With only U9, the test EPROM, U15 and U16 in place, the test LED stays dark or steady.

Test EPROM fitted but the test LED does not flash

Cause: Usually a dead reset section, or jumpers that do not suit the EPROM in U6; also a bad 6800 or a fault on the clock, address or data lines.

Checks

• Meter U9 pin 40: under 2 V means reset is held low.
• Jumper TP5 to U9 pin 40 to force the CPU out of reset; if nothing happens, try another 6800.
• Check the U9 and U6 signals listed in the next entries.

Fix

• Repair the reset section, the jumpers or the failing line found.

Systems

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

Related tips

• What each MPU LED flash proves
• MPU LED locked on with no flicker: likely causes
• MPU stops before the seventh flash: check the 43 V at R113
• Good MPU stays LED-on with a PC power supply
• MPU boots only when U9 pins 39 and 40 are shorted
• Game reboots during play from slam switch noise
• Reading the MPU flash code
• What a good MPU does straight after the last flash

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