Need help with edm problem diagnosis - Hitachi 345Q

[genestapp]

The machine is a 1991 Hitachi 345Q 5 axis wire edm. The controller is an H-MARK-100 using MARK100 V 2.43 software. The machine has two pulse counter circuit boards. The reason for this is because one of the pulse counter boards controls X,Y,U &V and the other controls Z. The pulse counter board which controls the X,Y,U & V has a red LED lit which indicates that the encoder or linear scale circuit wiring is broken according to the maintenance manual. This is triggering a 403 alarm in the software which is an encoder error on the X axis.

The power going to the machine is coming from a step down transformer (460v-230V). This has been checked along with the phase direction. Everything seems ok as far the current. The machine has worked very well except for the occasional 403 error. At one time, I could simply turn the machine off and turn it back on a few minutes later to clear the error and everything would be fine.

It has gotten progressively got worse and now I'm plagued with the constant 403 and the respective red LED on the encoder's pulse counter circuit board. We did have the pulse counter board checked out and everything seemed ok. I have also swapped the pulse counter boards and jumpers in which the red light would appear on the other pulse counter board. At this point we've ruled out bad circuitry within the board itself.
Had a specialist come in and check out the pulse counter board. He also re-tinned the contacts and took some sandpaper to the slots on the main board. Then he checked the cabling to the encoder for continuity. Again nothing wrong was found.

I'll attach photos shortly as I have to edit them to a smaller file size

Does anyone have any suggestions on what could be wrong or know where I can pick up a h-mark 100 controller for this Hitachi EDM?

[Medm]

It seems to me that you have a bad encoder.

Corrosion builds up over time on the encoder reference mirror and this seems to be the problem in this case. If you have a mechanic you could try switching the encoder from another axis. If the error indicated after the switch moves to the axis of the encoders' origin, you have a bad encoder.

[genestapp]

I'm going to be working on fixing it some next week. These older machines are just so complex. I think I've narrowed the problem down to an employee painting the machine haphazardly and getting paint where he shouldn't have. I'll have to take it apart and clean some stuff