The Special Solenoid circuit is protected by a single, 4A fuse. If a switch that drives a Special Solenoid gets stuck on, that corresponding coil locks on, and heats up. After several minutes, the coil gets so hot, that the insulation around the winding begins to burn and the coil resistance goes lower and lower until it's close enough to a dead short to finally cross that 4 Amp threshold and blow that fuse. Of course, by then the coil is completely ruined and will need to be replaced. Also the corresponding drive transistor (TIP) will likely be shorted, and the surrounding circuitry could also be compromised. All for one stuck switch.
Easy to install. Simply remove the plug(s) from 1J19, and connect this board onto the 1J19 header on the MPU. Then plug the connectors to J19 on the SSB. Connect the wire to any convenient Ground for LED indicators
The SSB fuses the power to each coil. Populate with 1-1.5 Amp fuses (I have personally had good luck using 1A SB fuses in these). The next time a special switch locks on, or if a drive transistor on this circuit were to short, the 1A fuse will blow before more damage occurs. Also, the pinball will remain mostly playable, except for that Jet bumper, or slingshot
Each fuse has an LED indicator. With a ground wire attached, the SSB will show which fuses are good.
