50 V coils on early System 11: under-playfield relay boards
Early games mix 25 V and 50 V coils, but the CPU drivers only handle the 25 V side. A small relay board under the playfield switches each 50 V coil: the CPU TIP122/102 pulls in the relay, which grounds the coil. From Big Guns on, TIP36 transistors on the auxiliary power driver board do this job instead.
Systems
Related tips
- 50 V coil dead on an early System 11 game
- Device switched by an under-playfield relay board does not work
- System 11 coil outputs
- Early System 11 games have no A/C banks
- 50 V coils on earlier System 11 games
- What changes when fixing coils on System 11
- Where the coil diodes are on System 11
- Fitting a replacement coil on System 11
Source: Repairing Williams System 11 Pinball 1986 to 1990, Deel 1, Clay Harrell (pinrepair.com)