I have a problem with my (Bally) Attack From Mars machine. I tested and switched a lot of parts and still can't solve it..
so I hope some experienced techs still have some ideas because I'm losing my confidence / patience..
In the past I had shorted coil power onto the switch matrix 
The game now has a pinled cpu board and aftermarket security rom from someone in France installed.
Because of all these non-original parts I start to doubt everything.
Rom version is 1.13B in case it would matter (yes I doubt everything now).
The problem is that the scoop coil does not always work. Balls get stuck in the scoop.
You hear the coil buzzing, but the coil doesn't seem to have enough power to kick out the pinball.
What I did:
1. replace the coil, check whole mechanism (plunger, coil sleeve, ..)
This did not solve the issue. Mechanism looks ok, plunger is ok (not broken,..), return spring is ok, coil sleeve ok, ..
Issue remained, sometimes it kicks, sometimes it doesn't.
I noticed (then and now) that the isssue happens more when the playfield is in the down position than when it is up.
When I raise the playfield to look at the mechanism, the coil can fire 10 times correct in the coil test, I lower the playfield back in the cabinet and it just buzzes..
Also during gameplay when the ball is stuck in the scoop, it often comes out during a ball search (when the martians are active).
For a while it worked better if the drop target bank was up - I noticed that during play when the bank was up the scoop would kick out well, when it was down the scoop more often had the issue, and then during ball search when the target bank moves up it would kick out the ball.
But this is still random - today it just fails often, and target bank doesn't seem to make a difference.. I can't always replicate the issue.
That made me think there was a bad connection somewhere.
2. There's a connector between the coil and wiring loom. Replaced this - no solution.
3. Replaced the wires between the coil and the connector - no solution.
4. Noticed other coils did not seem to have the issue, they all work correct, so I suspected a cable broken in the wire that drives it - purple yellow if I remember correct.
I replace this completely from the coil until the idc connector in the backbox - no solution.
5. Took out the driver board, noticed that the transistors for this specific coil had been replaced in the past.
Replaced the Tip102 and Tip36C transistors. - no solution.
6. Replace the driverboard with the driverboard out of another machine - no solution.
7. replaced the pinled cpu with an original bally cpu out of another machine (I did not have to switch the asic so that can now als be ruled out as cause) - no solution.
8. replaced the flatcable between cpu and driverboard - no solution.
So.. now I'm really stuck.
I replaced everything from the coil until the cpu. Issue remains.
The only part left is the red wire (power to the coil) but that's 2 wires, goes to other coils, and as no other coils on the machine seem to have the issue I don't suspect this.
As raising the playfield helps solve the problem - my machine has a larger subwoofer in the cabinet. It has a bigger magnet but it's still a few inches away from the coil, I would find it weird that this has influence ? Could it ??
Any ideas what can cause this problem or what to test / replace next ?
Fort Collins, CO
