I inherited a Toshiba model CF2750K, chassis# TAC 9011, with the notorious vertical
problem...compressed to center and upper half...bottom half dark. After reading some
of the posted hints, I arbitrarily replaced the 1uf-50v capcitor in the verical section.
It seemed to be the only 1uf in the vertical section, but it was C-305 rather than
the C-301 or C-342 mentioned by others. One mentioned that the quality of the capacitor
was important, so I replaced it with a paper-tubular (mylar?) 1uf-200v. But apparently,
the set may have had two defects, because when I turned it on, it now had no vertical
deflection at all (bright horizontal white line in middle). I believe the handling of
the PC-board had caused a lingering problem to appear. I arbitarily re-soldered the
seven in-line pins on IC-301 which I believe is probably the Vertical power IC. It
had a large heat-sink.
The set now worked about normally, except that the vertical linearity was a little
disappointing...a slight widening of spacing progressing from bottom toward top, with
and exaggerated widening on the top inch of the screen. I could only find one pot named
vertical height, but could find nothing for vertical linearity. There were other
un-named pots in another section but did not to turn them, and they were sealed. They
did not have the expected 300 series number.
I did shunt an extra 660uf across an existing 2200uf (300 series) and shunted an
extra 25uf across an existing 10uf (300 series)...both in the vertical section.
Adding these made no significant improvement. Incidentally, capacitors of about 3/8"
diameter can be tack-soldered on the bottom side (just enough space) without removing
the original (electrolytics almost never short).
Does anyone have any hints as to improving the vertical linearity on this model?Is it
possible that the high quality of my 1uf capacitor was TOO high? (one poster suggested
that the circuit was very critical to the quality of the 1uf capacitor)