I have a Yeong Chin Supermax (Bridgeport clone) circa 1989. It has servo dynamics motors and amps ( SDF-1525-12).

Lately the X axis VOL LED is tripping frequently. Otherwise the axis is running normal and turning it by hand has normal resistance.

I have a manual for the amps which says that nuisance tripping of the voltage LED may indicate the that the shunt regulator fuse may be blown. It also says that the shunt regulator fuses are optional. My manual doesn't indicate where these fuses are located. Are they on the amp board or on the chassis? Is there one per amplifier or shared? How do I know if I have them and how do I test?

If that isn't the problem, what else might be the issue?