Mori Seiki SL-25 X axis Runaway On Power Up
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  1. #1
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    Default Mori Seiki SL-25 X axis Runaway On Power Up

    I desperately need some help! I have a Mori Seiki SL25/B500 Turning Center with a Fanuc Series 16A MF-T6 Control.

    On power up, when the servo amp initializes the x axis immediately runs away either to positive OT or negative OT switch and then the machine alarms out. I disconnected the x axis and with the motor power disconnected, everything else works fine. The z axis can be jogged and homed, the spindle runs fine, the tailstock works and the turret indexes fine. It's just the x axis that I cannot figure out. The machine got hit with a power spike a while back and the encoder was fried along with the servo amp and a few relays/fuses. I replaced the encoder (serial A pulse coder, 1,000,000P/rev) with a new one that Fanuc told me was a equivalent plug and play serial A pulse coder. The control has a new axis card and the encoder is picking up the movement of the axis correctly.

    I tried switching the axis control cards inside the servo amp, the isolation amp modules, and the transistor modules between the L and M axis but the problem remains with the x axis. I also de-soldered the 3 contactors and cleaned the contacts as they were sooty (the new servo amp is used but supposedly came off a functioning machine) but the problem remains still.

    I even swapped the signal cables for the x and z axis and checked the continuity of my encoder cable and everything checks good. I called Mori Seiki and Fanuc and they were of little help, so if anybody has any input or ideas I would be ever so greatful.

    The servo amp is A06B-6066-H244, 2 AXIS CONTROL, ROM VERSION: 001F
    Last edited by airpartsmfgtx; 11-28-2021 at 04:17 PM. Reason: Added additional details on servo amp model.

  2. #2
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    Had a runaway Z axis upon startup on a 2005 Haas horizontal mill. Not being much with electrical troubleshooting, I prayed it was a mechanical issue. Climbed in and pulled back the Z way cover (over several hours) to reveal a chip on the limit sensor. The machine was constantly getting feedback that it had reached the limit and was trying to back off a hair. Removed the chip and hammered the sheet metal flat again to hopefully prevent further chip ingress. Worth investigating if you haven't yet. Good luck!

  3. #3
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    That is something I am going to investigate right now, I didn't think about the magnetic switch but come to think of it both the limit switch and magnetic position switch are both covered in waxy resin and there was a lot of chips when I pulled the turret cover off. I am going to check that out (as soon as I finish dinner lol) and I will report back, thank you for your input I appreciate it!

    -John

  4. #4
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    Deceleration switch and limit switch both checked out fine. I did think of something though, I have had a faulty surge protector that was built in to the amp a long time back on my other Mori lathe. The internal capacitor I guess had broken down and it was causing the amp to behave strangely like axis erratic random movements and even ground faults that caused the machine contactor breaker to trip. I remember it was the x axis at first and then the z axis began moving erratically too. I suppose the best way to test my theory is to lookup the axis movement command signal in the ladder with the motor disconnected and see if the machine signal is triggered on power up or not. It's a long shot, but maybe I just might get lucky and be correct in my theory. I'll report back on what happens.


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