On your screen is a small pop-up called xshow. It shows a few quantities,
one of which is xdangle (the X-diserser angle). If this number is changing then you likely have an oscillation problem.
Go to the pulldown menu and under HIRES Control Menu, choose
Stop Cross-disperser Oscillation.
You may have to try several times to stop the oscillation. If the
oscillation continues after this contact an instrument scientist.
The X-disperser is still on manual:
After swapping in the new X-disperser, you may have left the controls
on manual. This may have prevented the cover from opening and/or the
angle from changing so that the zeroeth order falls on the CCD.
The X-disperser cover is stuck:
Even though the controls may be on remote, its possible the X-disperser
cover may be stuck closed. Look on XHIRES to see its status.
There is a cabling error:
After swapping in the new X-disperser, the control cable was not
re-connected.
