System 9 - Locked-on Coil

[ibis]

Got a System 9 game and the left kicker is locking on.

Tested the coil, reading 4.2ohm
Tested the diode, reading good
Tested the driver, reading good
Wires are located on the correct lugs

Whats interesting is, it worked before taking the PF out.  Only has 4 plugs so theres nothing to mess up.  Secondly, the driver has been replaced before, its actually circled in the manual so this is something that has happened before.  Unsoldered the wire to set everything else and everything boots, coils fire, switches are all good, lights are solid.  Any ideas?  It's probably something dumb, just cant see it.

[FUNWIZ]

Well we don’t know what game it is… Turn the game on, if the coil immediately fires, undo one of the four plugs, unplugging it. Still firing? Unplug another one.  When you find the one that’s powering the coil lightly tap it to the connector, should spark only that one pin, and follow it back to the transistor.  If it’s the same transistor that was circled, then maybe the pre-driver is bad.  Maybe it got accidentally smashed and the wires are touching on the leads to the board? 

[ibis]

Its a Williams Sorcerer

[FUNWIZ]

OK there’s two ways of doing this. First way is replace U6 which is a 7402, replace Q74 2N4401, replace Q75 TIP122.  Second way is swap pins at 1J18-5 with 1J18-9 and also swap pins 1J19-7 with 1J19-9. This uses up the spare driver circuit not being used and saves time replacing the other parts. You should mark the cabling that this was done for future reference if it’s left this way. You can always use the spare parts in the other circuit, Q84 and Q85.

[ibis]

Started checking for a ground short on J18 and J19.  Turned out J18-5(orange/Brown) was grounded but it was playfield related, not output related.  So I looked more closely at the stand-up switch and found the short there!  Sometimes you need to get close to see the gremlin! LOL!!  Thanks all, another game 100% working!

[FUNWIZ]

Glad you didn’t have to tear the board out of the game and do all that work to it. That was an easy breezy fix after all. And you were right it was in the playfield area.

[ibis]

For sure, I always play test games before tearing them down and I knew that kicker was working!  9 out of 10 times its something thats so simple you just dont see it, I always think the worst lol.

[k7]

it's a williams. your LUCKY when it's simple.

our black knight just decided..."nah, i ain't gonna start a game today"

no reason.       give me a as-2518 bally anyday