Sorry for the delay, I've spent the last day in hospital so I couldn't write back!
I suspect the problem is the +200V supply to the video amplifier stages is missing or has dropped very low. Please do the following and tell me what your meter reads:
CAUTION - There are very high voltages near to where I need the measurements, be very careful not to directly touch anything!
Measure on the small circuit board at the back of the neck of the CRT. It might be marked "CPT PWB".
1. use a DC voltage range suitable for measuring up to 1000V.
2. locate the connector (E805?) that has 7 wires going to the main board.
3. Find pin 1 of the connector, if they are not numbered, it is the one that links to R811, R812 and R813.
4. Connect the red meter probe to that pin.
5. Connect the black meter probe to pin 3, they are numbered sequentially. If it isn't marked, pin 3 connects to R804, R805 and R806 as well as several other components.
6. Switch on.
The voltage should quickly rise to about 200V before it shuts down. Please let me know what it actually reads.
Brian.