U15 CPU and U25 RAM substitutes
Early boards use a 6802 at U15; fit a 6808 instead. The U25 RAM is a 2k x 8 CMOS static RAM, 24 pin: 2016, 6116 or NTE2128; early boards list it as a 5177, which a 6116 replaces. A bad U25 can stop the board booting, so it is worth replacing early in a dead-board repair.
Systems
Related tips
- CPU still will not boot after the basics
- Electronic spares worth keeping for System 11 boards
- CPU RAM at U25
- Replace a failed 6116 RAM with a 6264
- Testing U25 RAM with Leon's EPROM
- System 9: is the sound fault on the CPU board or the speech board?
- CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
- No sound from a replacement sound board: its 6808 CPU socket was empty
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)