DECCA CTV25

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This old colour set gives excellent results except for limited
colour and an unsynchronised PAL switch. Tuning for
maximum ident signal at the emitter of the ident emitter –
follower Tr603 with the ident coil L602, the burst coil and
VR602 (discriminator balance) produces a signal of about
7V peak -to -peak and about 8.5V across the colour -killer
reservoir capacitor C609. This gives reasonable but
intermittent colour, but the PAL switch runs unsynchronised – in fact it seems to favour green faces!
Reducing the amplitude of the ident signal results in correct
PAL switching but loss of colour.
You don’t seem to have enough ident signal. There
should be about 10V peak -peak at the emitter of Tr603,
with L602 adjusted for slightly less than maximum ident
signal. We’d suggest you check by substitution the two
electrolytics in the ident circuit, C611 and C614, both
10,uF. The ident should be improved by replacing the ident
diode D604 – use an 0A91 – and its coupling capacitor
C615 (0.22µF).

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