Spindle driver/inverter on Milltronics Partner mill not working

[desert_rw]

Hi;
This is my first post to this forum, I have come here searching for suggestions that will lead to a solution for my Milltronics Partner CNC mill. It looks like this is a great community for people with similar interests and skills.
Basically, I have an older (circa 1995) Milltronics “Partner” 3 axis CNC mill that I purchased after refurbishing about 5 years ago. I don’t use the mill a lot and it has run great, always doing a good, accurate job despite my learning curve and mistakes. One of the best features of my rebuilt system has been the absolutely quiet spindle bearings. However, the spindle drive system is now my basic problem.
Whenever I command the spindle to run (example: M3 S2500) it barely moves then the machine enters “E-stop” mode. When I look in the back electrical cabinet I see the Saftronics PC3 variable frequency inverter/drive displaying “Oc”- this indicates “Overcurrent”. The booklet for the inverter claims this is due to 180% of the rated current being drawn. This symptom started soon after I tried to do some rigid tapping thru some ¾ steel plate with a 5/8 tap- the machine did not have enough torque at the slow tapping speed to make it. Basically when I tried the big rigid tapping job the spindle shut down immediately when it reached max torque (current). But now it immediately and almost always goes to “overcurrent” mode when simply starting the spindle under no load at all! I’ve manually checked the spindle and bearings, they are very free turning.
I have jumpered around the “safety loop” at the inverter, the machine no longer enters “E-Stop” mode but the spindle still stops immediately and the Saftronics displays “Oc”- this proves the source of the “E Stop” is the Saftronics inverter. I have also taken the Saftronics PC3 inverter out of the machine (apparently originally made by Yaskawa) and disassembled it completely looking for burned current sensing resistor or anything else odd. Nothing was noted, I cleaned it and re-assembled, installed the wires, and the symptom is still identical (at least I didn’t screw anything up).

When I searched online for this inverter I found that it is no longer made or supported, but I also found that there are at least a dozen variations on this particular inverter from Saftronics (Yaskawa). I’d buy one of the similar inverters on Ebay but I also cannot confirm the ID/model of my inverter (I suspect the original model no was removed by Milltronics). It uses 208 VAC three phase input, and the following markings are inside the unit:
MEC-37AV-0 (on main PCB)
Lot no N4W0005-004-144 (on main PCB)
YPCT31143-1A (on main PCB)
Code no ETP608270 (on main PCB)
SN 129617 (on alum case)
Any suggestions for repair, schematics, replacement (at reasonable cost), etc would be much appreciated. I also don’t know if there is a programming parameter in either the inverter or Milltronics system that needs to be reset, I’ve looked at the programming gobbledygook from Saftronics and it does not make any sense yet.
Apparently there is also a Saftronics PC7 that was intended as a replacement for the PC3- but I’m not sure about the installation changes, programming, etc.
Any thoughts? Ideas? Parts? I would like to use this machine lots more!
Thanks in advance!

[bocko912]

My partner 1D VFD was replaced with a Yaskawa V1000. It works well the only problem that I have is that the spindle will not orient for my tool changer. Other than that no problems.

[jpawelk]

Try to remove the output wires (the 3 wires that goto the spindle motor) and then try and run your spindle. Of course the spindle will not come on due to the removal of the wires. If the drive still displays the OC, then the drive will need repair or replacement. If the alarm does not show, then there is a problem with your spindle motor.

[desert_rw]

JPAWelk;
Thanks for the suggestion- I will try it. I'm reasonably convinced that the motor is OK but you are right- it could be internally shorted and drawing too much current even though it turns freely. That would seem to be a pretty rare failure mode for high end 3 phase motors but still possible.
Thank you