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Old 09-28-2020, 10:03 PM   #33
Senior Member
Join Date: Apr 2019
City & State: Deshler,Ohio
My Country: USA
I'm a: Knowledge Seeker
Posts: 148
Default Re: DC Power Supply QW-MS605D


The original MOSFET P75NF75 that pc7fan suggested was confirmed bad against the new part and was replaced.

I replaced the KA7500B IC next as there was no change in Power Supply in the hopes that the problem was the KA7500B. R_J believed from my description of the C24 Capacitor that it could have been impacted. I have a 10 pack of KA7500B and I swapped one out.

The cycling (video) stopped just prior to my replacing any part (the shorted MOSFET or the KA7500B IC) out of the blue.

Not sure why it stopped but there was a small flash near the T2 transformer and the cycling stopped. So the video is not the current scenario I see. I see zeros in both read outs and thats it.

Upon replacing the KA7500B and closer look there seems to be also damage now around Diode 15 (D15) which I believe is a 1N4148 not sure if it was related to my replacing the KA7500B (U4) or part of the original failure. I am guessing my roughness getting the KA7500B out of the board might have cracked it. (a real PIA)

So I orderd the Diodes and they are coming out of a location about 200 miles from my home so should be quick.

I am guessing I probably need to troubleshoot the board again once the diode is replaced to see where the failure is first appearing. Not sure really where to start so I am going to have to study the schematic to see how to break things down.

Any suggestions are greatly appreciated!

So far this has been a fairly cheap endeavor but I am starting to eye a replacement possibly the same unit and add the 2 year extended warranty.

Starting to feel like I am;

Not to mention my brother dropped off a 46 inch Flat Panel TV to see if I can get running and I have a spot for it

Thanks everyone for the help,
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