THORN 3000 CHASSIS

The height has been slowly decreasing recently, and full
height can now be obtained only by adjusting the two
linearity controls. This of course affects the top and bottom
linearity, while there’s still some foldover at the bottom of
the raster. Would you suggest replacing the BD116 field
output transistor?
The field output transistor could be responsible, but if the
linearity is unaffected by the fault we suggest replacing the
two field charging capacitors C427/8. Also check that the
supply to the field output stage is correct – about 40V
across the decoupling electrolytic C432, which should be
checked by substitution if necessary. If the fault persists, it
would be best to check the voltages and waveforms in the
field driver and output stages as given in the manual.