Safe first power-up of an unknown game

Steps

• With rectifier J1 (playfield) and J3 (backbox) unplugged, power on. Check TP1-TP5 (about 6.4 V on -18 or 8.2 V on -49, 195 V, 11-16 V, 7.5 V AC, 47 V). Rebuild the supply if any is out.
• Reconnect J1 and J3, but unplug MPU J4, driver board J1, J2 and J5, and pull the high-voltage fuse.
• Power on and measure driver TP2: 160 to 190 V. If higher, measure TP4; if TP2 and TP4 are both around 230 V the HV section is blown and must be fixed before refitting the HV fuse.
• Recheck the rectifier test points, then do the C23 ripple and +5 V checks before plugging in J4.

The score display supply runs at 170-230 V DC; keep hands off the rectifier and driver boards with power on.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• First checks for any missing voltage
• How the pre-Xenon power supply works
• A missing test point voltage: what to check first
• Make sure the power cord has its ground prong
• Differences between the -54 and -132 power modules
• Line filter, power switch and service outlet
• MPU LED lit solid: check +5 V first

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