Need Help!- mitsubishi diarol drive malfunction

[hfk]

Last november I bought an old (begin 80's) mazak VMC with a fanuc 6mb controller. With lots of info from this forum I got it to work, and made some parts but recently the problems started.

The spindle motor is a 5.5 kw dc (mitsubishi SDN-CFZ 112l fr) motor controlled by a Mitsubishi Diarol SDZ 2F F drive. Feedback is with a tacho generator and oriented stop by a magentic sensor.

Sometimes at a tool change the spindle drive kicked out while orienting with a 'field loss' error. It mostly happened when I was playing in MDI mode. Powering off and on the drive solved the problem. This was a problem I could survive.

Later the spindle made a humming (alike 50 hz) noise when stopped during toolchanges. Like some rectifier bridge was broken. Speed control was not stable without load. The same day I still made some parts, because after some time the speed trouble disappeared and I needed only one tool so I didn't need the tool change.

Next day the trouble really started.
The machine/drive didn't start any more. Drive gave me the 'field loss' indication at powering up. Even a 75 amp input fuse blew and other error lights came up. When I put a clamp meter to measure field current I measured a 15 amps at 60 volts in the field. I thought the field current measurement was defective.
Trying a lot of options (restarting, rotating the spindle, checking the brushes etc) I blew a fuse from the shop and a protecting varistor in the cabinet, but didn't make any progress.

Because of the moist conditions I put a electric heater in the cabinet. It is a big shop without heating. In december it froze but all worked properly. With the temperatures rising again everything became more moist then ever before.
Now the controller still gives the field loss error, but puts a 3 amps through the field, which is base current for the motor. It also gives a tacho loss error while also the 'up to speed' led lights.

Does anyone have any idea where to find and solve the problem? I have the manuals but my electronic skills are not so good. Straight electric an mechanic is no problem.

[canelca]

We had a similar problem recently with this type of drive. After a long weekend and with the temparature a lot colder than some weeks ago the drive issued this FIELD LOSS alarm. We tried clening up the brushes, checked motor, compared the motor test with another similar units and the alarm kept coming on. Suddenly it began to diminish until dissapear. Looking in the book I found that when the alarm occurs you have to check 501 LED: it was off. I undertood that the front board was faulty and called MITSUBISHI. They told me this could be an issue or the built in power supply. Another option is trying to disconnect the FIELD EFFICIENCY circuit by disabling a diode. By now the alarm is gone. We have noticed that this happened before in similar situations: long weekends with colder weather. Our plan is bring a MITSUBISHI tech to check all these DIAROL drives because they are really old: more that 20 yrs, beyond the life span for any electronic component.
Carlos C

[canelca]

We finally found out: the tachometer on top of the motor was damaged and causing this field loss larm. Other symptoms were: unstable motor load on gage, noisy spindle, a couple of times tach loss alarm. We replace the tach and all these symptoms gone,
Good luck,
Carlos Carias.

[hfk]

maybe a solution to other people with the same problem.

my drive turned to be really damaged. Few power components blown etc. I was happy the company repaired the drive under a 'fixed price & no cure no pay' condition, because I had to send him in twice and all together it took several months.

I still blew the mains fuses of our shop at moisty weather. The problem seemed to be in the spindle drive (phase sequence didn't light etc.).

my solution:

I put an electric 500W heater with a timer under the drive. Before I start up, I turn on the heater for 10 minutes. Startup the CAM laptop, saw the raw material etc. and then it starts without any problem. Seems that the moist makes some faulty circuits and blows the fuses.