Sound CPU pin voltages with the EPROM removed
With the EPROM pulled (IC2, or IC12 on System 6/7) and power on, measure the 6802/6808 (IC1, or IC9 on System 6/7): pins 2, 3, 4, 6, 8 at +5 V; pins 5, 34, 40 at about +4 V; pins 9-20, 22-25 and 37 about +2 V (pulsing); pins 21, 26-29, 33, 36 at 0 V; clock pins 38/39 about 0.2 V. A wrong output (such as an address line) usually means a bad CPU; a wrong input means tracing it back. Reset (pin 40) comes through a two-transistor delay; replace those transistors if it is missing.
Systems
Related tips
- Sound EPROMs work in either sound board type
- Sound board powered but not running
- Missing words or sounds from cracked connector pins
- Which sound board each game uses
- Sound board jumpers for 2K sound-only games
- Using the sound board test switch
- How System 3-6 games trigger sounds
- The sound board is its own computer
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)