120VAC operation", as I explained in post #110.

As for the polarities of D10/C13 and D14/C14, I'm still trying to get my head around it. ISTM that the diodes may be reversed, but I'm not certain.

[keeney123]

Re: Wine Fridge Power Board

Fzabkar I do not mind the knit picking that is how something is proving. If you look at previous posts this board was from a unit not working correctly. It was the same as the board that was set up. My belief was that the D10 and C13 of this bad board are in backwards as are D14 and C14 and that is why it did not work. The person that has this board never got back to me. Perhaps the dunkel can confirm the direction of these components. The layout was from a virtual program from BudM all I did was develop a schematic from it. Do you have a schematic of this board or have you repaired these board? Also D14 is there, but it was listed as a resistor by BudM. I just put D14 because it had a marking of Dxx. Which I did not know what that meant perhaps you understand that marking?

[fzabkar]

Re: Wine Fridge Power Board

My eyesight isn't young anymore, and I don't mean to nitpick an excellent body of work, but ISTM that, on the basis of symmetry alone, the network consisting of D10, R34, C13 and the associated transformer winding should terminate at the source of T7 rather than B-. Also the "DIODE" in parallel with D14 is clearly in error.

Edit: maybe R36 = R39

[keeney123]

Re: Wine Fridge Power Board

Yes dunkel the values possible could be in error as the color coding could be different from looking at a picture as apposed to seeing in real life. I Believe the schematic drawing to be very accurate. This can be confirmed by ohming out the various points on the board. As fzabkar said there is a symmetry of the circuit so some of the components are the same because you have two circuit performing similar functions. I would still lift these components up on one side and measure them as I have run across color codes that were wrong for the value of the part and yet the part was of the correct value. I think in China if they catch that the color code is wrong they go ahead and use the part because the part is good.

[fzabkar]

Re: Wine Fridge Power Board

Hello, I am having problems with this board, some components are totally burnt and i would like to know the specs of them, can you guys help me? the components are:

L1
R34
R35
R36
D10

I think that there may be errors in the hand drawn circuit diagram, but ISTM that there is enough symmetry in the circuit to enable the values of some of the damaged components to be inferred from other components.

R35 = R38
R34 = R37
D10 = D12

[keeney123]

Re: Wine Fridge Power Board

So the best spec. I can come up with is in post 106 schematic I drew up. I do not have the board, I am going from a picture. I tried to have the numbers verified by the person who has the board, but he has not responded back yet.

[fzabkar]

Re: Wine Fridge Power Board

Sure like to know what that part is inside that tubing ...

It appears to be a wire link that programs the fridge for 120VAC operation. Removing the link would configure it for 240VAC.

[dunkel]

Re: Wine Fridge Power Board

Hello, I am having problems with this board, some components are totally burnt and i would like to know the specs of them, can you guys help me? the components are:

L1
R34
R35
R36
D10

Thanks in advance