Hurco KM3P Servo Amplifier Fault "BIE"

My 1987 KM3P has been a workhorse in my small home shop for the past 14 years, but recently it has been having an issue with the Randtronics servo amplifier not powering on correctly; On the Fault Logic Board, the BIE fault LED is on (see photo).

In the owner's manual (section 5.5.7) it says the cause is: "The bias error indication operates if the sum of the plus and minus 12v supplies falls below 22 volts. Peak output current on each bias supply is approximately 2 amperes. However, if either supply is overloaded, it decreases significantly because of the holdback capability. Also, the plus supply tracks the minus supply. The most common bias error fault occurs because one of the supplies is shorted to ground"
The corrective action is: The drive should be reset and retried after external ±12 volt bias loads are removed".

How/where do I locate these ±12 volt bias loads ???

Thanks in advance,
-Mark

If I remember correctly, there is a fault on the Fault Logic PCB. Check the fuses and the voltages that are supplied by the little transformer on the servo chassis.

Thanks Bloke!

I checked the transformer and (guessing here as I don't have a schematic for it) measured 117V across the primaries and ~19.6V across each of the secondaries.
The fuses (2 of them) on the Fault Logic Board both have continuity.

Where do I go from here?
-Mark

I've removed the Fault Logic board and all three of the axis drive boards. I can't find any obvious problems. In addition the transformer on the servo chassis appears to be funcioining correctly.

I'm still get the BIE error LED, even when the axis drive boards are disconnected. Is my only option to repair/replace the Fault Logic board?

Anything else I should be looking for?

Bloke? Anybody?

Thanks,
-Mark

Good news... I purchased a Fault Logic board on Ebay, plugged it in and the servo drives powered right up. Huzzah!

Is there anybody who might be able to diagnose and repair the old board so I can have a backup?

-Mark