All music, sound effects and speech were missing on a replacement CPU board, while the rest of the game worked.

No music, effects or speech: failed 6821 PIA for sound on the CPU board

Cause: The 6821 PIA that passes sound commands from the CPU to the sound board had failed.

Checks

• If the PIAs are socketed, swap the sound PIA with another 6821 on the board (for example the display one) as a test.
• If sound comes back and the other function now misbehaves (here the displays went garbled), the moved chip is bad.

Fix

• Replace the bad 6821 with a new one and put the original chips back in their own sockets.

Systems

• Data East CPU Version 1/2

Games

• Torpedo Alley

Related tips

• Combining two-chip CPU code into one 27512 for 5C
• Torpedo Alley: CPU and display EPROM types and latest versions
• Segments missing or stuck on: CPU board PIAs 9B and 7B
• CPU board PIA positions and jobs
• Replacement battery holder for the CPU board
• Program runs but the PIAs never respond
• Missing VMA signal from corroded traces
• Other CPU jumpers and what they set

Source: Pinball Repair help group!! (Facebook group)