Mitsubishi Meldas LOB Servo OCP alarm

[Whiteforest]

Hi guys,

I'm usually on PM forum since I don't know heaps about CNC controls. I've run 2 machines since starting a small jobbing shop a couple of years ago, and always dreaded the enievitable day when a control would go. I posted this over there and I thought I would try my luck here.

2 years in business and I have my first attack of the NC control blues. My ageing Mazak QT8, mazatrol EIA-T (Meldas LOB)has a problem with the Z axis servo amp (TRS-050) erroring out . this started intermittantly some months ago, but a restart would sent me on my way, good for days, eventually hours and now, at times, seconds, other times hours.

I have the manual and it tells me I have an OCP (over current protection) alarm. I should state that I have only a rudamentary knowledge of electronics (enough to be dangerous) but have a friend who knows some about servos. We pulled the module and friend checked resistance on the power transistors, we even heated up the heat sink to try to simulate working temp, but they looked fine. Bear in mind that this module will still work for hours at a time.

Next we reinstalled amp and checked voltage between check pins CHA and CHB (OCP input, OCP ground) which should read .03 mV per amp servo draw. Axis X Volts was minimal. Z would waver anywhere between .3 and .9 mV with associated hum from servo, before tripping out with no discernable spike in the reading (cheap digital multimeter). Servo was cold to the touch.

I guess my thinking is that I would like some advice as to where to go from here, specifically does it sound like

1 a tuning problem- call a tech

2 a transistor problem - how can I diagnose that for sure?

3 an encoder problem?- as above

4 a logic problem- buy a replacement board?

My friend has just left town for a few days. My only tools are a multimeter and desire not to break the bank.
Any help appreciated

Vincent

[A1CNC]

Hi Vincent,
I Have 2 leadwell's that use the trs 50b drives. I had a similar problems with one of my drives. I tried tuning the drive, I checked the transistors. I finally sent just the top card in to mitsubishi USA and they rebuilt it for ~$500.

Since Getting the card back I haven't had a problem. Knock on wood!

Eric

[Whiteforest]

Hi Eric,

Thanks for the reply. It doesn't look good

[A1CNC]

Hi Vincent,
Just thought of this,
Did you try swapping the drive to the other axis to see if the problem follows the drive? It is possible it could be the cable or the motor.

Good luck,
Eric