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The raster collapses, as though the set has been switched
off, reappearing a few seconds later. This can happen two or
three times, then the set will settle down with no further
trouble. There’s also intermittent loss of field hold, and poor
field linearity (top elongated).
For the loss of e.h.t. (picture collapse), open the right side
compartment flap to expose the 3AT2 e.h.t. rectifier and
check with a neon tester – the neon should light up when
brought near (not touching) the valve. You should also be
able to see the glow of this valve’s heater. If the neon
remains alight when the picture goes off, see if the heater
fades out. If it does, make sure that the e.h.t. is discharged
and then remove the valve base to check the heater contacts
and the 2.2C2 series resistor. If the neon goes out, check the
line timebase valves and voltages. The line output valve is a
31JS6A and the boost diode a 17DW4A. The field trouble
should respond to a new 17JZ8 field output valve. If
necessary, check its cathode bias components and those in
the linearity network.

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