Can anyone help in troubleshooting our Mazak Quick Turn 8N lathe?

Machine is equipped with Mazatrol T32-2 (Mitsubishi) CNC control and Mitsubishi Freqrol FR-SF-2-7.5KP-BC AC Spindle Controller.

During past several months machine could suddenly stop in middle of work with Alarm 039 (OVER AMPERE), which could be restarted. O39 states for " An excessive current has flown from the plus side of the DC bus bar. A ground leak or a short-circuit has occurred in the motor power line, or an overcurrent has flown through the servo amplifier circuit for a predetermined time or more". Sugestions given in the manual are to check for ground leak, short circuit, whether speed detector is mounted in "STY" direction, replace RF01 card, speed detector (where are all these?), check for malfunctions in the main circuit. Tighteening spindle motor belts seemed helped for somewhile, however recently machine stopped completely consistent with 039 right after energizing CNC. The LED on FR-SF shows "E7" stating for external emergency stop given by the CNC.

Motor was disconnected and checked for short - all three coils were measured with approx 0.07ohms. As we have no milliohmmeter we checked windings for inductance (by bridge at 10kHz signal) resulted in identical two coils measured 1035uH and one 975uH, which is sensitively lesser than other two and more than allowed 2% tolerance.

Motor was under suspicion untill we attempted to start machine with motor completely disconnected. The CNC came up with same 039 Alarm code. Now we suspect solid state switching modules in the FR-SF.

Did any one have similar problems?

Thanks in advance for any help.

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