Trouble shooting a Fanuc control
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  1. #1
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    The company I work for has a CNC turret punch with a Fanuc control. I believe it is a 160 but I can't remember.

    The machine will run fine and then we get a 970 NMI error saying the OPT3 board failed. There is no pattern to the error, it can appear at any time with any program.

    We had a Fanuc tech come out, and he checked our electrical supply which was in spec. He then replaced the OPT3 board, then tried replacing other boards. We finally ended up with all new boards in the control and still get the error.

    Has anyone had any expeirence tracing down an error on a Fanuc system? The "plug n pray" method of chaning boards is not cutting it. The LED indicators on the control board give a general alarm nothing specific.

    Any ideas or suggestions? Thanks

  2. #2
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    I was a Fanuc service engineer many years ago.

    The NMI error is a "Non Maskable Interrupt". This alarm will means that the CPU has been halted. The CPU is designed to "fail safe" and not let the servos run away and crash, so the NMI alarm shuts down the servos also. It's a pretty unusual event, and from my experience it rarely happens in the field.

    Since you've replaced the boards, I think it's very unlikely that you have a HARDWARE problem on the boards. The likelyhood that you've have TWO boards with the same problem is astronomical.

    With the boards ruled out, that leaves a SOFTWARE bug or an external event, such as ground faults or EMI (Electro Magnetic Interferrence), or possible a power supply problem.

    The power supplies on these newer controls are "switching" type supplies, and they are pretty much immune to the stuff that used to affect the old style power supplies. They always have voltage sensing and overcurrent protection, so a bad power supply would likely just shut down rather than let the CNC run with poorly regulated DC power. It's still possible that you have a power supply problem, but personally I doubt it.

    From your description, we can rule out software also, since a software bug or a corrupted executive program will malfunction in exactly the same way every time. You say that your problem "has no pattern". A software problem would pop up at the exact same point in the program, or whenever you tried to use a particular feature of the control. I'm sure you would have noticed a pattern like that.

    Logically, that leaves us with an EXTERNAL event that's upsetting the applecart. A poorly grounded CNC control cabinet can leave the control vulnerable to EMI sources that are closeby. Are there any obvious EMI sources near this machine? I'm talking about anything that throws a spark, like an arc welder, spot welder, large motor starter, etc. If it's EMI, you may find that SOMETHING nearby is happening at the exact moment that the NMI alarm happens.

    Ordinarilly, the CNC cabinet is supposed to be a good EMI shield, but that assumes that the cabinet is well grounded. Check to be sure there is a good ground stake very close to the CNC cabinet, and that a large diameter stranded wire connects the grounding lug in the control to the stake. Also check those little wires that ground the CNC cabinet doors to the rest of the cabinet. The hinges on the doors can't be relied upon to ground the door. Also check the cabinet door gaskets to be sure they have not been replaced with non-conductive rubber gaskets, like automotive weatherstripping. The original gaskets have a lot of carbon in the rubber, and they're conductive. And ... for God's sake .... DON'T run the machine with the doors open!.

    Another possible cause is overheating of the control. Be sure your fans are running on the air-to-air heat exchanger on the CNC cabinet. A bad fan can cause lots of grief. There may also be some internal fans to circulate air within the cabinet.

    If you have any welding equipment nearby, try running the machine for a while with all the welders shut down. If it fails anyway, then EMI from the welders are not the problem.

  3. #3
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    "Trouble shooting a Fanuc control"

    Did you remember to turn off the safety before pulling the trigger?

  4. #4
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    In the past i have serviced manual presses, and 1 case in particular comes to mind.
    It was a press with a shifting table (back-forth-down-up).
    Every once in a while te press errored.
    The problem was that when the table shifted, the shock it created by stopping caused a few relais in the cabinet to move a few MM sideways, after years it caused a few cracked wires.

    So my advice would be to watch closely into the cabinet while the machine punches, and observe wich parts bounce or absorb vibration.


    Ofcourse taking precaution with the electricity!

    Question for Dan, the Fanuc tech replaced the board, but that board goes into a slot, is that slot also a motherbaord, or is it only a pin-connector, and is it much work to change that aswell?
    I tend to think that it would be more logical to do just that, then changing boards that the control doesnt pinpoint as erroneous

  5. #5
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    Wow, didn't expect this much help but I sure do appreciate it.


    "Trouble shooting a Fanuc control"

    Did you remember to turn off the safety before pulling the trigger?
    Funny you mention that. The plant manager has said he just might have me come in with my .50 BMG and put the machine out of its (and our) misery

    I made a mistake in the type of error. Here is the exact message:

    972 NMI in other module
    Slot 03
    PC150 NMI SLC 83-81

    Are there any obvious EMI sources near this machine?
    Yes there are welders but both the welders and machine having been in the same place for 7 years. So I doubt that would suddenly cause the error after that amount of time, and the machine will error out even when there are no welders operating.

    Check to be sure there is a good ground stake very close to the CNC cabinet, and that a large diameter stranded wire connects the grounding lug in the control to the stake
    There is a seperate transfomer taking the 440v down to 408v. The power then feeds into the main voltage cabinet. This cabinet has a large copper ground rod set several feet into the earth. The control cabinet sets roughly 3-4' away from the main cabinet.

    Another possible cause is overheating of the control.
    We put a box fan blowing onto the control boards with the cabinet door open. (yeah I saw where you said not too....) We cleaned the filters and checked all cooling fans. The extra cooling made no difference.

    So my advice would be to watch closely into the cabinet while the machine punches, and observe wich parts bounce or absorb vibration
    The control cabinet is a stand alone unit, connected to the punch press only thru conduit. Not much vibration. However we are wondering if there isn't some wiring/electrical gadget on the machine itself being vibrated. This might short out and cause the error...

    then changing boards that the control doesnt pinpoint as erroneous
    The Fanuc tech told us that the entire system is "daisy chained" together. An OPT3 error doesn't necessarily mean it is the OPT3 board. Fanuc replaced the boards with new ones to see what would happen. They didn't make us buy the new boards, we just paid labor to have the tech there.

    Thanks again for the help and suggestions, and if we do end up going with the "fifty caliber reboot" I will post pics!

  6. #6
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    an open cabinet door, a UV bug light and no covers on the EPROMS will convert a machine into something else - like a galactic warblefuzzer.

    Not good - recheck your cabinet fans for rotation and their direction

  7. #7
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    an open cabinet door, a UV bug light and no covers on the EPROMS will convert a machine into something else - like a galactic warblefuzzer.

    Not good - recheck your cabinet fans for rotation and their direction

    I agree on the the vibration issue - I've had punches shut down because the slug bin door sensor jerked - something about a 4 1/2" hole through 3/8" stainless goes WHOMMP!

  8. #8
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    Would love to see pic of a "fifty cal reboot."


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