After the game has been on for 20 to 30 minutes, all the speech (game start voice, visor and other call-outs) disappears while other sounds play. Switching off and on brings it back for another 20 to 30 minutes.

Speech drops out after 20-30 minutes, back after a reboot: speech chip on the MPU

Cause: On this game the speech is generated on the MPU board. The 55536 speech chip was failing as it warmed up. The 1458 op amps and a 10 uF cap in the same circuit, the -15 V supply and the sound ribbon cable can cause similar symptoms.

Checks

• Note that only speech is lost, which points to the speech circuit on the MPU rather than the sound board.
• Reseat the ribbon cable between the MPU and sound board, and check the -15 V supply.
• When the speech is gone, gently cool or tap parts of the speech circuit to find the one that is heat-sensitive.

Fix

• Replace the 55536 speech chip (socket it); if that does not cure it, replace the 1458 op amps and the small electrolytic caps in the speech circuit.

Systems

• Williams System 11A

Games

• Pinbot

Related tips

• Speech very faint on a type 2 board
• Lamp types found in EM games
• Pinbot sound suddenly dies but the amp hisses
• Which System 11 sound board each game uses
• D-11297, D-11298 and D-12338 sound boards
• The D-11581 sound board: chips and ROMs
• Replacing the obsolete 55536 speech chip
• CPU sound diagnostic switch SW1 results

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