At power-on a few lamps light but the game never boots, even though the power supply fuses look fine.

Won't boot, only some lamps on: bad capacitor joints on the power supply board

Cause: Poor solder connections at the filter capacitors on the power supply board, so the supply could not hold up its outputs under load.

Checks

• Pull the fuses and test them with a meter rather than by eye.
• Measure +5 V at the CPU board with the game on; it should be close to 5 V (within about a quarter volt).
• Inspect the capacitor leads and connector pins on the power supply board for cracked or dull joints and leaking capacitors.
• Check the CPU board for battery damage while it is out.

Fix

• Reflow or replace the bad capacitor joints (and replace tired capacitors) on the power supply board, and reseat its connectors.

The power supply board carries line voltage on its input side; unplug the game before working on it.

Systems

• Data East/Sega CPU Version 3b

Games

• Mary Shelley's Frankenstein

Related tips

• Three backbox bridges on 192x64 DMD games
• Adding jumper wires across DB1 and C11-C14 (520-5047-03)
• Power supply board versions and their +5 V filter capacitors
• Power supply board versions are not interchangeable
• Z1 on the power supply is a varistor, not a diac
• Power supply CN1 pinout, pins 1-6
• Power supply CN1 pinout, pins 7-12
• Power supply gives no +5 V

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