IIGS - chirp sound when I shut off power supply

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Last seen: 4 days 32 min ago
Joined: Nov 25 2020 - 14:55
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IIGS - chirp sound when I shut off power supply

I have a IIGS ROM3 that makes a chirp sound from the power supply when I switch it off.  Otherwise, everything works fine.  Its a Dyna Comp LR62786 power supply shown here:

https://stayornay.com/mac84tv/repair-guides-documents/apple-iigs-power-s...

I've opened it up and don't notice any buldging capacitors.  I'm OK with doing the soldering work, where I struggle is ordering the correct parts.  For example on the above parts list, I can't even find item #3 100uF capacitor with 7mm pitch that meets the space requirements listed.   I can't find a capacitor kit for this power supply either.

Any tips on finding the source of the noise?

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Last seen: 4 days 32 min ago
Joined: Nov 25 2020 - 14:55
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IIGS - chirp sound when I shut off power supply

One other data point - the chirp occurs even when power connector disconnected from logic board (no load).

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Last seen: 2 weeks 1 day ago
Joined: Jun 16 2020 - 16:58
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Per your tests, the chirp

Per your tests, the chirp comes from the PSU itself. It may be simply a coil buzzing while the switching dies off. I wouldn't worry too much about it but one thing you could do is to reflow all the soldering joints on the PCB. Sometimes micro-vibrations may cause a crack in the solder, allowing the vibrating component to vibrate more and to generate sound. 

 

As usual, please remember that in that power supply there are lethal voltages: I do not advise you to open and to work on it and you should not follow my recommendations.

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