Having issue with this old Miprom 21. Has been modded to an AC machine, using a HPV-900 drive. Do not know how long ago it was modded to this setup.

My issue is that on my analog direction inputs on drive I am only getting positive VDC in both directions. I saw that the input was being fed by the maroon plug on bottom right of my relay pilot board.

I switched out the relay pilot board being hopeful that was my issue. No dice. I guess my main question, is which board has the logic to tell the voltage to swap polarity in the down direction? MSU, CPU, PIO?

Customer is on an outage right now in a power plant and they NEED this freight elevator so you can assume how much pressure is being put out to "just get it going"