I just read through this thread quickly but don't recall seeing this mentioned - maybe you have the hold coil and the power coil reversed at the lugs. Take a photo of your coils as installed on your CFTBL, then measure the voltages on the 3 terminals of the coil with the flipper energized and let us know what the voltage on each terminal is with respect to the terminals shown in your photo.

This almost has to be the problem - it's the only way the game could be playable with a known good fliptronics board and still have coils overheating.

Sorry...that looks correct. I'll re-read the thread and see if I can find something we've missed...

Based on what you've said you swapped, I only see two remaining scenarios:
1) CFTBL coils just get hot under normal operation, or
2) Your wiring harness is incorrectly swapping hold and power coils. That's very unlikely, but you can check the wires on J907 and J902 and make sure the colors match the schematic below.

But if the left and right coils are behaving identically...maybe the heat's just normal? Would still be interested in the coil voltages when the flippers off and energized. Also you could remove J902 and measure the resistance between the top (common) winding and the power and hold terminals. To eliminate any possible effects from the diodes, measure the resistance one way, then reverse the ohmmeter leads and measure it again. If the readings are different (they may or may not be depending on your ohmmeter's characteristics), the higher reading is the correct one.

right_coil.jpg

And ultimately you found the root cause to be the transformer? I've seen lots of unexpected things in electronics, so I can't say that's impossible, but it's hard to understand how a failing/bad transformer could cause a coil to overheat. I guess if there were somehow shorts in the primary making the number of effective windings lower, the output voltages would be higher. I'm very interested in this because I love an (electronic) mystery, and this certainly seems to be that.

It is interesting that my AFM has plenty of power for that light lock shot, but my HS2 only barely makes it around the back and up the ramp to lock a ball. They both use the same coil and have rebuilt flippers. I don't think it's a coil heating issue (it has the problem when I power on), but thanks for reminding me to revisit it! I need to check the power supply under load...