Sharp VT-3418X, Service Manual, Page: 41 / 170

ADJUSTMENT OF THE
VCR ELECTRICAL CIRCUITRY
Notes:
Before the adjustment:
Electrical adjustments discussed here are often required after replacement of electronic
mechanical parts such as video heads.
Check that the mechanism and all electric components are in good working condition prior to the
adjustments, otherwise adjustments can not be completed.
l Instruments required:
signal generator
e oscilloscope
Frequency counter
Blank video cassette tape
Screwdriver for adjustment
bar generator
voltmeter
@Alignment tape
Extension connector
AL AL)
n
SERVO CIRCUIT ADJUSTMENT
Adjustment of head switching point
Measuring Dual-trace oscilloscope
instrument
Mode
Cassette
Test point
Playback
Alignment tape
VIDEO OUT (pin of EL
connector) to 1
(Trigger) to
(Located on the Y/C
Control
head switching point
adjustment control
Specification
H (lines)
Play the alignment
Short circuit test points
and on
the A/V Jack or remove the cassette
housing to set the auto tracking to center.
(See Note below)
Connect a dual trace oscilloscope to the VIDEO
OUT (pin of EL connector) and
(Trigger the oscilloscope with the head
switching pulse on
Adjust so that the leading edge of the
head switching pulse is (lines) ahead of the
vertical sync as shown in Figure
1
HEAD .
SWITCHING
P U L S E
(lines)
V-sync.
Figure
Notes:
To make this adjustment, disable the AUTO
TRACKING function.
The AUTO TRACKING function is disabled in the
following cases.
(In the playback mode only.)
the cassette housing control is
removed, press both tracking control buttons of
the remote control unit at the same time to set
the tracking in center.
When test points and on the A/V
jack are short-circuited.