If the flipper was working well and has just stopped working properly, without any work being done on the game, like the flipper coil being replaced etc, then follow these steps....
Yes, as previously mentioned, the first thing to do is test for 50V at the flipper coil. On the Upper right flipper, put the red lead of your multimeter on the BLUE/YELLOW wire that is connected to the coil (and your black lead on ground, any metal grounded rail in your game), you should read >50V DC. If you do, then the power train or power wiring to the coil is ok.
There is a quick way to check if the power coming to the coil, the coil and the assembly is in good working order. Go into the back box to the IO Power Driver Board and disconnect the plug at position J9. Then grab a test lead with an alligator clip on each and connect one end to a metal/grounded point in the game. With the game on (most likely with a game started and the playfield in the up positon) momentarily touch the other end of the test lead on the BLUE/BLACK wire connected at the flipper coil. If the flipper flips, strong snap action as it should, then the fault most likely lies on the IO Power Driver Board. I'd then look at replacing Q14 and see if that makes any difference. The circuit is shown on Page 106 of the manual.
