Fanuc 6t dc motors "jitter" then says servo alarm? - Page 3


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Thread: Fanuc 6t dc motors "jitter" then says servo alarm?

  1. #25
    Registered tc429's Avatar
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    the T/M controls use the same hardware...on lathe chips are X/Z/Spindle, mill its X/Y/Z axes.

    I havent looked at a SCR servo board in a long time, but am pretty certain the axis card with the supply on it will have labeled test pins on it for a meter/scope. might look there next for a noisy supply...almost a certainty that at this age the caps will have degraded... gotta be really careful on those 'fold down' drives/boards...lots of high voltage- those gave me the creeps, I usually locked out, put jumpers to a remote terminal strip before power on testing anything on them...


    with the turn-off problem, does it come right back on, or do you need to press 'off' before it will restart? the fanuc supplies usually 'latch' off if a 24 volt short occurs (usually a wet OT/Decel limit switch) and wont reset without pressing 'off' first. on a 6A, I dont know though...all the newer stuff after 6B had a green PIL light for power, and a red 'fault' light for indicating supply overload...
    If theres no shorts, I'd ohm check the 'off' button...last few years had a lot of them fail, usually theyll get to 5~20 ohms before they start totally flaking out, but they should be <1 ohm...If you can thump on the control near the buttons and shut it off, its bad.
    I usually just clean them- the 'Fuji' blocks are black for open, brown for closed. take the wires off, the terminal screws OUT, remove the block to a safe/well lit bench, use a pick to slide the brass tabs(that held the terminal screws) straight out while holding the actuator in...once the tabs are out, the actuator/contact/spring will pop right out- dont let it fly just lightly scrape the silver pads with anything, theyll be good for another 20 years with under 1 ohm. once youve done it, you can clean/reassemble the block in a couple minutes, its really easy long as you dont drop the spring and spend a half hour searching for it

    Last edited by tc429; 10-13-2011 at 06:50 PM.


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    You cant just press the on once this happens, you have to push off, then on.



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    Quote Originally Posted by blakemachine View Post
    You cant just press the on once this happens, you have to push off, then on.
    usually means a 24v short to ground somewhere... bet you got a switch full of water and powdery white corrosion

    with the 'other' problem, this could be a great thing- something slightly arcing might be intermittently causing ground issues too

    the decel and overtravels are all NC contacts- if youve got a good meter that will read to .01 ohm resolution, start checking(power off) ohms to chassis ground on your switch wires in the cabinet- as theyre NC, theyll all read kinda low but the lowest reading should guide you directly to the culprit switch. if they all read pretty similar, it might be like a turret switch...if N.O. contacts though, might be a little harder to track down



  4. #28
    Community Moderator Al_The_Man's Avatar
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    With power supply shorts on the 6, I usually disconnect each of the 24v conductors leaving the terminal strip on the end of the P.S. one at a time, to see when the fault clears, same with the 5v terminations.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Once it does the shut off thing, this is the only alarm lights that I can find once this happens.

    THe first pic is with it running correctly, the second is when it shuts off.

    Attached Thumbnails Attached Thumbnails Fanuc 6t dc motors &quot;jitter&quot; then says servo alarm?-img_0892-jpg   Fanuc 6t dc motors &quot;jitter&quot; then says servo alarm?-img_0893-jpg  


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    I should also add that after it warms up for about an hour and turning it back on after it turns off multiple times, it seems to do it alot less if at all.



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    Quote Originally Posted by blakemachine View Post
    Once it does the shut off thing, this is the only alarm lights that I can find once this happens.

    THe first pic is with it running correctly, the second is when it shuts off.
    almost certainly a 24 volt short *somewhere* in the machine (the red light latches on after a delay if signal pa/pb doesnt return from the supply, so rarely could be a supply problem causing it, but 99% of the time its simply corroded terminal blocks or switches sinking the 24 volt output).



  8. #32
    Community Moderator Al_The_Man's Avatar
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    I have had short on the 5v as well as 24v that can cause the shut down, the unit you show is called the input unit, there is a jumper on this that will prevent it shutting down that allow for calculated diagnosing, but this applies constant power with the fault present.
    Your best bet I believe is to remove each terminal connection in turn to see which what causes the shut down.
    The intermittent ones can be very hard to find.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Shorts on the 5v and 24v can be a tricky thing.. they can end up all over the place. Watch for arcing. Water in switches.. Dirty contacts.

    Al is right.. the intermittent ones are the worst to be able to find.

    Watch all your grounds.. try to find leaky components. Loose wires..

    Make sure you have your electrical drawings. The engineer that helped me with my machine(s) sent me all of mine in PDF. A good retrofitter provides some documentation of wiring and cabinets.

    Watch the machine side and how it interacts with the NC/PMC/CNC and vs.



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    Default Re: Fanuc 6t dc motors "jitter" then says servo alarm?

    Hi. Not sure if this is the route to take to get some help but I'll try. We have a Fanuc OT control that sat for some time and, yes, the batteries died. It came off of an old, huge American lathe, and had very little use after the retrofit.We are now hoping to use it on an Okuma. It is a control with no PMC, and the motors are AC, and we have separate encoders to mount onto the ball screws. We have it set up away from the machine now, and have it powered up. There is communication from and to the rs232 port. There are no errors or alarms, but when we try homing, jog, or handwheel, the axis drives are not getting the signals from the control to turn. With Estop released the axis motors just slowly creep about one rev. per hour. When I push in the Estop and turn the encoders, they update position on the screen, but when Estop is released the encoders do not update the position. So with the encoders coupled to the motors we eventually get alarm # 411 and 421. We also have the Axis Inhibit light on the control panel ON. We have gone through all the parameters, but there may be a one we have missed. Any help would be much appreciated.



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    Default Re: Fanuc 6t dc motors "jitter" then says servo alarm?

    Please make this a new post.



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Fanuc 6t dc motors &quot;jitter&quot; then says servo alarm?
Fanuc 6t dc motors &quot;jitter&quot; then says servo alarm?