Could be the reset circuit is flaky and doesn’t always properly reset. When this happens the cpu won’t run and you get no sounds.

Pinwiki has a section detailing the reset circuit. You can check U1 pin 40 with a logic probe. On power up it should jump from low to high. Repeat the test over and over to ensure you are getting a consistent reset.

No U1? That’s the processor for the board. Without it you would have no sounds at all.

Not the MPU, U1 on the sound board. Your problem is not on the MPU.

Hold on. You do the reset test earlier mentioned on the sound board using U1. U1 is probably good.

Yea. Sound board red lead on pin40 of U 1 black lead on ground. You should see a voltage spike when you power up. Keep repeating a bunch of times to see if it’s consistent. The reset goes very low voltage for an instant then should stay about 5 volts.

Those readings make sense. When it booted with no sound it looks like it didn’t go low or no reset. Pinwiki lists all the components in the reset circuit. Check those and especially the big cap, I think it’s C1.

Also watch led on the sound board when you power on. Are getting 5 flashes every time? Even when you boot and don’t have sound?

The reset circuit on the sound board. Go to pinwiki and look at Squawk &talk troubleshooting.

From pinwiki: Make sure that the reset on the CPU chip starts low briefly and then goes high. With a logic probe, check pin 40 of U1. If the reset does not go high, suspect C1 (47uF 25v), CR1 (1N4148), R1 (27K 1/4w), U15 (74LS14), or possibly U17 (74LS155).