View Full Version : bally SS solenoid driver board + expander

6th August 2009, 08:08 PM
Had a problem with medusa outhole kicker - intermittent . probably a dodgy connector but examination revealed incorrect coil so I thought I'd change it for the right one. simple exercise right? no. here's what I learned.

Bally SS machines after EBD had solenoid expander boards attached under the playfield to increase the amount of usable solenoids on the game. most ppl know that a coil is driven by making a ground connection and there is always power at the coil, so in effect a solenoid is fired by a driver board TIP102 transistor creating a path to ground.

the expander board is a relay that is driven by a flashlamp SCR driver. it allows the one TIP102 to control 2 coils - they usually choose coils that aren't used much like the outhole kicker and target resets.

it would be a fair assumption that the expander board switches ground (because that's how coils are driven) right? wrong! it switches coil power so that assumption cost me a TIP102 and 330k resistor on the driver board.

the things not stated at pinrepair are:

the expander board switches coil power and 2 diodes (4004's) are required on the coil being driven - one across the lugs with the band to the power (expander board wire side) and the other in series with the power line (expander board wire) with the band towards the lug.

working fine now but that's a handy one to know, it didn't help that I didn't have schematics (the EBD schematics helped me figure it out).

6th August 2009, 08:25 PM
Pinball machines seem to be one of those things where you can't assume too much unfortunately! No diagrams makes it even harder. :(