Print this test point list out. Check each test point and write down the value. With a Bally/ Stern of this era the problem will usually present itself or show you where to look after checking all the TP values. Always check the ground TP for continuity.

Rectifier Power Supply Board:
• TP1 = +5.4 vdc (AS2518-18 version), +6.5 vdc (AS2518-49 & -54 versions) feature lamps.
• TP2 = +230 vdc (score displays) with connector J3 attached, 150 vdc with J3 disconnected.
• TP3 = +13 to 16.5 vdc with connector J3 disconnect, +12 to 14 vdc with J3 connected. This voltage will become the +5 regulated voltage.
• TP4 = 5.7 to 7.3 volts AC (general illumination)
• TP5 = +43 vdc (solenoid voltage)
• GND = Ground

MPU board:
• TP1 = +4.9 to 5.2 vdc
• TP2 = +12 to 14 vdc
• TP3 = +21.5 vdc (comes from +43 vdc solenoid voltage). NOTE: If a -133 MPU board (with a 1N4148 diode at R113, as used on Granny and the Gators, Baby Pacman, & Grand Slam), TP3 will read about 5 volts DC.
• TP4 = Ground
• TP5 = +4.9 to 5.2 vdc

Solenoid Driver/Voltage Regulator board:
• TP1 = +4.9 to 5.2 vdc
• TP2 = +190 vdc (but often turned down to 170 volts to increase score display life).
• TP3 = +4.9 to 5.2 vdc
• TP4 = +230 vdc
• TP5 = +12 vdc to 16.5 vdc
Note if TP2 and TP4 are both 230 vdc, then the High Voltage portion of the solenoid driver board is not working and needs to be repaired.

Lamp Driver board:
• TP1 = +4.9 to 5.2 vdc
• TP2 = Ground
• TP3 = (only on AS2519-23 version)

Auxiliary Lamp Driver board:
• TP1 = +4.9 to 5.2 vdc
• TP2 = Ground

Display Driver boards:
• TP1 = +4.9 to 5.2 vdc
• TP2 = +190 vdc
• TP3 = Ground

Try taking your displays out and re-flow the header pins, they suffer from cracked joints. Also check the pins in the plug for corrosion or broken pins.