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For some time I’ve been troubled by varying loss of colour
on this set. The only way I can obtain a colour -killer bias is
to trigger the ident transistor TXd15 by linking its base and
collector. The transistor has been changed, also the emitter
and collector decoupling electrolytics in this stage and the
burst amplifier transistor, but the problem remains. After
triggering the ident transistor the colour may remain for
anything from five minutes to three days.
This set is getting old, and its performance will be
deteriorating. An unofficial modification to increase the
output from the ident amplifier stage is to short out the
undecoupled emitter resistor Rd87 (4.752). Cd57
(0.0022yF) which tunes the input to this stage is also worth
replacing. Other capacitors worth checking are Cd44
(50µF) which decouples the collector of the burst gate pulse
generator transistor, Cd45 (2,tin which decouples the
collector of the burst amplifier transistor, and Cd62
(0.03µF) which tunes the ident output circuit (if it’s of the
polystyrene type).

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