Sound is dead (sometimes with smoke) after reconnecting the backbox.

No sound after the 12 V plug went on the speaker lead

Cause: Some harnesses have a two-pin raw 12 V plug of the same style as the speaker plug. Joined to a speaker connector it burns out the A5 board's TDA2040 amps, LM340T regulator and MC3403 op-amp.

Checks

• Check the plug colours: raw 12 V is red/black/black, speaker is black/red/red.

Fix

• Reconnect correctly and replace the TDA2040 (or TDA2030) pair, LM340T (7805) and MC3403 (or LM324AN) on A5.

Systems

• Gottlieb System 3

Related tips

• No sound, or weak sound
• Parts on the A5 auxiliary supply
• No sound at all: check the -5 V regulator
• Both sound board LEDs dark
• Gottlieb System 3: loud screeching from the speakers: replace the sound board capacitors
• The A6 sound board
• The A20 auxiliary sound board

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