The “Battersea” Chassis
Model: Decca CTV25
System: 405/625 Line Colour
Original List Price : £377 gns
V200 PL802 Luminance output
V301 ECC82 Frame Oscillator
V302 PL508 Frame output
V303 PCF802 Line Oscillator & Reactor
V400 PY500 Efficiency diode
V401 PL509 Line output
V402 PD500 EHT Stabiliser
V403 GY501 25kV Rectifier
V600 PLC84 R-Y Amp & clamp
V601 PCL84 B-Y Amp & clamp
V602 PCL84 G-Y Amp & clamp
CRT: A63 11X
Dual standard television incorporating 11 valves, 35 transistors, 40 diodes and providing the following:-
Colour and Monochrome on the 625-line system on U.H.F channels 21 – 68 inclusive and V.H.F. Channels C – H inclusive and suitable for colour modulation to the PAL system. In addition monochrome on V.H.F. channels 1 – 13 inclusive in bands 1 and 3 operating on the 405-line system. The set is provided with a multi-band tuner controlled by a six push button channel selector mechanism which also selects the transmission standard appropriate to the desired channel. The tuner however, has the attribute, ” any button, any channel, any system”.
Powered on, I cannot get a good locked colour. When fine tuning to the testcard I can get a good B&W picture, but tuning to tune it for colour sync and colour lock go out is impossible. Looks like it might have decoder issues/ref osc.
To get to the bottom of colour issue I need to disable the colour killer to shed some light on the fault condition. Checking the manual I found the colour killer can be overridden by shorting D600. I fed in colour bars from the Philips 5515T, powered on and the truth be confirmed, the reference oscillator is off hence unlocked colour.
Now what’s needed is to follow the oscillator tuning procedure, this entails scoping pin 1 of the decoder and checking the waveform present matches the one in the manual. The amplitude needs to be 2V p-p. Then I need to connect the scope to the left hand of R658, then adjust L604 for maximum output which should be 6V. Again a sine waveform is given as an example. Fingers crossed this sorts it. Checked the waveform at pin 1 of the decoder, it looks correct and reads about 1.8V p-p, it should be 2V but I guess that’s close enough.
Next up is setting the tuning of the oscillator and peaking it to the stated 6V p-p unfortunately the colours are still unlocked need to put my thinking head on now, I wonder if I need to now perform Burst tuning followed by setting up the phase discriminator.
Checked the burst, it should be 30V p-p +/- 5V I have roughly 23V p-p again pretty much within spec. I will check the phase discriminator next.
Success, adjusting the phase via VR602 has given colour lock. I think I need to sort the delay as I have blinds. Still much improved on what I had.