Sharp VC-780E Service Manual page 39

VC-780E
VC-790ET
Probable causes and countermeasures
* Check if there is chroma signal at pin 30 of !C501.
* APC is misadjusted (R506). It is not allowed 10
readjust them, this means that !C501 is detective.
* Check if 1C501 is normally functioning.
[
No colour appears. (PAL / MESECAM)
Make sure "NTSC 3.58 H" signal at pin 11 of K502
is at "H" level.
* Put the unit in playback mode and check if the
chroma signal is given out at pin 30 of IC5701.
* Check if APC (R5812) has been properly adjusted.
(If no adjustment is effective, the IC itself is
defective.)
* Check if the "ROTATION" pulse is put in to pin 5
of 1€5701. (If the output from the system
controller does not reach this ie the 1C5701 or
1€501 is defective.)
* Be sure that the voltage at each pin of 1C5701 is as
specified.
No colour appears in NTSC 3.58
* Check if the chroma signal is applied at TP5702.
* Check if the gate (R5814 and R5815) has been
properly adjusted.
* Be sure that the voltage at each pin of 1C5702 is as
specified.
No colour appears in SECAM mode.
* Put the unit in playback mode in NTSC mode and
make sure pins 6 and 10 of K401 are at 9V level.
Readjust the flicker control (R440).
With the unit in playback mode in NTSC mode,
check if the video signal is given out to the
emitter of Q4405.
* Then make sure the video signal is given out to
pin 12 of 1C4401.
* Finally make sure the 17-MHz clock waveform
signal is put in to pin 9 of 1C4401.
No picture appears over the screen in
still/slow mode or no lateral stripes
in SP search mode in NTSC 3.58/4.43
mode.
—
Excessive skew is found in SP search
mode in NTSC 3.58/4.43 mode.
The image above and
below the noise bars is
seen skew as sketched
here.
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