Where only one color is showing, suspect an incorrectly adjusted individual
background/bias control or bad part on the CRT neck board for that color.
|NotTaR of Television Sets : Red, green, or blue retrace lines
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<< White/gray retrace lines |
| Bad CRT causing retrace l.. >>
- Individual brightness/background/bias control(s) - mark setting of pot for
the problem color and then see if a slight adjustment removes the retrace
lines. See the chapter: "TV Adjustments". Of course, if this happened
suddenly, the problem is not due to a misadjusted control though a dirty
pot is possible - turn it back and forth - this might clean it and restore
- Component or connection on CRT neck board - insufficient voltage to or
incorrect biasing of the video driver for this color can result in the
CRT never totally blanking. Compare voltages and signals, and swap
components between good and bad channels to confirm.
- Blanking circuit - this may be a part of the video/chroma chip or separate.
Check and compare waveforms of good and bad colors to determine if the
blanking pulses are making it to the video output.
There is a slight possibility that a bad CRT may result in visible retrace
lines. To eliminate this possibility:
- Disconnect the filament - all evidence of a picture, raster, and retrace
lines should disappear once the filaments/cathodes have cooled (15 seconds
or so. If there are still visible retrace lines, the CRT is suffering
from cold or field emission from someplace (may not even be the cathode).
- Turn down the screen (G2) control on the flyback (usually). If one color
remains no matter how you set the control, again there is some kind of
weird emission from the CRT. However, if white/gray retrace lines remain,
the problem may be in the screen supply.
See the section: Bad CRT causing retrace lines.
<<White/gray retrace lines |
| Bad CRT causing retrace l..>>