Running Leon's test EPROM with the boards still in the game

Steps

• Bench testing is preferred, because the test code switches every PIA output on and off.
• If testing in the game, pull power supply fuses F1 (display high voltage), F2 (coils) and F3 (lamp matrix), or unplug every CPU and driver board connector except CPU connector 1J2.
• Also disconnect power to the sound board, since the toggling outputs can trigger sounds.
• Without F3 removed, the CPU-controlled lamps get a steady 18 V and burn out at once.

The display high voltage on F1 can give a dangerous shock; remove it before probing.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Leon's test EPROM: what to burn and where it goes
• Use Leon's test EPROM, not the Williams one, for boot faults
• Leon code running but LEDs dark: bad CPU PIA IC18
• Leon's test EPROM fitted but the LEDs do not start flashing
• One EPROM instead of three
• A PIA output fails Leon's test but the PIA is good
• EPROM types used for System 3 to 7 game code
• Leon's memory test results (versions from 11/01/03)

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)