This becomes apparent when the INFODISP on lpss12 stalls or disappears, and when TCS related commands cannot be issued through the ICS/DAS interface anymore. Additionaly, no telescope related headers are transfered to the FITS files and to the night log. These are all symptoms of a crashed TELD task.
On the TCS Xterminal, check whether the TELD task is still running. If not, start another telnet session to lpas1, login and type OPTIONS. Then type TELD to restart the task. Do a STARTOBSSYS on lpss10.