A
Crank index is another one that most forget to mention or check-if she's twisted out of phase you'll pull your hair out trying to find the problem elsewhere. All you need is a degree wheel,dial indicator and 5 minutes of your time.
Had this happen to my daughters RMK500, it was a pain to figure out. It popped once after running perfect all day and then wouldn't run for schmitt. Good call FTX