BUSH TV315

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The brightness control had to be adjusted because the
picture got darker. Then both the picture and sound went.
On inspection the line output and boost diode valves appear
to have been overheating, there is a slight crack in the base
of the e.h.t. rectifier’s valveholder, and the line output
valve’s fusible screen grid feed resistor was found to be
open -circuit.
The overheating of the PL504 line output valve and its
screen grid feed resistor suggest lack of drive from the
EF184 line oscillator. Check this valve and the associated
components, especially the flywheel sync discriminator
diodes 3D6/7, the tuning and feedback capacitors 3C32
and 3C34 respectively, and the 10µF supply decoupling
electrolytic 3C31. If the oscillator is running however –
proved by -40V or more at pin 1 of the PL504 – suspect
the boost capacitor 3C44 or the line output transformer. If
the surge limiter resistor 3R67 which is fed from pin 2 of the
line output transformer is overheating change the associated
l.t. supply rectifier 3D8 (BA148). (Rank A774 chassis.)

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