There is a heater for the vidicon which had to be shut off due to power budget. This heater had been on since launch. After being switched off, turning on this heater back on, or the vidicon's cathode filament (itself a separate heater) would have cracked the tube due to the cold of space.
(The HV supply on a vidicons is usually about 700V—that's high enough to be quite stressful on P/S components.)