Problem with OMS/Step Pak

[Mark Rivers <RIVERS@cars3.uchicago.edu>]

    Folks,

I am writing to describe a strange but serious problem we had last week with
a OMS58/Step Pak motor system.

The symptom was that all 8 motors on one OMS/Step Pak started moving
spontaneously at about 2Hz.  This began when no one was around.  The motors
continued moving past soft limits and hardware limits, finally stopping only
when couplings broke or motors stalled.

Rebooting the VME crate did not stop the motors from moving.  Powering the VME
crate off did, but they began moving again immediately when power was turned
back on.

The problem turned out to be the OMS was not making firm contact with the VME
crate connectors.  Unplugging the OMS and plugging it back in firmly, and
screwing in the screws (which had been left loose) fixed the problem.  I found
the tmotor task was in the SUSPEND state when the problem was first noticed.
This means that the OMS had originally been making good contact, so the motor
task found it, but then had come loose enough to stop communicating, crashing
the motor task.  We don't know what module (OMS or APS transition board) was
generating the spurious pulses which were going to the Step Pak.

Moral of the story - make sure you tighten the screws on your OMS boards in
the VME crate.

                                   Mark