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"singing" board (audible noise), how to pinpoint?
Conrad Hoffman:
Do you have any much faster clocks that are about 5 kHz apart?
richnormand:
Years ago I had a similar issue on a large board with some high voltage on it too (3-4kV). I could hear it fine but the high pitch made it hard to locate. It was at a higher frequency but with several lower harmonics that were angle sensitive. I used an electret microphone and spectrum analyser and got a good signal. Due to the high frequency there was a complex pattern in intensity distribution in the far field due to interferences. The interference pattern was pretty sharp however either indicating a near point source with diffraction pattern or multiple sources in phase with each other.
Solution: a 6 foot length of 1/4" tygon flexible tubing. One end in my ear and the other one taped to a small stick scanning the pcb at a few mm height of components while using the length of the tube to stand away from the assembly.
Turned out to be a ceramic capacitor that was signing.
People suggesting using a microphone could consider coupling a long flexible tube to it to probe the nearfield and isolate individual components.
Best of luck with it!
roland:
Guys, thank you all very much for your numerous great suggestions. I have ordered some stuff (microphone, tubing, stethoscope) and will let you know when I've found the culprit. Thanks!
RoGeorge:
The rod I was telling can be a simple thin, dry and stiff stick from outside, the tubing can be a simple sheet of paper rolled, it will act as a rod and as a tube in the same time.
NiHaoMike:
--- Quote from: KMoffett on February 21, 2020, 08:44:14 pm ---Get a cheap stethoscope. Remove the head (bell and diaphragm). Just use the tube to snoop out noises. Very handy.
--- End quote ---
Or 3D print one.
https://hackaday.com/2018/03/17/3d-printed-stethoscope-makes-the-grade/
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