Your first email seemed to imply that sometimes it was working for a few seconds, hence the before and after suggestion. Anyway, measure all the low voltage rails and if any are significantly low measure the voltage across the current monitoring resistors R982 for +5V and R940 and R943 for +/-20V. If you can get at the deflection plates try to measure the voltages there as well. The high voltage supply to the CRT is from the unregulated 33V so that can continue to run despite a fault on the regulated supplies.
Regards,
Roger
