Brightness jumping problem on B&O MS 6000 28" CRT TV

Hello all

Please could anyone help me, my ms 6000 has developed an intermittent fault where the brightness keeps going wild and when it goes bright it shows the spaced diagonal horizontal lines a bit lighter than the black background, it is as though someone is playing with the brightness potentiometer on the tube.

I've tried to adjust the potentiometer myself and it doesn't stop it. It is weird as it stopped happening for about a month, and now has started happening again

Thanks to all

Try adjusting the focus and see if the brightness fluctuates as the focus is adjusted. If that is the case, I would suspect a short in the CRT, focus to screen grid. You can also look to see what is happening to the voltage on the CRT driver transistors. If the B+ is dropping that feeds the collectors, it could be a bad filter cap on that line, usually not intermittent, or a bad solder connection.