Author Topic: Noisy / failing output inductors in a SMPS  (Read 238 times)

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Offline Andersounds

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Noisy / failing output inductors in a SMPS
« on: April 26, 2019, 08:22:51 pm »

Thought someone might find this fault interesting.

I inadvertently overheated  the inductors on the +/- 18v rails of a basic SMPS and they failed, the outputs went very noisy, sounded like white noise with some jittery square content..

Didn't expect these green blob inductors to fail from heat, the bigger ones are 150uH and the small one is 20uH, so if you see similar inductors on a really noisy supply try swapping them out, as just measuring them didn't show up the fault.

Background info long version:
Was doing a routine recap on an 80's switch mode power supply, I have done this refurb many times before zero issues, this time however I used hot air to loosen up the old hot glue / gunk that was holding the capacitors in place, powered it up and there was excessive noise on the output of the audio circuit, put it to one side and moved on to another one, same thing happened, after swapping various parts and getting nowhere I took out the inductors and measured them all looked good, eventally got some known good ones and swapped them out, then circuit was quiet again Wasn't a component I would have suspected.

PS thanks to EEVBLOG members for helping me with my last post, got me on the right track for the repair, so I'll share any findings I make here to contribute.  :-+

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