[sdiy] Microphonics

Tim Ressel timr at circuitabbey.com
Mon Jan 22 17:15:05 CET 2018

Got a weird one...

An oscillator I designed is whining. Well, some units do it. It is faint 
and you have to have your ear right up against the board to hear it. But 
an end user complained so we had to investigate. Other weirdness ensued 
but we got the customer taken care of.

My question is: how to find where the whine is coming from? I tried 
using a microphone but could not pick anything up. This is an ASM-1 type 
VCO (saw core) so there is a pulse train present. That could explain the 
mic not picking it up. I tried putting my finger over various components 
on the board with no luck. I thought about using an accelerometer but it 
would have to be high sensitivity and low mass to work.

I am at a loss.  Any thoughts?

--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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