My 8568B display section has developed a fault, on which I would appreciate some where to start looking advice. The SA powers up fine and trace is normal. After a couple of minutes the display brightness starts flashing and I have to turn up the intensity to see the data as well as the graticule. A little later, the graticule and data gradually expand so that they are overscanned by maybe 100%, suggesting, perhaps, an EHT fault. If I switch off and let the instrument cool right down, the same sequence repeats. The display and RF section prefixes are 2601, 2542, suggesting that I have the display with the 18kV PDA. Having to make all measurements in a 2 minute time window is a bit of a restriction, so any advice gratefully received.