Got a call to look at a Stern Nascar pinball machine that had an error of “Looking for Pinball Please Wait” when the game turned on. Game had all four balls but was not kicking over to the trough. I looked for any broken wires on the Ball Exit Popper coil and didn’t see any. I tested the voltage on the coil, and it was present. I grounded the non-banded side of the diode and the coil fire, which proves the coil was fine. I also noticed that bracket was starting to break. It didn’t take too much more before the coil stop broke off of the bracket.
Took the assembly out of the game and took the bracket to a local medal shop. They were able to weld it back together. It’s stronger now than when it was probably new.
I tried to fire the coil from the test point (TPL1 FET) to the white side of resistor R7 and did not fire. I tried a couple next to it, and they all fired. I took the CPU board out and replaced Q7 with a IRL540N. Tested the game and the coil is now firing like it should.
NOTE: I made a mistake and bought the IRL540N off of eBay and turned out to be a counterfeit part. When I used this transistor it locked on the coil and blew F21. I spent some time on this problem and would have saved myself a lot of time just buying from a reputable dealer. You can see a circuit breaker in one of the photos.
I noticed one more problem well testing the game out. The ball would drain and about 1 out of ever 5 drains would not register. I took out the trough opto boards and cleaned and resoldered the header pins. This fixed the issue.
Funny how one small part can totally disable a pinball from working.
Game is up and running again!