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Thread: Error 420 Y Servo, Fanuc 6T & 401 alarm too

  1. #1

    Angry Error 420 Y Servo, Fanuc 6T & 401 alarm too

    I've got a 420 error on a fanuc 6t. This alarm occured in the process of troubleshooting a 401 servo alarm (which is not cleared yet!).

    The 420 alarm means that the position error stored in the memory is bigger than the allowed error. This is on the Z-axis of the lathe.

    The error popped up after pressing the limit switches with the machine on. On resetting the machine, the error doesn't clear now.

    I am wondering if there is a machine parameter that I can change temporarily? Any other suggestions?

    Additionally, I've got a 401 alarm, which from my reading (and now experience) is pretty general and can mean many things. One thing that's interesting though is that none of the LED's on the velocity boards are coming on. According to the fanuc maint. manual this is either a bad connection, or possibly a bad motherboard. Any suggestions on this one? The x-axis contactor isn't pulling in.

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  2. #2


    Replaced x axis servo velocity board. this cleared the 401 alarm, and the 420 alarm cleared as soon as I put the machine back at the origin.

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