Position Adjustments - JVC BR-S822U Service Training

playback of a pre-recorded signal
for true reproduction of luminance
and color.
This relationship won't be
maintained, however, if the correct
orientation of the upper drum is
not maintained during the installa-
tion. Incorrect tracks will be
scanned during the playback if the
Orientation ts not correct. This can
be corrected by readjusting the
control head or tracking control,
but color rotation will be incorrect.
This results in loss of color when a
pre-recorded tape is played back.
This incorrect phase relationship
will be maintained when a record-
ing 1s made using the incorrectly
installed upper drum. So while it
would be possible to reproduce the
color signal from a tape recorded
on that particular machine, color
interchangeability with another
VHS machine would not be
possible. This 1s a common
mistake seen during the installa-
tion of an upper drum. Refer to the
service manual for the correct
orientation of the upper drum
before installing.
Position Adjustments
Centering of the upper drum 1s
another factcr to be considered
while installing a new upper drum.
Recent products have a very tight
tolerance. Intolerable eccentricity
could result in an unstable video
picture and distorted audio.
The height of the video head
chip pair from the rabbet decides
which track is being scanned when
the corresponding control pulse is
picked up by the Audio Control
head. This might vary due to
manufacturing tolerances. Audio
and control pulses are recorded
and played back using the same
head assembly. It is necessary to
keep this relationship so as to
maintain audio and video synchro-
Over Scan
CH 1FM
CH 2FM
CH 1
O o
CR 2
ae
Head switching adjustment
PB FM
Figure 5
nization, and achieve maximum
picture clarity at the center posi-
tion of the manual tracking con-
trol. Mechanical position adjust-
ment of the AC head is described
in the service manual for this
purpose. This adjustment is also
known as the X-position or
X-value adjustment. Standard test
tapes such as the MHP-X tape are
available for this adjustment.
Head Switching
The recorded video tracks on
the tape are discontinuous. It is
necessary to switch from one head
to the other one at the end of each
scan. A slight margin of over-
scanning in VHS allows the
switching point to be changed by a
couple of horizontal TV lines. This
switching point is standardized so
that the switching occurs before
the V-Sync. It is necessary to
pertorm the switching point
adjustment precisely after replac-
ing an upper drum. An incorrect
switching point could cause
unstable video, distorted video,
and distorted Hi-Fi audio. Follow
the directions in your service
manual to perform this adjustment
(see Fig;'5),
And finally, it is also neces-
sary to check and or adjust the
recording level and frequency
response of the luminance and
color signals after performing the
tracking preset, X-value, and
playback switching point adjust-
ments.
BR-S822 Course
Appendix
page 19