Howdy, I picked up a STTNG this week and it needs a little bit of work before I can play it. This is my first dive into repairing WPC so I have been doing a lot of research on pinball ninja and asking lots of questions to my local pin heads. I have what at first sounds like an age old issue with STTNG but after digging in for a few days, appears to be something not so simple.
The two under playfield diverters and the top drop up and the top drop down coils do not fire. This of course causes the balls to be sent looping around the machine as it attempts to lock them into place before a game but can't. The rest of the coils fire fine during Solenoid testing, its just these 4 coils with the issue (yes I am looking at you Mr Aux 8 Driver Board).
So armed with the issue I went and found a slew of reasons that cause these four coils from firing. Here is what I have verified so far:
- The coils fire when the tabs on their transistors are grounded
- Fuses on main power board test out well (I even replaced F103 for good measure)
- I removed the aux driver board and verified all 8 transistors are good (one leg tested ~550 and the other at around 650, the middle around 3)
- All four of these coils look good, not fried, and they obviously fire (see first bullet point)
- The tieback wire appears connected to the correct coil (the bottom green one for the top drop)
- All four coils, when testing for volts, are testing around 71
- All four coils, when testing for resistance, are testing between 6 and 13
- All connectors on the aux driver board appear to be seated well and there is nothing burnt
- All connectors on the main driver board and the aux driver board have been re-seated
Couple of other items of note:
- Had a shorted BR1 on driver board that I replaced and that fixed a lot of issues.
- There was crispy connector for the GI in the head with bad hack in place. I re-pinned the bad pins and made new connector. GI for head is still out but I suspect myself and will revisit when the coil issue is figured out.
- The right gun motor has broken short crank arm
- I have tested most if not all the fuses by now and replaced a few
- This is a re-import that has been working fine for more then a decade, but was originally from Germany I believe
What other tests can I run to isolate where this issue is coming from?