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Thread: Ground Fault Detected VF0

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    Default Ground Fault Detected VF0

    I'm getting a 175 alarm on my 1990 VF0:

    175 GROUND FAULT DETECTED - A ground fault condition was detected in the 115V AC supply. This can be caused by a short to ground in any of the servo motors, the tool change motors, the fans, or the oil pump.

    I have all three axis motors physically unplugged from the control cabinet, the tool changer unplugged from the control, the fan supply unplugged from the IO board, and the oiler unplugged from the control. I still get the alarm.

    Can anyone suggest any other potential causes I can look into?

    If it matters, the machine is powered from a Phase Perfect digital phase converter, 230V.


    If you're interested, the background :

    I bought a used (1990) VF0 5-6 years ago, set it up in the shop, ran it for less than one day, and suffered a short in the x-axis cable. Turns out HAAS did a poor job manufacturing the cable and left a ball of solder in the AMP connector that somehow during transit to it's new home made it's way between the +160VDC output wire to the motor and an encoder wire coming into the MOTIF board. End result, fried the MOTIF board and the I/O board. At the time, I called HAAS in to get an estimate to fix the machine; total price with labor was going to be ~$4000 which was about half again what I paid for the machine...I deemed it not worth the cost and waited to either find parts for it myself or retrofit.

    Since then, I scrounged two spare MOTIF boards from ebay (both claimed to be new) and replaced all the components on the I/O board that I assumed could go bad (namely all the ICs) and fixed the x-cable and checked all others.

    I recently got to putting the MOTIF board in along with the repaired IO board. Turned the machine (for the first time in ~5 years) and voila...control booted up with no apparent issues...until it spit out a "ground fault detected" alarm.

    I assumed this was due an issue in the axis motors (brush dust) so I disconnected (and disabled in the control) all of the axes as well as the tool changer, coolant pump, work light, and oiler. This didn't fix the problem. Then I systematically disconnected all outputs from the IO board and still couldn't get rid of the ground fault.

    Then I got stupid and decided to override the ground fault detection, enabled the drives, and bam...immediately fried an IC and resistor on the IO board (see recent post). After some checking, I found the MOSFET in the tool changer circuit had been bad (perhaps from the original short?) so I fixed this and the IC and the resistor.

    I assumed this had been causing the ground fault so I put everything back together this weekend hoping the ground fault would be solved...but it's not. With all axes and tool changer disconnected, I still get the alarm. After a full day of trying to track down where the ground fault could be coming from, I decided to override the detection again...this time no bad side effects...machine will power up and servos will enable. So what else could be causing the ground fault.

    Thanks,
    -Ryan

    Similar Threads:
    Ryan K. Dygert
    www.Empire-Engineering.com


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    I have found that the tool change solenoids or the solenoid cable shorts out. You have a solenoid for pre-charge and one at the Tool release piston. If your machine has a gearbox then you have a solenoide behind the mounting bracket for the Z axis cable track. On the I/o board you will see usually on the lower right hand side of the board a connection labeled something like "solenoid" or head Solenoids. Unplug this and see if the alarm goes away. Also another common cause is a worklight. Unplug the worklight cable.

    james



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    I've disconnected all of the outputs from the IO board (except the auto off) one-by-one and none of them got rid of the ground fault. I even tried powering the CRT and PC supply separately from house 115v power to make sure it wasn't in either of them...it wasn't.

    Does anyone know where the ground fault is sensed on this machine? Is it possible the ground fault detection circuit is bad?

    -Ryan

    Ryan K. Dygert
    www.Empire-Engineering.com


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    It sounds like you are doing all of the right troubleshooting checks. Just like you did initially when you can no longer think of anything else, turn off ground fault detection and look for the smoke, which you found.

    Were you able to tell what the burned components controlled by chance? Maybe point you in the right direction.

    If all the 115v devices have been checked, then you may have to run with the ground fault detect turned off. I would hate to see you fry more components by turning it off but I can't say that I haven't had to do it as a last resort.

    Also, did you send the I/O board out for repairs, or did you perform them?



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    The resistor & IC that fried was in the tool changer circuitry; this time I fixed the board myself. The first time it fried (after the x-axis cable short...see story above ) I took it to an electronics repair shop and just told them to replace all the ICs (I didn't know what had been affected that time but the HAAS rep that was out said the IO board was bad).

    Is it possible that the circuit that looks for a ground fault is bad itself? Does anyone know how the ground fault is detected? Also, is it possible that there is an incompatibility between the new MOTIF board I installed and the IO board or other components? The new MOTIF is a couple revisions newer than the original.

    What about the incoming power, could that be an issue? I've read on a few posts that the some HAAS's should have wye input power with an isolated ground, my manual doesn't specify this but my machine is supplied with delta power.

    Thanks for your input everybody.
    -Ryan

    Ryan K. Dygert
    www.Empire-Engineering.com


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    Make sure ground fault circuit is adjusted correctly.
    Adjust ground fault (R86) to 0.075V. Operate tool changer several times. If a ground fault alarm occurs, increase to 0.150V. Repeat test. If fault still occurs, contact your local Haas factory outlet for further support.

    Thanks,
    Ken Foulks


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    Ken,

    Where is this adjustment made? "R86" sounds like a resistor? Is this a potentiometer on one of the boards that you change to get the voltage drops you indicated?

    Thanks,
    Ryan

    Ryan K. Dygert
    www.Empire-Engineering.com


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    What Ken is refering to is resistor that sets the threshold voltage for the ground fault detection. Do you have a PN on the i/o board, some i/o boards came with a variable resistor you can adjust, some came with a pre-set value.



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    The board doesn't have a PN on it, it only says "IO board Rev C" and it doesn't have any variable resistors on it...

    Ryan K. Dygert
    www.Empire-Engineering.com


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