Sound works at power-up but disappears completely as soon as a game starts or the service menu is entered. At boot the game gives two error tones, which point to a sound ROM (U2) fault.

All sound stops when a game starts, two error tones at boot: reseat CPU chips

Cause: Not a sound board fault: the sound board worked in a swap test. The problem cleared after the CPU chip and game ROM were removed and reseated and the memory was reset to factory settings, so a poor socket contact or corrupted settings on the CPU board is the likely cause.

Checks

• Swap in a known good sound board, or try this one in another game, to rule it out.
• Reseat the CPU to sound board ribbon cable.

Fix

• With power off, remove and reseat the CPU chip and game ROM on the CPU board.
• Do a full factory reset (pulling the batteries clears everything), then set the game up again and reboot.

Systems

• WPC DCS

Games

• Star Trek: The Next Generation

Related tips

• WPC sound board versions
• The WPC sound board runs on its own
• All flippers fire at power-up and blow the 50 V fuse: aux board ribbon upside down
• Deafening hum at power-on: cracked ground trace at the DCS sound board filter caps
• Reading the CPU board LEDs at power-on
• CPU board completely dead
• Dead CPU: check the reset and IRQ lines
• CPU board from an early game won't boot: ROM jumper W1

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