The game suddenly stops booting and the MPU LED stays on solid. Test points and fuses look fine, and the MPU boots on the bench and in the game once the sound board is unplugged.

Won't boot with the sound board connected: bend out the IRQ pin 34

Cause: The sound board was dragging down the MPU through the IRQ line on the ribbon cable, a common failure of the timer chip on these sound boards. The sound board does not need that line.

Checks

• Unplug the sound board ribbon and see whether the game boots.

Fix

• Bend pin 34 on the MPU board's sound connector so it no longer makes contact with the cable (or use a 32-pin cable that leaves it out).

Systems

• Stern MPU-200

Games

• Meteor

Related tips

• MPU boots only when U9 pins 39 and 40 are shorted
• MPU shuts down or resets: broken C23 ground return wire
• Testing the MPU reset circuit at U9 pin 40
• Game reboots at random: R11 heating Q5
• Good MPU stays LED-on with a PC power supply
• What each MPU LED flash proves
• MPU on the bench always stops one flash short
• Bally/Stern MPU LED self-test: what to expect

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