PYE 693 CHASSIS
The set gives excellent results but there appears to be an
intermittent power supply fault. The mains lead, plug etc.
are free of physical defects, but when the set is switched on
from cold the raster and sound collapse then return within a
split second – as though there was a momentary power
supply interruption. This happens up to a dozen times, after
which the set operates normally.
The trouble sounds like a thermistor with a dry -jointed
end. The one to suspect is the surge limiter R305 (VA1104)
in the h.t. supply, on the panel behind the e.h.t. box. A
disturbance test should show a spark at the offending end.