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Strange board behavior when switching power supplies (photos.app.goo.gl)

submitted 1 year ago by [email protected] to c/[email protected]

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This photo shows the power conversion side of two versions of the same board. Input is up to 60V DC, board converts to 5V and then down to 3.3V.

The top board works correctly all the time. But the bottom board has strange issues. Everything works perfectly when I connect it to my bench power supply at 53V. The board powers up with no problems. When I connect it to the daisy chain of other boards, it suddenly will no longer power on, despite ~54V being passed through correctly to downstream boards.

This is a real head-scratcher for me, and I'm having trouble making sense of it. I'm not so much looking for The Solution as to what steps I should take to troubleshoot this. There were some issues attaching the image, so in case it doesn't show up.

https://photos.app.goo.gl/MCx7Q4BDbKTv68EJ8

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[–] [email protected] 1 points 1 year ago

Correct, it's a switching converter, the MAX17640. 5V is not powering up (getting ~2V out) and then the 3.3V LDO is not powering up.

I put an older variant daisy-chained board before and after the newer board. Both of the older ones come up, but the newer one doesn't.

I will check soldering disturbances and put my scope on the input line to see if there's a lot of noise. Thank you!