treadmill pcb/ burning

Thread Starter

paddy mallett

Joined Nov 12, 2014
10
i have a pulse fitness pcb from a treadmill, i changed the large cap 15000yf 25v which was blown,
the treadmill now starts up but there is smoke coming from 2 small 470 resistors to the left of the relay switch, between r7 and r13
can anyone tell me what might be causing this, would it be a faulty relay or somthing else,
thanks in advance for any help
 

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No way to know for sure without a schematic and some voltage readings. One thing I notice from the picture is how dark the solder is on the power transistor on the far left that looks as if it mounts separately. I looks like it has gotten very hot.
Make sure that wherever it mounts that proper heatsinking is occurring when mounted. It's also possible that there is an electrical isolation at that point also (mica barrier). If that is compromised I can understand smoke coming out of things ;-(
 

Thread Starter

paddy mallett

Joined Nov 12, 2014
10
No way to know for sure without a schematic and some voltage readings. One thing I notice from the picture is how dark the solder is on the power transistor on the far left that looks as if it mounts separately. I looks like it has gotten very hot.
Make sure that wherever it mounts that proper heatsinking is occurring when mounted. It's also possible that there is an electrical isolation at that point also (mica barrier). If that is compromised I can understand smoke coming out of things ;-(
thanks i will check that out
 

bwilliams60

Joined Nov 18, 2012
1,247
If those two resistors are near the large transistor, I would be checking the transistor for short. What is the number stamped on the transistor (Mosfet)?
 

Thread Starter

paddy mallett

Joined Nov 12, 2014
10
Ok thanks for all the help , i got it sorted , i changed the 2 bridge rectifiers, the 50n06 mosfet, bdw93c transistor and l78so5cv, and everything is running good, just writing up here what i replaced in case someone else has the same problem. oh i also changed the large capacitor 15000uf 25v which was the only part that was showing any obvious fault to start with. thanks again for anyone who gave me any advice
 

bwilliams60

Joined Nov 18, 2012
1,247
Just out of curiosity, were all the components you replaced defective? Did any of them show any visible damage? Just curious. Unusual for the large cap to go up in smoke.
 

Thread Starter

paddy mallett

Joined Nov 12, 2014
10
the large cap had blown , it was bulging, and when i replaced it , if i shook it you could hear it rattle, the other components all looked good , and tested positive apart from mosfet, it was giving various readings when i checked it so i think that was what was causing the problem,
 
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