[leito1489]

Hello everybody, and first of all thank you for this space.

Before creating this thread I've been looking for old threads and found a few with the same alarm code, but the difference lies in the spindle drive they had. So here is my problem:

I have an old Mazak QT20 with a Mazatrol T1 control. The spindle drive is FANUC MODEL 15 I think. The number on the drive board is: A20B - 0009 - 0534

The alarm code is number 55 : motor overload. I got this alarm from time to time before, mostly in high humidity days, but It never persisted. Usually I ventilated all the cabinets and a few minutes later the lathe was ready to work.

Yesterday the alarm showed up again, but this time more frequently, and it's impossible to work with the machine. Today the same, I can't reset the alarm, not even switching off the general switch like I always do. There are four leds in the fanuc drive board numbered 1 - 2 - 4 - 8 I think. The 8 and 12 are glowing. I don't have any documentation about this drive, so I don't know for sure where to start.

I have to mention that the first day this problem started we had a problem with one phase in our workshop. The phase was still there, but it couldn't be detected by a multimeter, anyway the machines were working ok. The problem was a faulty lamp that was almost shorted. A strange case, in fact when I used the multimeter to check that phase it showed 0 volts with the tip of the multimeter in contact, and when I retired the tip, for a fraction of a second the voltage raised in the multimeter and then droppend again. I suspect that this has something to do with the malfunction on my lathe, but I'm not sure, anyway I think it's important to mention it. Now the phase problem is corrected, but the lathe still has the alarm.

Anyway, that's the deal, I'm practically without clues, I hope someone can give me a hand to diagnose the problem and take a measure about it because I need this machine to work. I'm even thinking in the worst case scenario (replacing the drive), but first I need to know what's happening there.

Thanks as always for your help and attention!

Leonardo Marsaglia.

[botha.y]

I do think you have a spindle load meter on your screen, what does it say when you turn your spindle for a couple minutes at all different gears and different speeds, check the load behavior. Very likely that you'll see the cause of the alarm there if it occurs.
Next, do put your machine in semi-closed loop, take out the motor from the machine, Turn it manually to check if it turns freely, then with control and again check if it turns freely. Then check the gears and check that they turn freely. Usually the Fanuc alarm 55 motor overload is pretty accurate and means there was an actual overload.

[leito1489]

Hello botha.y and thanks for your answer.

I was checking components, fuses, any loose solder, capacitors. and everything looks normal. I saw several posts over here showing that it's possible to change the spindle drive for another one of a different brand.

I'm planning to do that but I have several doubts about the signals that come out of the CNC to the spindle drive. As the manuals and schematics are really poor, I've been measuring and it seems all the logic signals from and to the Mazatrol T1 CNC are 24 VDC. I would like to know if any person of this community has experience to confirm that.

Now I have the ALARM 55 wich is the only one preventing the lathe to be fully functional. I'm planning to fool the CNC and make a bridge to ignore that alarm and then I can check all the command velocity voltages that I need for the new spindle drive. And that's what brings me to my other doubt. I've seen that all the cases here of drive failure were solved by using a Toshiba VFD. I'm planning to use a DELTA VFD wich has a +/- 10 Volts input for velocity. I suspect the T1 control has an analog output to tell the drive wich velocity the CNC needs. Do you know anything about this?

I will be very thankful if you can throw me a hand with this so I can be sure about the procedure for mounting the new VFD and put the machine at work as soon as possible.

Thanks in advance and please apollogize if I'm a little hurried.

Leonardo Marsaglia.

[botha.y]

PM MrMazak in this forum, he would know more about which I/O card with analog output to purchase for this control than I would.