Special solenoids: switch-fired on CPU Rev 1/2, CPU-fired on Rev 3
On CPU revisions 1 and 2 the six special solenoids (pop bumpers, slingshots and similar) are fired directly by a simple switch-sensing circuit. From CPU revision 3 (Back to the Future on) the CPU fires them, but the old circuit was kept on the board for backward compatibility and can still fail. If connector CN18 at the upper right of the CPU board has a plug in it, the game uses the old circuit; no plug means a CPU-controlled revision 3 game.
Systems
Related tips
- Special solenoid signal paths SS1-SS6 on the CPU board
- Version 3 CPU fires special coils once per switch closure
- Testing the legacy special-solenoid circuit at CN18
- Special coil locks on only when a game starts or diagnostics begin (pre-Rev 3)
- The solenoid L/R select relay and transistor Q29
- Solenoid driver layout: 16 multiplexed plus 14 constant
- Bank select relay and CPU transistor Q29
- Multiplexed L/R (A/B) banks and wire colours
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)