ideas:
1. Corrupted eeprom values, many that cannot be changed in the service
menu.
2. Bad capacitors in the HOT or PIN circuit.
3. Yoke, which means new CRT.
4. Power supply regulation problems.
5. Flyback.

and several others.

You simply need to do standard full troubleshooting and check all the
output components. The fact the image pulls in on brighter images
indicates either poor b+ regulation or a problem with too much current draw
in the output stage.

David