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Thread: 401 servo alarm (VRDY off)

  1. #1
    Join Date
    Jun 2006

    Default 401 servo alarm (VRDY off)


    I've Puma 6s with fanuc 0, after applying the lost parameters, i found the mentioned alarm,

    could any one help me to solve that.


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  2. #2
    Join Date
    Mar 2007

    Default 401 servo alarm

    Check your circuit breakers first in your electrical cabinet if the are all alright then check your optical cable that connects the servo drives. Here is a screen dump of your error and the actions to take.

    Attached Thumbnails Attached Thumbnails -untitled-jpg  

  3. #3


    SERV0 ALARM 401
    Which Fanuc Model & Axis Drive you are using. If it is Old analog & Digital Drive, Pl. check the 100V ac to the Drive. It is always through the Emergency Relay

  4. #4



    I have a mill with a Fanuc 0M controller. The drive hardware is siemens...

    I have the 401 servo alarm (VRDY off) that is thread is about...

    It all started one day after the machine was off for about 2-3 months. I had to turn it off, and back on about 8 times to get pass this 401 Error.

    What is it does is upon power on, I hear one relay.. the screen shows some software numbers, and then jumps to the XYZ 00000 screen like it always had before, but now, it sits there about 5 seconds like it wants to work, but I hear another relay trip and up comes the 401 servo alarm.

    I have looked at the parameters, but I really do not know what they are suppose to be. I purchased the machine 5 times ownership old, and no books or parameter papers came with the machine. Also, it seems that the siemens controller is not popular with people.

    I have changed the motors around, and it does not help. They are all 3 the same according to the tags on them. I have pulled the controller board, and this appears ok..

    There are some LED lights that come on.

    First on bootup, a green LED pops on, and then back off. When the machine CRT displays the XYZ 00000 screen, all LEDs are out, and then that relay trips and a red one on the SIMODRIVE 6RB21 board lights up ( V5 ) at what appears to be the Y axis set of lights. Then the green one, and a red one comes on at V4 and V1

    So, somehow I think it is the limit switches, but they are all free and I hear relays clicking. I can put some wedges in the switches like the machine is home, and the error does not come on, but neither does the machine. the boot up hangs at the software version screen and will not continue to XYZ 00000 screen. Pull the wedges, and it will continue to boot, but then 5 seconds or less, the 401 Servo Alarm....

    Any ideas?


  5. #5


    For the Siemens drive.
    Check the dc link voltage at the axis drive.If it is ok,check the drive healthy signal which is 24vdc and goes in terminal 73.2 and comes out 72 or vice versa on the axis drive.If you do not have the healthy signal the problem is in the drive.These older drives do not like dampness.If they have been standing a while disused in a less than dry atmosphere it is better to give them a blow with a heater for a few minutes before powering up.

  6. #6


    I would need a little more definition of what these items are called for a mill tech vs a master mech and computer engineer..

    I call the drive axis motor.. just plain electric motors.

    I call the SimoDrive a computer controller.

    I call the Fanuc a user interface controller.

    Now, checking the axis drive sounds to me like checking the computer controller at some test point.

    The drive healthy signal at 73.2 sounds like some test point on that big cabinet where there are many wires running around.

    What is a axis drive... what does not like dampness. Because I sure have alot of humidity in my shop. No heat or AC, so temp inversion is really bad some days.

    Its hard for me to understand that it will boot up and sit there about 5 seconds sometimes and it wants to work, but then that relay will trip and the 401 error comes up. I can disconnect the encoder plug and get X error communication, and then take off Y and get the same error.

    thanks for your help, I need to make some parts...

  7. #7


    The Fanuc part is called the cnc control.
    The Simodrive is an axis drive and/or a spindle drive.
    The axis drive motors are servo motors.
    I`m afraid I cannot give any more help as the voltages within these components are lethal if you come into contact with them.
    I suggest you contact a cnc repair guy.

  8. #8


    I have had this machine for 3 years. I have worked around higher voltages than the 240 running around inside this cabniet. I wear and adhere to proper safty equipment and guidelines. I have a EE degree.

    I worked with the machine some more today. I called Fanuc and they suggest the problem is in the Siemens controller area. One time today, it booted to the ready state for about 10 seconds... in the past when it did this exact same thing, all I had to do was turn it on and off about 10 times and it finally stayed in the ready state.

    I think it is the 24v signal as this is what the Fanuc customer support indicated also. is it 24v DC or AC? I can remove the caps from the drive motors. I have already removed these 20 plus times. Even if it is missing 24v signal, what am I going to replace to fix this issue? I looked up all the boards in the controller.. I have the following with the XYZ conections... 6RB2100-0NA21, Control Board

    From what I remember it all started when I overran the table on the x axis, and worked fine the rest of the day, but when I tried to turn it on the next time, it did not boot up to ready. it was the error....

  9. #9


    There is a lot more than 230 volts running around this cabinet.The dc busbars will either be 210 or 320 volts.These are open and run along the botton of the axis control.
    The old dc drives do not like dampness,stray voltages short on the cards and cause failure,sometimes with a very loud bang.This problem is not confined to Siemens only.
    Yes the problem is in the Siemens unit.The Fanuc control is not getting a drive ready/healthy signal.It is 24vdc.It comes from where I told you.Have you checked the dc fuses feeding the stack cards?
    It is possible to remove axis cards and make the drive think there is only one or two axis but you need to know what you are doing.
    If you have elec schematics for the machine you will be able to follow this signal if you are an EE.
    If the fault is not obvious to me I have spare cards and can replace each card until I find the faulty one.I also isolate the Simodrive from the cnc and set each axis up using a battery box.It is relatively easy to do as Siemens always uses the same terminal numbers from drive to drive.
    What make is the mill?

  10. #10


    No schematics to the machine : ( I am about number 5 owner... I purchased the machine without parameters even loaded. I was lucky enough to fine a phone number on a piece of paper in the machine that was for AIT in CA.. Sidney was the person who built the machine in 1989... it is a WebbMatic 800 with this lovely Fanuc Om-A and the Siemens controll.

    Sidney sold me the parameter sheet, and I loaded the machine and got it working. It never has zero home correctly since I have had the machine, but my work is not that precision, just needs to look pretty.. The machine is very tight, so I would like it to work a little more. The spindle head is nice, and not noisy..

    BTW... here is some of my work

    I am a hybrid engine installation specialists.. but I did computer networking and systems testing in the past also.

  11. #11


    You can download a manual for the 6RB2100 drive at the Siemens Automation and Drives website.It is a nightmare site to navigate but can be done.

  12. #12


    here is a pic of the inside... I marked the LED's that are on with the red arrows.

    here are the fuses... all of these are confirmed good.

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