ms pacman board repair

chips4sle

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hi
i have a ms pacman board
everything works but sound. i have replaced the sound amp and all i still get the a thumping sound as she eats the dots and no background sounds
what next
jeff
 
I have diagnostic kit from Two Bit score. It appears that the 74LS259 chip at location 8K is involved with sound. Maybe yours is bad.
 
First make sure 1M and 3M proms are there. Make sure they are seated good too. Its possible one of them is bad, if they are out of circuit you should have no sound.
Thumping or hum is usually bad caps in the sound section. Start by replacing the cap closest to the amp, think its a 330uf. Thats usually the culprit. Do you have a logic probe?
 
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