The sound board makes only clicks where tones should play. After that is fixed, every sound plays at too high a pitch, even though the clock and frequency circuits measure the same as a good board.

Bally -32 sound board only clicks, then plays too high: U11 and the pitch resistor

Cause: The clicking was a common failure: an open leg on U11 in the frequency generator section. The high pitch came from the wrong value resistor at R35, where some versions of the board have a pitch trim pot.

Checks

• Check U11 for an open pin.
• Compare clocks and frequencies with a known good board.
• Look for the unused trim pot holes beside R35 and check that resistor's value.

Fix

• Replace U11.
• Correct R35, or fit a trim pot and jumper in the spare holes so the pitch can be adjusted. A larger C1 (about 300 pF in place of 100 pF) gives a wider pitch range.

Systems

• Bally MPU AS-2518-35

Related tips

• Sound died: Cheap Squeak clock test point stuck high, bad crystal
• Spare sound board works on the bench but is silent in the game: no -5 V, bad 7905
• Early sound boards carry 43 V too

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