At power-on the display reports a sound ROM checksum fault or a "sound board interface error", though the game otherwise seems to run.

"Sound board interface error" or sound ROM checksum message

Cause: Usually a bad sound ROM; sometimes a dirty ribbon cable.

Checks

• Reseat all ribbon cables.
• With the game off, remove all the sound ROMs; on power-up you should hear two bongs instead of one.
• Power off, fit only the first sound ROM (U9 pre-DCS, U2 DCS, S2 WPC-95) and power up: expect three bongs.
• Add the rest back singly; whichever ROM brings the message back is bad.

Fix

• Replace the sound ROM that brings the error back.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• All sound stops when a game starts, two error tones at boot: reseat CPU chips
• Sound board RAM error at U9, wrong call-outs or no sound: replace the U9 RAM
• The WPC sound board runs on its own
• Sound board beep codes at power-on (pre-DCS)
• No audio output at all from the sound board
• Pre-DCS sound board faults by symptom
• DCS or WPC-95 sound faults: amps and op-amps

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)