The power-up tune plays at half speed and scoring lags behind switch hits.

Everything runs slow (half-speed tune, late scoring)

Cause: Parts around the 555 timer U12 on the MPU, for example capacitor C16, have drifted and lengthened the interrupt period.

Checks

• Check the resistors and capacitors connected to U12.

Fix

• Replace C16 or the other drifted parts.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Garbled player 1 display and strange play from a bad 5101 RAM
• Using a PC power supply as an MPU bench supply: which wires
• All DIP switches off can start a self-test after boot
• Test EPROM: the least an MPU needs to run it
• Run Freedom or Night Rider on a -17 with 2716s at U1 and U6
• MPU LED never lights at all
• Power and ground pins of the main MPU chips
• U9 pin 2 (halt) is not high

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)