miprom 21 vp13 fault

have a unit that is faulting out on a vp13, motor field feedback fault. started a couple months ago, route guy reset, and it ran another month, another reset, now it is starting to do it once a week or so. i reseated connections in drive for the motor field circuits, checked connections to mf, also checked reference current with feedback current, and while i was there, they were right on. sure its coming back, just wanted to get your ideas on what to replace first, feedback board ? etc, just wondering if anyone has had this before. thanks

Usually this is caused by the field firing board. It is behind the field feedback board. It has 4 120 ohm resisters, 2 per side in parallel. these should measure around 60 to 65 ohms. they get hot and start flaking out.

thanks john, thats where i will start.