The game plays with no sound at all. The sound board appears to boot and the 5 V test point on the power supply looks close to normal.

No sound though the sound board boots: 5 V reaching it is low, adjust the trim pot

Cause: The 5 V actually arriving at the sound board was low enough that it would not produce sound.

Checks

• Measure 5 V at the sound board itself, not only at the power supply.
• Check the sound board's other supplies (+12 V and -12 V) against the manual.
• Do not condemn a bridge rectifier from in-circuit diode readings; readings in both directions are normal while it is still in the board.

Fix

• Adjust the 5 V trim pot on the power supply until the sound board sees about 5.0 V, then recheck the other boards' 5 V.

The backbox has high voltage for the displays; keep clear of the display supply while adjusting with the game on.

Systems

• Gottlieb System 80B

Games

• Monte Carlo

Related tips

• System 80B sound board LED stays dark until the CPU boots
• The System 80 sound board generations by game number
• Gottlieb System 1 and System 80 power harnesses look alike: check before fitting
• Sound/speech power supply MA-149 parts
• Ground mod step 7: sound/speech power supply ground
• Sound board won't boot with the music board attached: fake YM2151 chip
• Very quiet sound with a 60 Hz hum: bad capacitor on the A5 board

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