Bank switching does not work even though the Q7/Q8 driver tests good.
A/C select relay fails: welded contacts or cracked joints
Cause: A relay left energized for a long time by a shorted driver can overheat and weld its contacts. Its solder joints to the board can also crack.
Checks
- Inspect the relay solder joints on the board.
- Ground the Q7/Q8 tab and check that both the bank A and bank C devices on one driver can be fired.
Fix
- Reflow the relay solder joints.
- Replace the relay with a 24 V DC, 10 A, DPDT relay if it still fails.
Systems
Related tips
- How the System 11 A/C bank select works
- Which transistor drives the A/C select relay
- A-bank coil not working
- Whole A or C bank of coils dead
- Testing coil diodes on the auxiliary power driver board
- Later System 11 moved relay and diode boards to the backbox
- C-bank coil or flasher not working
- Wrong coils fire together (A/C bank game)
Source: Repairing Williams System 11 Pinball 1986 to 1990, Deel 1, Clay Harrell (pinrepair.com)