Don, your faulty I/O boards very likely will have a cooked mosfet or 2, caused by and up or downstream fault.
There are 8x 100v N channel's on each I/O board for driving coils, 4 each side.
Pic shows 'em. I can't read the part number on them but the Great Per has ID'd them as PSMN039-100Y
*ESD controls apply*
Test 'em with your meter to confirm which are faulty. Connector pins are labelled so if you don't know the coil number, buzz 'em out.
They cost all of 2 bob each and take 2 minutes to replace with the rework station.
If the fault still exists up or down stream, the I/O boards will fail again. Those power boards are junk. Not at all fit for a hot, high stress environment. A bit of PCB lacquer is helpful but they need to be cleaned, with the risk of tracks, pads, and land, just falling off.
There are also 2 big P channels acting as switches. One for 12v and one for 70v. You can check the test points, or confirm the 70v & 12v led's are on before getting out the meter for these as I've not yet seen a failed one.ft_io_70v (resized).pngft_io_swv (resized).jpgft_mosfet_100v_3 (resized).jpg
Pic shows 'em, again I can't read the part number, but the Great Per says FQB22P10.