Neither the A6 nor the A20 LED flashes with the game on.

Both sound board LEDs dark

Cause: The CPU-to-sound cable at CPU P4 is unplugged, or A5 is not supplying +12/-12 V.

Checks

• Check the plug at A1P4.
• Check fuses F10/F11 and measure +12 V and -12 V from A5.

Fix

• Reconnect P4, or repair the aux supply.

Systems

• Gottlieb System 3

Related tips

• The A20 auxiliary sound board
• The A6 sound board
• Sound needs the A1P4 cable
• No sound, or weak sound
• No sound after the 12 V plug went on the speaker lead
• Parts on the A5 auxiliary supply
• Constant hum or odd noise from the speakers
• A5, A6, A8 and A20 plug identification

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)