The screen went black, except for a few streaky lines like
ignition interference, whilst viewing. We thought that the
transmitter may have gone of, but on changing to another
station the screen went completely blank. The e.h.t. rectfier
is a stick type, and a.c. sparks can be obtained at either end
after making contact with a screwdriver. The line timebase
valves have all been replaced, but there is still no picture. I
suspect the line output transformer, but as this is expensive
would welcome your opinion.
If you find that there’s a negative voltage swing of
around —50V at one end of R425 (i.e. at the PL504’s control grid) this denotes the presence of line drive and the line
output transformer probably does have shorted turns. First
however see whether a neon tester lights up when placed
near the transformer with the e.h.t. rectifier disconnected. If
so, the e.h.t. stick rather than the transformer is likely to be
the cause of the lack of e.h.t.