THORN 1400 CHASSIS
The receiver was working normally, then all of a sudden the
raster went off, leaving the sound unaffected. On checking,
I found that the fusible resistor R145 had gone open -circuit,
removing the h.t. supply to the line timebase. R145 goes
open every time I reconnect it, so I can’t check voltages.
What do you suggest?
A 220pF 8kV disc capacitor for third harmonic tuning is
connected between the cathode of the boost diode and
chassis. It’s mounted across tags on the line output
transformer. Inspect this, and if it looks upset (blackened)
replace it since it has probably gone short-circuit. It must be
a round disc type, not a tubular one. If this is all right,
check the line output stage valves – the PL504 and PY801.
If these are in order and the fusible resistor holds for several
minutes, during which the PL504 overheats, the trouble is
due to lack of line drive. In this case the 30FL2 line
oscillator valve and the associated components will have to