Need help on Servo Dynamics board SDFP1525-17

[Twil759]

I am trying to get some help on fixing one of our servo boards for our Hurco mill. This has been a frustrating ordeal that has had our mill down for 2 months. I am not that experienced with electrical. We have sent the board to Servo Dynamics twice. The first time they repaired it. Then we ran an order of 50 parts. The next time I went to tool up, there was a problem again on the board. We sent it back to Servo Dynamics and they said they tested it and couldn't find a problem. We got it back and it still wasn't working. The original LED that was coming on was the RMS light. They supposedly fixed that. The second time was the SUR light. The error that shows on the screen says "Servo error - Loss of feedback." I have had numerous conversations with a tech at Servo Dynamics and I don't find him all that helpful. He told me that we had a problem with the transistors, so we changed those and it still isn't working. Does anyone have any advice or a manual that they would be willing to share? I am looking for a solution and trying to save money at the same time... Please email me at twilson@ymsinc.net if you can help. Thank you...