Mitsubishi RV-M1 not homing correctly

[Jonas]

Hi all!

I've recently got my hands on a Mitsubishi Movemaster RV-M1 robot. The robot was installed on a CIM system, tending either a Denford Cyclone or an EMCO VMC 100 mill.
Unfortunately, both the lathe and mill were long gone, the only thing that was left was the robot + some cabling from the CIM controller itself.

I've put the robot on a pedestal for testing.
The control unit switches on, the teaching box seems to work, I can manually move all the axis and open/close the hand.
However:
When I try to home the robot using the NST command on the teach box, all the axis move to their respective limit switches, with J1 being the last.
After that, the robot just sits there, doing nothing. None of the buttons on the teach box or the drive unit seem to to anything and the green "EXECUTE" LED on the drive unit stays lit.
I get the impression that the robot is waiting for the homing cycle to finish.

On the back of the drive unit, there is an additional connector labeled "Option". The robot came with a corresponding cable + plug, but nothing to connect it up to. I believe this might be for an additional axis, to move the entire robot along a conveyor belt or between machines.
As I don't have an additional axis to connect to, my theory is that the robot is waiting for the additional axis to finish homing, which of course it never does, as it is not connected.

I've tried asking Mitsubishi Europe for any documentation for an optional axis, however they claim that no such thing ever existed, and for all I know they might be correct.
They also told me that one of the encoders on the axis could have a faulty Z index signal, but to me that would mean that this axis would not be able to home (again, all the axis on the robot itself home without any issues).

Basically, my questions are: Could my theory about the missing optional axis be the cause of my problems?
And if so, is there any documentation on how to disable this axis.

Any help would be greatly appreciated!

Jonas

[Jonas]

Here's a picture of the back of my drive unit:

9d485d91-5fab-44c2-9b26-64f1b93e432d - Kopie.png (2.74 MiB) Viewed 4277 times