THORN 3000 CHASSIS

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The picture on this set will suddenly change from perfect to
one which lacks contrast and has faded colours. This condidon will persist for a number of days, then a perfect picture will suddenly reappear. All the adjustments seem to work
normally.
Since the fault affects both the contrast and the colour, it
would seem to be in the i.f. strip. Check the a.g.c. and the i.f.
circuits carefully for dry -joints or similar troubles. Then
suspect the a.g.c. smoothing capacitors C179 (10µF) and
C134 (25µF, early production only), and the first i.f.
amplifier transistor’s collector decoupling electrolytic C177
(30µF), also the vision i.f. transistors, especially the final
one VT104.

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