Electrical Adjustment Instructions; Test Equipment Required; Head Switching Position Adjustment - Hitachi VT-FX795A Service Manual

4-3 ELECTRICAL ADJUSTMENT INSTRUCTIONS

General Note: "CBA" is an abbreviation for
"Circuit Board Assembly."
NOTE:
1.Electrical adjustments are required after replacing
circuit components and certain mechanical parts.
It is important to do these adjustments only after
all repairs and replacements have been com-
pleted. Also, do not attempt these adjustments
unless the proper equipment is available.
2.To perform these alignment / confirmation proce-
dures, make sure that the tracking control is set in
the center position: Press either "CHANNEL L5 ? ? " or
"CHANNEL K" button on the front panel first, then
the "PLAY" button on the front panel.

4-3-1 Test Equipment Required

1.Oscilloscope: Dual-trace with 10:1 probe,
V-Range: 0.001~50V/Div.,
F-Range: DC~AC-20MHz
2.Alignment Tape (MH-1)
4-3-2 Head Switching Position
Adjustment
Purpose:
To determine the Head Switching point during
playback.
Symptom of Misadjustment:
May cause Head Switching noise or vertical jitter
in the picture.
Test point Adj.Point
TP751(V-OUT) VR501
TP302(RF-SW) (Switching Point)
J20(GND) (MAIN CBA)
Measurement
Tape
Equipment
MH-1 Oscilloscope
Connections of Measurement Equipment
TP751(V-OUT)
Main
J20(GND)
CBA
TP302(RF-SW)
Reference Notes:
Playback the Alignment tape and adjust VR501 so that
the V-sync front edge of the CH1 video output wave-
form is at the 6.5H(412.7µs) delayed position from the
rising edge of the CH2 head switching pulse wave-
form.
Mode Input
PLAY
-----
(SP)
Spec.
6.5H±1H
(412.7µs±60µs)
Oscilloscope
CH1 CH2
Trig. (+)
Figure 1
EXT. Syncronize Trigger Point
CH1
1.0H
6.5H
CH2
Switching Pulse
0.5H
V-Sync
4-3