I am having this same problem on my TSPP. I checked the End of Stroke (EOS) switches and they are functioning perfectly. The lights dim in the back glass more noticeably than in the playfield with the right flipper button more than the left. Now there are 3 flippers on the right in TSPP and 2 on the left so possibly the increased dimming is related in that way.
My flipper coils look good and I see no melting though I'm not sure how to check them fully, what should I do?
How can I check for a bad ground?
@Flyer666, did you fix your problem?
I see a lot of people online just living with this problem but I'm afraid that will lead to something more serious breaking.