Electronics > Repair

Bench supply shuts off randomly

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Circlotron:
Got a 15 volt 40 amp SMPS bench supply that has recently started shutting off for no apparent reason. Turn it on and leave it running with no load and anything between 5 minutes and 2 hours it just goes off. Display goes out too. Like it was unplugged from the wall. Turn the AC mans off and wait for a short time and turn it back on and away it goes until next time it decides it's had enough. If you turn it off then back on too soon it doesn't restart so it sounds like it might be *wrongly* tripping some kind of overtemp or overload shutdown.

is anyone familiar with these PSUs? Likely they are packaged and sold under various names worldwide. Anybody got a schematic? I'm quite okay with working on SMPSs.

fqahmad66:
First thing will check if anything smells burning. then feel if something is getting hot and lastly tighten all the heatsink mounted parts screws. If that does not point to something then look for a schematic.

timenutgoblin:
There's an EEVBlog video on YouTube of this PSU.

https://youtu.be/bX8IIjf15qY

Check the description of the video.

eurgenca:
Yeah and you have schematic under files.

https://eevblog.com/files/SPS9400_ServiceManual.pdf

Circlotron:
Looks like I might have it sussed.
On the underside of the board there was a small amount of corrosion between the adjacent drain and feedback pins of the TOP222 switcher IC. Plenty of peak volts on the drain so it wouldn't take much to conduct over to the feedback pin and shut it down. Been running for 2-1/2 hours now. When it was first handed to me it would only run five minutes my my bench. Let's see if it's still running when morning comes. 10:40pm here now.

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