Keep spare 6800, 6821 and 5101 chips
Once the reset section tests good, a locked-on LED is often cured by a new 6800 CPU at U9 and a new 6821 PIA at U11. Both are cheap and worth keeping as spares, along with a few 5101 RAMs, which fail often on these boards.
Systems
Related tips
- Leon's test EPROM fitted but the LEDs do not start flashing
- Two flashes only: U8 5101 RAM
- Three flashes only: U10 PIA
- Four flashes only: U11 PIA, R134 or a bad display
- One PIA output does not toggle in the test EPROM test
- Good MPU stays LED-on with a PC power supply
- Bally-35 MPU: remove the on-board rechargeable battery before it leaks
- 5101 RAM at U8 fails often; speed matters
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)