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Old 08-12-2012, 09:48 PM   #17
vsmGuy
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Join Date: Jul 2006
City & State: southern california
Posts: 28
Default Re: Need tips in fixing APC 1500VA UPS having buzzing noise

Quote:
Originally Posted by Toasty View Post
I think the unit is fine and just gone a little noisy. You could replace them and the problem will remain. Because the noise is load variable, I would be scoping the output for spikes or looking further back in the circuit.
Toasty, I had hoped you were wrong and sunk ~$30 in parts to replace the caps (new, exact to original specs).

Noise remains - perhaps a bit louder than before

Quote:
Originally Posted by Toasty View Post
Try a paper towel roll as a "stethoscope" to pinpoint the noise. Try moving components with a wood or plastic tool to see if they're just resonating from the switching circuit. It's why PSUs have that glue/caulk around coils and caps.
The noise is very well from the 20uF cap we were discussing about - I can feel it vibrate when I touch it with a wooden stick.

Replacing the 20uF cap did not help - the noise remains, as I noted above.

I really like this unit and would hate to trash it, if it has become unsafe.

Any ideas if the unit is still good to power my Computer and Audio Receiver?

(these babies cost me $2k+ and I found it fit to put this APC workhorse to cover their back.)

I still wonder - why the noise? noise comes from the cap when the batteries are charging or when I make them discharge - could it be something because of the batteries themselves (but what?)
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