Need Help!- MAZAK QT8N stopped with Alarm 039

[ua6lfj]

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.

ua6lfj

[Karsue]

Hi ua6lfj,
I know that it has been long time that you posted your question but I am wondering if you solved your problem.
I have got the same problem on my machine (Alarm: 39 OVER APMERE).
If you or any one else have any recommendation, please help me with this.
Thanks.
Karsue

[ua6lfj]

Hi Karsue,

Unfortunately, no good news so far, machine is still dead. As stated in my post first suspicion was the motor (unbalanced winding inductance). We have contacted Chuck Nichols @ Endeavor Technologies, Inc. 630.562.0300 Endeavor Technologies Spindle and Servo Remanufacturing Excellence who is ready to rewind the motor for approx U$3K however we still have doubts in motor failure. Still trying to find problems in servo controller ourselves.

As you have similar problem I would suggest you to perform simple measurements that would probably help us both to eliminate at least some uncertainty: If you have access to LCR bridge meter, please disconnect machine from mains and open electric box cover located on the main spindle motor (at the back bottom of the machine), then disconnect all three phase thick wires (marked WU, WV and VU that come from inside the motor) and measure inductance between them at 10kHz signal (very important to make sure the frequency is 10kHz as readings on other freq will differ) and compare with ours:

Readings @10Kc

WU - ESR=24.30 Ohms L=1039uH
WV - ESR=20.01 Ohms L=965uH
VU - ESR=24.32 Ohms L=1039uH

Note our WV is 7% less inductance to other two windings, which is, according to Chuck could be an indication of short turns in WV as allowed tolerance should not exceed 2%. Also, he suggested to measure resistance to DC current, which should be strictly 0.063 ohms for all coils, but taking this measurement requires special milliohmmeter working on high current (regular testers cannot provide accuracy in such low values measurements).

If your motor have identical inductance 1039uH and you still have 039, the problem is definetely not in the motor. Please let me know your results.

Br

george@stealth.ae

[Karsue]

Hi ua6lfj,
First of all thank you for your quick reply and then I have found the problem 2 days ago (exactly after I post the thread) the problem was on servo axis amplifier and one of IGBT transistor (6DI75A-050) was blown.
I think you should check the IGBT on your servo axis amplifier and compare it with each other with multimeter.
If you think this problem is on the spindle then check servo spindle amp. (FREQL) but I think it is because of your servo axis drive amplifier IGBT.
If you have any questation, do not hesitate to contact me.
Karsue