If this is the K30 chassis there is an electrolytic capacitor on the A1 supply located top middle of the panel near the A1 control I think it's 4.7 mfd at 400v volts. This is a dim distant memory so don't quote me on that ! But it will be around that value.
It would dry up and cause brightness and greyscale problems on this and the KT3 chassis.
I think we used to replace it with a 10 mfd for some reason which I can't remember...
Worth a look.
Rich.