[jimmytek]

The machine is a Fanuc Robocut alpha-1iA, with display Series 18i-w. The unit uses three main servos: A06B-6081-H101 (power supply unit); A06B-6096-H201#CUT, and A06B-6096-H301). Preliminary troubleshooting showed the H301 down (nothing displayed, not even the dash). Eventually I found the fuse blown, and decided to send the unit to repair. Meanwhile, I verified for any short circuit in the cables that goes to the motor and found none. I got back the unit repaired, and put it back in place. Now it turns on with the dash, but never changes to a zero. The other two do change to zero, but goes back to dash again, all at startup. I verified the startup relay activating, and there's a voltage present on the upper bus of 296vdc that shows up while the first two units have a zero; but the voltage disapears when the unit goes back to dash (as expected). 24vdc is ok and reaching all three units. Plugs look ok. Does this means the third repaired unit is still defective? Is there something I'm missing? I do not have another unit to replace with. Any ideas will be appreciated. Thank you in advance.

[Mike283]

Check to be sure your contractors that supply power to the servo drives are working properly. Let me know if you need more help.

[STLMachinist]

1. If you unplug the feedback from the 3 axis, along with the motor power, and try to boot up, do you get the same thing?
2. Try switching the JX1A/B cables from the 1st->2nd, with the 2nd->3rd drives. Does anything change?

[jimmytek]

The dc power (24vdc) that comes from the power supply servo to the other two units is present. I interchanged the cables supplying the DC power supply and the problem remains.

[jimmytek]

1. I unpluged the 3 axis feedback and turned the unit on; the problem remains. I don't understand what you mean with unplugging the motor power.
2. I switched the JX1A/B cables; no change.

[STLMachinist]

Nothing external is causing this issue. Therefore the drive was not fully repaired, or possible parameters are not set.
If possible, can you check DGN 358 under System->DIAG. I'm unsure if this will be on your version of control, but it will tell us what the possible issue could be.
Also, try switching the fiber optic cables too. Just in case.

[jimmytek]

Ok, I have only one short fiber from the H201 to the H301. The other two are very long sections (very well tye-wrapped); one goes to what seems to be a main board, and the other to a smaller servo. Well, anyway, I switched the ends of the fiber optics cable (end of H301 to H201 and viceversa) but it behaved the same. The main screen has a DIAGNOS section, as shown below, and an AUF DGN. sub section (29).
Attachment 297724
SYSTEM has details on versions of the software components, but nothing more. AUF DGN. shows a screen with a machine misalignment, which is not possible to fix because machine never initializes well. Notice the 401 servo alarm in red on top of the screen. Section 26 of DIAGNOS gives details on the three axis affected, all from the same servo that does not initialize.

[STLMachinist]

Check under subsection 27. That should be the machine diagnostics.

[jimmytek]

Ok, it shows normal machine diagnostics, but nothing that indicates error. The picture:

[jimmytek]

I followed your advice, and resent the drive for a warranty repair. They accepted it and when it came back, the machine worked! Thank you so much. You're a real help.