I have a High Speed that works fine most of the time, but occasionally will freeze in the middle of a game with GI lights and music still playing but no power to the coils. I have done some research here and see that it might be a coil diode issue on a flipper coil. I took a closer look at my game and see that the upper flipper (which has always been kind of weak) has no diode on the coil. All of the flipper coils in this game are supposed to be the same, and are FL 23/600-30/2600-50VDC. I thought that the missing diode might be the problem so I soldered one in. When I went to try it out, the upper flipper seemed stronger, but the hideouts immediately stopped kicking out. I investigated and found a 2.5 amp slow-blow fuse in the bottom of the head had blown. I cut the diode, replaced the fuse, and everything seems to be working fine now (except back to the weaker coil). I'm assuming that there is supposed to be a diode on that coil, any ideas on what might be happening?

Thanks for the reply. Everything stops working when the machine freezes. The background music plays, GI is still lit, but switches and coils stop responding. The ball drains and the background music just plays in a loop. It's similar to this situation:

https://pinside.com/pinball/forum/topic/high-speed-intermittent-lockup#post-5294261

If I turn off/on then everything works normally again. I tested the voltages coming out of the power supply board and they looked good (4.95 volts).

No I don't think so. I was considering doing this as my next step. Could this be the issue even though the voltage check out okay? Might the voltage be dropping later during play?