So, I have some interesting news on the 160V drive. I've moved to a test bench that has only a 12VDC supply and an encoder being hooked up to the drive. I pulled the heatsink off the drive and probed the differential receiver while turning the encoder. Interestingly, *neither* input is toggling (although I can see the toggling on the EXT pass-thru connector. So, either whatever is between the connector and the 26C32 receiver is bad or the receiver itself is sinking the input. This is the next area of investigation but it is absolutely the reason that the amp is not recognizing any turning of the encoder. And that is progress.

Of course, all of this begs the question of *how* the current state came about. There is no visible damage to the board or its components. No Char Broilers there, or even crispy looking stuff. Strange. The other good news is that the manufacturer is in contact with me now so I'm hoping we can resolve the (apparent) noise issues on the 80V drives. Fingers crossed.