THORN 2000 CHASSIS
When this set comes on the picture and sound are good. It
takes up to half an hour for this to happen however, and
afterwards it sometimes goes off again for a second, leaving
a dim raster. The picture and sound come on gradually. The
picture appears in monochrome at first, then the colour
gradually comes up. The signals always return gradually
following the occasional dim raster.
As all signals are involved it seems that either a supply
line is going intermittent (monitor the 30V lines with a meter
during the fault) or there’s a fault in the i.f. or a.g.c. sections
of the set. For the latter possibility, start by checking the
voltage across the a.g.c. decoupler C56 in the i.f. strip. This
should be about 12-14V with a strong signal. If the a.g.c.
line is working correctly, check voltages in the i.f. strip. If
not, check back to the a.g.c. stages VT9/10: the
electrolytics C54/5 (both 50µF) could be playing up.