You could have two of the 4 pin connectors wrong. If so, the game will play no sounds.

I only know this because I have done it before. Also, after owning 4 High Speed machines, I have learned from others that it's a common mistake when testing,swaping or just pulling boards to work on them.
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Double check pic here: see how the lower 4 pin connector is the gray shielded cable. If you switched them, you will get no sound.

These two connectors are both four pins. Easy to connect wrong...

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I don’t understand what you are saying. You posted before there is no sound now.

I know you said you don't have a scope but you can still check these steps off to confirm voltages and rectification. If you hear music, your amp and everything after the boards are good! :
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