With a replacement MPU and LED bulbs, the lamps flicker and the displays have a slight rolling shimmer.

LED lamps flicker and displays shimmer with a replacement MPU: adjust its trim pot

Cause: This game keeps the MPU very busy with extra displays and lamps. The display interrupt timing on the replacement board was off, which upsets the triac-driven lamps.

Checks

• Check whether the replacement MPU has a trim pot for the display interrupt.

Fix

• Turn the MPU's display interrupt trim pot slowly (usually clockwise) while watching the lamps and displays until both are steady.

Systems

• Bally MPU AS-2518-35

Games

• Mr. & Mrs. Pac-Man

Related tips

• Fit the replacement MPU LED the right way round
• New replacement MPU boards exist
• Flicker but no first flash
• MPU LED never lights at all
• Strip the MPU to three chips to get the first flicker
• Dark MPU LED: follow +12 V through R29 and Q2
• Leave the ROM jumpers alone until the LED flickers
• MPU stops before the 7th LED flash (no 43 V)

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