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On switching on, the picture does not appear for some time after the sound has come up. The
picture then remains for about half -an -hour before
it disappears leaving a dark screen. If the brilliance or contrast control is now advanced the picture will return once again but after a further hour or
two will become either of the
two controls must be retarded to correct brightness. The c.r.t. was replaced recently and nearly all the valves are new. The GEX34 diodes are also
new.-D. Earle (Birmingham 21). We are inclined to suspect the c.r.t. despite the
fact that it is a recent replacement. If it is a
regunned tube, we would advise you to send this back to the suppliers for their inspection. If the
tube is brand new, however, you will have to check
the video amplifier components with particular
reference to R18 (3.9kLi) also checking the voltage at pin 7 which, under normal conditions, should be 145V. Also check the bias voltage (3V) and the V6
and V7 pin 8 voltages.

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