Hitachi VT-FX795A, Service Manual, Page: 21 / 69

4-3
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.
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(412.7
µ
s) delayed position from the
rising edge of the CH2 head switching pulse wave-
form.
Test point Adj.Point Mode Input
TP751(V-OUT)
TP302(RF-SW)
J20(GND)
VR501
(Switching Point)
(MAIN CBA)
PLAY
(SP)
-----
Tape
Measurement
Equipment
Spec.
MH-1 Oscilloscope
6.5H
±
1H
(412.7
µ
s
±
60
µ
s)
Connections of Measurement Equipment
Oscilloscope
Main
CBA
TP751(V-OUT)
CH1 CH2
Trig. (+)
J20(GND)
TP302(RF-SW)
Figure 1
EXT. Syncronize Trigger Point
1.0H
CH1
CH2
Switching Pulse
6.5H
V-Sync
0.5H