Argh -- Galaga whine

ieure

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My Galaga has had a noticeable annoying high-pitched whine coming from the speaker since the day I got it. I've recapped both the 90414 power supply board and the game board, and the whine is still there. I unplugged the monitor to see if it was that. It's not. I unplugged the marquee lights to see if those were interfering somehow. They aren't.

Adjusting the game volume does not change the volume or pitch of the whine. The only thing that makes it stop is unplugging the speaker.

What on earth is this and how do I stop it?
 
Check grounds for starters... but its admittedly one of the hardest things to fix...

Big blue or other capacitors in the power lines, speaker itself...
maybe try another speaker with short shielded wires and see what it does

Phoenix and star wars are my culprits
 
I would look at the input to the amp with an oscilliscope.

I had a problem with something like this before. One case it was the speaker wire was re routed too close to a floresent light and some other wiring. The other was very strange, noting I did worked. I changed caps. variable resistors connections speakers. It was not untill I changed the amp did it tone down but never completly went away.
 
Following up on this… The plug on the power cable had been replaced before I got this game. Tested continuity between the ground pin, all good. Checks between that pin and the usual places for ground (e.g. PCB rack) all checked out.

Swapped the AC line filter, since I've heard that those can cause similar issues. No change, still got the whine.

To recap:

* Grounds are fine
* Replaced ALL caps on the 90414 PCB — should be fine
* Replaced ALL caps on the game PCB — should be fine
* There are no fluorescents in this cab; can't be that
* Unplugged the line for the marquee lights (6v AC), which runs near the speaker wire. No change.
* Unplugged the monitor. No change.

Guess at this point I need to swap the PCB and see if the symptom is in the cab or on the board.
 
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