The volume is stuck at maximum and the volume buttons have no effect.

Volume stuck at full and buttons do nothing (pre-DCS)

Cause: The X9503 electronic pot at U5 has failed, or capacitor C18 (47 mfd 25 V) next to it.

Checks

• Test U5 and C18.

Fix

• Replace U5 or C18; or remove W9 and fit a manual pot on J507 (pin 2 centre leg, pin 4 ground).

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics

Related tips

• Pre-DCS sound board A-12738
• Pre-DCS sound boards are tuned per game
• Pre-DCS sound cuts out after the game warms up
• Pre-DCS speakers pop and get damaged, LM1875 runs hot
• Sound board beep codes before DCS
• Fitting a manual volume pot to the A-12738
• Adding a line out to the A-12738 sound board
• Sound board fuse F501 blows at power-on (A-12738)

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