Thanks, I want to believe that the lower transformer is actually used backwards on purpose, like the top transformer provides a variable voltage that is regulated on the right side of the circuit, and a proportional voltage is applied to the right side of the lower transformer, which in turn drives and modulates the top transformer to alter the 0-12v voltage to the peltier cell & fans?
Not sure thou...
edugimeno
Badcaps Veteran
Last Activity: 04-22-2025, 12:49 PM
Joined: 05-30-2017
Location: Spain
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Hi again!
Im still investing some time, not much as Im busy lately... on this project
My first issue, is that I dont' reallly understand how this whole circuit works,.
I've found the schematic, attached as 2 images.
So there are 2 main transformers, small and large. Small has 1 dual winding and another single winding on the primary side. Center tap on dual primary winding seems to be controlled by twin mosfets, 1 drives to Vcc, 1 drives to GND. But then the top winding comes in series with the other transformer, and this is what I don't understand why they get interconnected....Leave a comment:
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You mean the diode, that looks like it has a thin line across? I think it's just a camera reflection, but I tested it with my MM and it checks good in diode mode 0,5v- infinite on both ways
Thanks
Its got to be something closer to the chopper,,, I believe...Leave a comment:
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ANyone? Thanks!!Leave a comment:
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Ok Im completly lost at this time... Here's how it went:
I found a proper 60W incandescent bulb and a socket
I bought all the suspicious capacitors, including the HV pair to make sure they are the same capacitance
I went to where I have this board and put all the news caps in, replaced the mosfet, added the bulb in series and powered up
Nothing happened not even noise.. Mains current wasn't going too far. The fuse was blown too!
Ok replaced with a similar vale and tried again. 0,3v at 12V outputs...Traced from start to end. 160V DC on each HV capacitor, this is good....Leave a comment:
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Yes this one feeds a peltier cell thats supposed to be 80-100W I believe...But I will be testing it without the peltier cell as I brought home the board only. I just came back from the shop to buy all caps, will test them later tonight, still need to find the bulb, nothing at the shop, will see at my dad's houseLeave a comment:
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Alright, will be back with some news hjopefully in a couple days, tnxLeave a comment:
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Ok I'll get the caps from my local shop tomorrow monday and try it. What's the wattage used for the dim bulb series tester? It's going to be hard, filament bulbs have been forbidden to be sold here in Spain for many years now, I haven't seen a non LED bulb for a looong time
60W is fine?Leave a comment:
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Alright, I will get those. And what do you think of the other questions... Should I just turn it on as soon as I replace the caps? What could have caused the mosfet to instantly burn?
ThanksLeave a comment:
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Ok the replacement mosfet arrived and I put it back in place. I measured resistance everywhere and found no short on diodes, and places that looked like shorts it was the transformer coil that was in parallel...
So what could be wrong before I turn this on again? The apparent short near the dual schottky diode was not a real short, both 1&3 legs measured low ohm but it was the secondary of the transformer. I took the dual schottky diode out to measure it and it was ok (infinite backwards,, 0,188 oh direct on both diodes).
I have a bunch of small capacitors out of...Leave a comment:
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Ok will do that today. Also I read on another post on this forum about this same that one guy fixed (Im talking about the original issue, once I replace the fried mosfet) 3 boards like this just by replacing C8. Will check that too
[URL="https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-appliances-and-other-household-electronic-stuff/39331-wine-fridge-power-board?p=1145211#post1145211"]LINK[/URL]
Also, trying to analyze the function of this board...As I don't have a valid schematic of it yet..I believe there should be a...Leave a comment:
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Ok I see. Yes those pads are looking bad but the connection is ok, I will redo them anyway.
There is a 0Ohm across lead 1&3 of the schottky diode but I believe this is internally created in the diode...oh wait, I just checked the datasheet and it's not a single diode between lead 1-3 to lead 2, its a twin diode so leads 1&3 should not have that short... I will recheck that but someone mentioned that such a short in the secondary wouldn't make the mosfet in the primary burn immediatly...
The new mosfet is in its way but aside from removing the short in the secontary, I need...Leave a comment:
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Thanks a lot.
The part placed on the black large heatsink is labeled STPS2045C, you are right, it's a schottky diode, I will test it later on out of the board. Also I can't really tell which bad solder point you are refering to, can you explain maybe drawing on one of my pictures?
Thanks a lot!...Leave a comment:
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Are we talking about the guy circled in red in this picture? Testing on-.board it measures 0,5v in one direction and 1.2v in the other. His "twin" on the other transformer has near zero values on tboth ways, but the suspect side has a blown mosfet connected to it..
So you believe the short I made in the secondary should not be enough to blow the mosfet driving the primary?
Thanks!...Leave a comment:
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Yes, what looks weird is that the short right now is at the SECONDARY of the transformer powered by that mosfet, not the primary. Would a short in the secondary make the Q driving the primary blow so hard? and quick? Or should I look for something else. Maybe I should try to link all this to the original issue of the clicking noise and only 2-3V delivered at output...
ThanksLeave a comment:
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Updates... I fu**d up... Went there (I have it at my country house), checked for visible sparks at full dark. Nothing on either side
Used the wood spoon method that suggested, and found the noise coming from the larger transformed in the middle of the board.
Took it out of the chassis and started redoing some solders around the transformers area. Put it back in place and turned on. Bang...At least it was quick and felt like whatever exploded was instant and damaged no more.
Found one of the 2 (probably) chopper transistors split into 2 pieces. You can see the pictures. Turned...Leave a comment:
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Gotcha!! I understand now. Ok yeah I will 1) try to see if I can spot the spark under no light, and 2) see if I can hear what part is having that noise with that method, thanks!...Leave a comment:
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Thanks! But I got a bit lost on the wooden spoon usage for this...
Could you please elaborate?.
Thanks!!!...Leave a comment:
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That could be, I thought It was a heavy switching noise but it could be arcing. I Will check in full darkness
If so whats the common source of arcing? Bad solder?
And posible solution?
Thanks!!...Leave a comment:
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ok so I should change those smaller ones by the low voltaje side right?
Would that relate to the high temp.at the choppers heatsinls?
Also when the screen has already settled, the chirping sound keeps gong and still 3v present at the fans and peltier output...makes sense?
Thanks...Leave a comment:
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