I have a Dr. Dude which shows this problem - I put LEDs in the Playfield inserts a while back only to discover that they were essentially always on. So I took them all out again and the game is fine - except for the lit lights in the Dude-o-meter which have sort of a slow pulse which actually looks kind of cool (like a smoldering fire), but probably not intended.
I figure it has something to do with cyclical signal sent to the lamps and that leds react faster. I did some rudimentary Transistor Checks on the lamp matrix, but saw no indication of an issue. Since the issue was on most of the inserts I figured it had something to do with the unit generating the pulse driving the transistors (I think the only LEDs I could leave in the game were those under the mixmaster flasher domes - I don‘t mean the flashers though, but maybe I need to check this).
Any suggestions, tips, easy solutions (or hard ones) ?