Power Supply Buzz

Peale

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I've got a power supply (standard Peter Chou style) that buzzes - right up until you place a finger on the metal case, and it stops.

Why does it do that, and how can I make it stop, aside from what I've been doing?
 
All screws tight? Check the screws attaching the switching transistors heatsink and the heatsink for the dual diode inside the power supply.

Make sure all outside case fastening screws are tight.

In rare instances I have seen the switching transformer itself make noise. A small dob of silicone glue inbetween the transformer coil and the laminations usually fixes that.
 
I've had this happen a lot with that type of PS and it has always turned out to be the fan vibrating the metal case.
 
I've had this happen a lot with that type of PS and it has always turned out to be the fan vibrating the metal case.

No fan!

Does it have to be your finger or is it just the weight of pressing down on it?

Nope, it's the finger. The gentlest of touches makes it go away.

All screws tight? Check the screws attaching the switching transistors heatsink and the heatsink for the dual diode inside the power supply.

Make sure all outside case fastening screws are tight.

In rare instances I have seen the switching transformer itself make noise. A small dob of silicone glue inbetween the transformer coil and the laminations usually fixes that.

Should be. I rebuilt it to use on a 60-in-1 project. All the voltages are fine, and it operates fine, it's just noisy. I'll have to crack it open to see where the buzzing is coming from. I'll swap it out for another unit that doesn't buzz, and troubleshoot it later.
 
Took me a few to figure it out, because once it was decased, it wouldn't make any sound at all.

And, weirdly enough, the bodies natural electrical field would make it stop, also. You'd just have to get close to it.

So...narrowed down where the sound was coming from with a paper towel tube. So I didn't have to get close (and shutting off the sound).

Didn't see anything obvious, but as I was sitting there contemplating it, I looked at the plastic sheet which goes under the pcb. The smallest spot on it was discoloured. I put it back over the pcb to see the area on the board which caused it. It was the transformer. One of the pads was floating, but not obvious until closely examined. It looked like a good joint, but wasn't.

Once the old solder was removed and the transformer resoldered, no more noise.
 
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