Bypass the 8T28 data buffers IC9/IC10 on a pre-System 6A CPU
Steps
- Only do this if the board uses EPROMs; the buffers are needed only for 3624 masked ROMs. System 6A boards already omit them. Leave good buffers alone.
- Desolder IC9 and fit a socket.
- Fit Leon's test EPROM at IC17 and remove the 5101 RAM at IC19, which a wiring mistake here would destroy.
- Using legs cut from a scrap chip, plug pairs into the IC9 socket and solder each pair together at the top: pins 2 and 3, 5 and 6, 9 and 10, 12 and 13.
- Power up and confirm the board runs with Leon's code.
- Repeat for IC10, then refit the 5101 at IC19.
Systems
Related tips
- Identifying a System 3 to 7 CPU board
- What changed on the System 6A CPU board
- System 6 CPU board test points
- System 6 CPU board jumpers J1 to J6
- A System 7 CPU board can run any System 3 to 7 game
- System 3 CPU board ROM layout
- Which CPU boards can run which system firmware
- Obsolete chips on System 3 to 7 CPU boards
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)