Pac-Man cocktail loud hum (solved)

ColoFan

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I found a mouse-infested cocktail pac-man. Unfortunately there is a loud hum through the speaker. Other than that, the game plays fine. The hum disappears when the edge connector is unplugged.
It sounds to me like a grounding issue, but I'm not finding anything wrong.
Has anyone solved anything like this?
 
probably the caps on pcb set
arcadepartsandrepair.com sells the whole set
 
first check your fuses and fuse holder. Make sure all are clean and sitting tight. Then clean up your edge connector. After that check diodes at D7 and D8, then move on to the caps as r5g mentioned.
 
Thanks! Fuses are fine; I removed them and cleaned contacts. And the 2 diodes are good (open one way and 0.560 the other way).
I guess I need to buy some capacitors next :)
 
Curious to see what works, I had a Galaga that only hummed when it was closed, I rotated the PCB 180 to get the sound section further from the monitor and WALA no more hum.
 
Interesting, thanks. While I wait to order capacitors, I tried to take out the PCB from the cocktail pac-man, oriented it differently, moved it around. I heard some sound difference, and a few crackling in the speaker, but still a fairly loud hum in all cases. I also noticed that the board had been worked on. Edge connector A B 1 2 was rewired differently to the transformer CT, and a new jumper was added on top of D8 that connects to another 7V.
 

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AB12 are connecting to Ground. The 7v lines will be C-3 and D-4. Check the edge connector itself. See if the 7v pins are in decent shape. Is the other 7v wire at D-4 also clipped and wired into the same 7v line as C-3? Or something else leaving D-4 disconnected. That would cause a hum. If all is good there then hopefully caps help.
 
That makes sense, thanks! AB12, and C3 must have been bad on the edge connector and they cut them off and rewired them. D-4 is connecting to the usual 7V.
I'm expecting a cap kit from arcadepartsandrepair, fingers crossed!
 

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