After replacing several bulbs and fixing left flipper (blown fuse) I lowered the PF and powered on to start testing remaining coils. While getting about three tests in, smoke is wafting up through back of PF. I killed power. Made sure I didn’t cause a short somehow, nothing found. So I decided to power back on. No more smoke coming. In further testing now Coils 37-40 will lot fire in test mode. Raised PF again and looked at those coils. Found a burnt coil #39 with 3 wires (violet green) including a thinner one the tieback as I have learned. I perform continuity on all wires working backward from the 4 coils that have that color pairing. Both the thinner tieback as well as the larger wires all continuity check back to their respective board locations including the Orange-white for coil #39.

The coil is burnt and locked for sure. When I was tracing wires back to J107 for testing I noticed seemingly unrelated F103 was blown.

It wasn’t blown before I saw smoke because I checked all fuses after fixing the left flipper due to a fuse.

So is there anyway F103 has anything to do with those four coils not working?

I pulled the 8 driver PCB. I have never replaced transistors before and I understand I should also change the pre driver ones as well.

Do you think I need to take the driver board and remove the TIP102 transistors and test them out of circuit? Can they be tested in circuit?

What caused the coil to burn? Can the root cause be the transistor? I thought usually they burn because of something else going wrong.

What order of testing steps should I take now?

I took a long time off from pinball due to health issues (4 surgeries) that spanned several years. Now I am healthy and want to play my pins now.

Thanks for any good advice in advance,
-Nac

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I thought that's what I would find. The tieback is still intact and tested even moving the wire around trying to see if the joint cracked. It test out fine and all the way back to the connector. What I don't know is if the connector itself has an issue. I checked the corresponding TIP102 for coil 39 and it is messed up. All of the TIP102's register .4-.6 volts when tested except coil 39 TIP102. one side registers .58 and the other .04. I also checked the predrivers, and they all test fine. SO I agree, somehow the tieback seems to have been interrupted but not in test now. I plan on replacing the connectors before firing up. I bought a spare driver 8 board as well. I will do the tieback mod in the backbox as well. Am I missing anything?

I actually posted in General Tech and it was moved here, so my bad. Can I get a mod to move it again to the STTNG owners club?