I'm working on a 1993 Sylvania (25S104 chassis) TV. It's picture is too
dark. The problem happened suddenly.

With either an RF or a composite signal, the picture appears very dark,
with red and blue highlights. With signal removed, picture is made up
of black and white dots, but there is no grey background. sound is OK,
horiz and vert size is OK. HV is around 27KV. Filament has 6 V.
Screen has about 385V.

In examining the schematic, I see a transistor labeled ABL. It connects
to the flyback and the (chroma, luma, sweep) chip. Is this some sort
of brightness limiter? On the schematic, it shows 17v on the base and
2.7v on the emitter. I only measure 4 v on the base. The emitter
voltage is OK. An Ohm check does not show the transistor to be shorted.
What could I check next?