Looking for Advice

[Joe1991]

So, ive got this old machine that uses fanuc servo amps motors and controls
We are having an issue where the first and second axis work fine but the moment you try to control the third axis it throws an abnormal current alarm.
Over a period of time, we have tried the following:
Sent the motor out for testing (came back fine so motor is good)
Replaced the motor power cable due to the manual recommendation(Power cable good)
Swapped servo amps (The problem followed axis 3 so Servo Amp is Good)
Swapped cables running from cnc to servo amps (They were fine)
Swapped motor feedback cables just in case, but that was fine too
Checked limit switches to see if they were not functional and somehow overriding the motor (again good)

I'm just looking for a direction to go.
I'm thinking the problem might be inside the OPT1, MAIN-C, PMC-NA, PSU-B1 combo,
But i'd like to know some of what I'm doing before i start taking things apart and erasing CNC data by mistake
Even confirmation this is the right direction to look in would be helpful

Thanks for the help.
If you need more info I'll gladly give it to you

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[Johneezreno]

How much slop is in the ball screw?

Sent from my SM-G950U using Tapatalk

[regina]

How much slop is in the ball screw?

Sent from my SM-G950U using Tapatalk

On this note, does it do it if the motor is electrically connected but not mechanically coupled? (bad bearing or screw or something, clamped axis?)

[Joe1991]

On this note, does it do it if the motor is electrically connected but not mechanically coupled? (bad bearing or screw or something, clamped axis?)

Yes, the motor throws an abnormal current alarm when electrically connected, no matter if its coupled mechanically or not.

[Jim Dawson]

You say 3rd axis, is this a vertical Z axis? Maybe with a brake?

It also seems that the common component in all of your tests is the motor. You had it tested, but is it really OK? Maybe insulation breakdown at higher frequencies/voltage?

This is normally the point that I rip out everything that says Fanuc on it and do a retrofit with modern controls.

[generaldisarray]

First, leave the control alone.

Who tested this motor? Stevie Wonder?
What are the Megohm values they got?

is this like a 0MC or 15M or what

[Joe1991]

You say 3rd axis, is this a vertical Z axis? Maybe with a brake?

It also seems that the common component in all of your tests is the motor. You had it tested, but is it really OK? Maybe insulation breakdown at higher frequencies/voltage?

This is normally the point that I rip out everything that says Fanuc on it and do a retrofit with modern controls.

The third axis is a B axis. So no, no real brake. My boss told me when he sent out the motor, they got it running fine. More recently, I megged it and it had good values. (Its an a6/2000 btw)
Whats weird is that when the motor is free, and I turn it on, it will rotate just slightly before it throws the abnormal current alarm.
I checked the parameters and they were good too

[Jim Dawson]

PulseCoder problem maybe?

[generaldisarray]

I dont know about the pulse coder. And we still dont know what series control it is. So it could be a pulse coder. It sounds like a pre-serial pulsecoder that is timed wrong. They will jerk when attempting to move and give some alarm. But I dont remember which one.
But I thought that they switched to serial before the "a" motors.

Is this a lathe?

at any rate I would snag another motor for cheap on ebay

[Joe1991]

I dont know about the pulse coder. And we still dont know what series control it is. So it could be a pulse coder. It sounds like a pre-serial pulsecoder that is timed wrong. They will jerk when attempting to move and give some alarm. But I dont remember which one.
But I thought that they switched to serial before the "a" motors.

Is this a lathe?

at any rate I would snag another motor for cheap on ebay

The control is a series 15B and this is an OD grinder. its an older junker

[drdos]

If everything checks out OK then I would test the CNC. The way to do that is change parameter 1023. If you have 3 axes you can change the first with the 3rd. So assume 1023 has 1 , 2 , 3 change to 3, 2, 1. Then swap the command cable (CV1 – CV3) from the first axis with the 3rd and do the same with the feedback (JF1 – JF3) if it goes directly to the controller. Also if you have scales (JF21 - JF23) If you do this correctly then everything will run normally. If the problem stays with the 3rd axis then it is NOT a controller issue. If it does then you will have to replace the servo control and servo interface modules on the main board.

[Joe1991]

If everything checks out OK then I would test the CNC. The way to do that is change parameter 1023. If you have 3 axes you can change the first with the 3rd. So assume 1023 has 1 , 2 , 3 change to 3, 2, 1. Then swap the command cable (CV1 – CV3) from the first axis with the 3rd and do the same with the feedback (JF1 – JF3) if it goes directly to the controller. Also if you have scales (JF21 - JF23) If you do this correctly then everything will run normally. If the problem stays with the 3rd axis then it is NOT a controller issue. If it does then you will have to replace the servo control and servo interface modules on the main board.

Ok, so i tried this, and the "abnormal current" problem moved to the X axis. So basically the modules inside the cnc controlling the 3rd output (JF3,JF23,CV3) is broken. Do you know if this is fairly simple to replace? Also, are these modules located inside the "Main-C," and should i be worried about clearing params/ ladder logic? Thanks, just want to know for sure before i start doing anything

[drdos]

You should always have a backup before doing this, but if done correctly you shouldn't lose anything.

[Joe1991]

Hello,

So an update, I bought the PCB's, replaced them today and the abnormal current error is gone.
I now have an excess error (Sv008) Popping up when i try to move the axis. Basically as i understand it the motor and encoder aren't agreeing.
The axis might be stuck, Apparently it hasn't moved in years. I'm going to take the motor out and try it that way just to see. + Check hydraulic lines...
Besides this, any suggestions?

Thanks

[Joe1991]

Machine is back up and running, thanks for the PCB help!