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Power supply 12V 20A

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Blisk

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I bought this power supply which have suddenly burned after I checked what was wrong I see that power transistor have been bad soldered.
So after that I changed what was dead it is circled in red and power supply works but problem is when I connect on 12V some device which takes about 5.5A power supply starts to heat up really badly. And it is 20A power supply so it should stand more than just 5.5A withouth heating.

After that I bought another one almost the same but have 30A 12V and when connect on it the same device which use 5.5A it doesn't get even warm.

Have anyone an idea what can be wrong with first, repaired power supply so it heats so much???
Largest transistor which heats up is STW12NK90Z.
powers1.jpg
 

try changing all the black bits which look like they have got hot - including the 8 pin dip control IC...
 

Easy peasy said:
try changing all the black bits which look like they have got hot - including the 8 pin dip control IC...
Click to expand...
All what is in red circle was changed, after power supply died.
 

Better you trace for the connections and try to change the components which is connected with the power transistor
 

The pcb shows an outline for hex-sided small transistors like the BC147 that I worked with 50 years ago. Then maybe this power supply design is that old.
 

check all the diodes, check underneath the pcb... check the o/p diode(s) aren't short... check everything you cn measure...
 

Audioguru said:
The pcb shows an outline for hex-sided small transistors like the BC147 that I worked with 50 years ago. Then maybe this power supply design is that old.
Click to expand...

yes this transistors are 2SC2655 and A1020 Y and S8550 and S8050
 

Easy peasy said:
check all the diodes, check underneath the pcb... check the o/p diode(s) aren't short... check everything you cn measure...
Click to expand...

yes I have already did that. Power supply works problem is because mosfet overheat. So it must be something which is partly damaged or something else.
 

did you really check the o/p diodes for a short? it is possible the Tx has developed a short in the sec....
 

powers2.jpg
you mean this one red circled??
yes I did and it looks ok. I have new one so maybe it will be good to replace it and than test?
 

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