DECCA 30 SERIES

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This Decca 30 series chassis is actually in a Telefunken
model. The picture is very good once the set settles down
after the first few minutes, but some odd things occur initially.
After switching on, one usually gets to start with a very
dark, diffused picture, mainly in blues and greens. Then the
screen becomes almost entirely white, with very pale
colours here and there. Eventually a vague picture is seen,
then a hissing noise occurs accompanied by dark lines
across the screen. Then the picture comes up much clearer.
It seems to us that the most likely cause of these symptoms is simply that either the PL509 or PY500 line output
stage valve is lazy. Alternatively, it could be that the c.r.t. is
loading the e.h.t. generator due to its being driven hard as a
result of a fault on the decoder panel. This would show up
as an abnormally low voltage on all three cathodes, and
could be due to a faulty MC1327P demodulator/matrixing
i.c. or a fault in the luminance emitter -follower (TR204)
circuit.

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