The playfield general illumination is out while the backbox GI works. The GI voltage at J1 drops noticeably when the plug is connected and its wires get warm.

No playfield GI and the J1 wires run warm: one bad pin in J1

Cause: A poorly crimped pin (pin 8) in the J1 connector on the rectifier board was making a high-resistance connection.

Checks

• Measure the GI voltage at the pin with the plug off and on; a large drop under load points to a bad connection.
• Feel for warm wires or look for browned pins at the connector.

Fix

• Re-crimp or replace that pin in J1, and replace the header if it is discoloured.

Systems

• Stern MPU-200

Games

• Big Game

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