Old PRT 32 x 24 Shopbot from the 90's

[TNWALKINGHORSE]

Hello, recently my z-zero plate stopped working. When I measured the voltage at the PC power supply connector to the PRT board, it is showing 5v on 1st pin, then 2 grounds and 12v on forth pin. However the pin 1 that the z-zero plate is connected to, on the main board, is only showing 1.1v. So my e-stop and my z-zero are not working. Any one ever had this happen? If there any surface mounted fuses or other components that I can check? Thanks!

[TNWALKINGHORSE]

UPDATE: So I moved the z-zero wire to pin 3 which had 5 volts. I changed the settings in my variables file to look for input 3 instead of input 1, and now it is working fine. However, I am still not sure what controls the 5 volts on pin 1. And why I am only getting 1.1v? Does anyone have the schematics for the PRT 90902. I believe it is verson 3.41 board. I would love to see what IC controls this and repair it. It this port blows, I am screwed. Thanks!

[coryatjohn]

You could use one of these instead of the plate:

34701

https://www.ebay.com/itm/121895800409?epid=1558296311&hash=item1c618e4e59:g:JPoAAOSwB4NWzMUq