Soon after a replacement CPU board is fitted, the game randomly plays a strange sound while sitting in attract mode. It otherwise plays normally.

Random stray sounds in attract mode after changing the CPU board

Cause: The sound board is picking up noise or mistimed data on the shared bus and treating it as sound commands. The combination of CPU board, sound board and ribbon cables is sensitive to bus timing, and weak power from a rough driver board can make it worse.

Checks

• Reseat or replace the ribbon cables between the CPU, driver and sound boards.
• Put the original CPU board back (or try the CPU or sound board from another WPC game) and see if the noise stops.
• Check that the sound board voltage regulators are not running very hot.

Fix

• Go back to the CPU board that does not cause it. If a particular pairing keeps doing it, the bus transceiver on the CPU board or the latch on the sound board are the parts usually changed.

Systems

• WPC Fliptronics

Games

• Fish Tales

Related tips

• WPC sound board versions
• WPC-89 sound board layout
• 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
• Sound board RAM error at U9, wrong call-outs or no sound: replace the U9 RAM
• Pre-DCS sound board faults by symptom
• WPC sound board silent, no power-up bong: try the RAM first

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