HMV 2704

On switching the set on the picture is excessively bright so
that the brightness and contrast controls have to be turned
right back, giving a very washed out picture. After about
twenty minutes the picture goes very dark and after
resetting the brightness and contrast controls the picture is
perfect. The sound is unaffected and the picture remains
excellent for the rest of the evening after this initial
disturbance.
Check the beam limiter transistor VT901 and set up the
beam limiter and preset brightness controls as described in
the manual. If the problem persists, check the offset pulse
generator and adder transistors VT204 and VT205 on the
video board, and the associated 0A91 diodes W202/3.
(Thorn 3000 chassis.)