The fault is a dark screen in the centre. 1 can just about see the lines in the raster at the
top and bottom. By adjusting the brightness
control, it makes the raster disappear. I have
checked all the voltages at the c.r.t. base.-H.
Kirby (New Barnet, Hertfordshire). Check the 10F1 video amplifier valve. If this
is not at fault (heater -cathode insulation failure) check the 6D2 and vision i.f. 10F1 valves.