JVC HR-XVC28BUC, Service Manual

Page: 18 / 149

1-18 (No.YD052)
4.3 Electrical adjustment (VHS SECTION)
Note:
The following adjustment procedures are not only necessary
after replacement of consumable mechanical parts or board
assemblies, but are also provided as references to be referred
to when servicing the electrical circuitry.
In case of trouble with the electrical circuitry, always begin a
service by identifying the defective points by using the measur-
ing instruments as described in the following electrical adjust-
ment procedures. After this, proceed to the repair,
replacement and/or adjustment. If the required measuring in-
struments are not available in the field, do not change the ad-
justment parts (variable resistor, etc.) carelessly.
4.3.1 Servo circuit
4.3.1.1 Switching point
(1) Play back the signal (A1) of the alignment tape (A2).
(2) Apply the external trigger signal to D.FF (E) to observe the
VIDEO OUT waveform and V.PB FM waveform at the
measuring points (D1) and (D2).
(3) Set the VCR to the manual tracking mode.
(4) Adjust tracking so that the V.PB FM waveform becomes
maximum.
(5) Set the VCR to the Auto adjust mode by transmitting the
code (F) from the Jig RCU. When the VCR enters the stop
mode, the adjustment is completed.
(6) If the VCR enters the eject mode, repeat steps (1) to (5)
again.
(7) Play back the alignment tape (A2) again, confirm that the
switching point is the specified value (G).
Fig.4-3a Switching point
4.3.1.2 Slow tracking preset
(1) Record the signal (A2) in the mode (B1), and play back
the recorded signal.
(2) Set the VCR to the manual tracking mode.
(3) Set the VCR to the FWD slow (+1/6x) mode.
(4) Transmit the code (F) from the Jig RCU to adjust so that the
noise bar becomes the specified value (G) on the TV
monitor in the slow mode.
(5) Set the VCR to the Stop mode.
(6) Confirm that the noise bar is (G) on the TV monitor in the
slow mode.
(7) Repeat steps (3) to (6) in the REV slow (+1/6x) mode.
(8) Repeat steps (1) to (7) in the mode (B2).
Note:
• For FWD slow (+1/6x) playback, transmit the code "43-
08" from the Jig RCU to enter the slow playback mode,
and transmit the code "43-D0" for REV slow (-1/6x)
mode.
Signal (A1)
(A2)
• Stairstep signal
• Alignment tape(EP,stairstep,NTSC) [MHP-L]
Mode (B) • PB
Equipment (C) • Oscilloscope
Measuring point (D) • VIDEO OUT terminal (75 ohm terminated)
• TP106 (PB. FM)
External trigger (E) • TP111 (D.FF)
Adjustment part (F) • Jig RCU: Code “ 43-5A ”
Specified value (G) • 6.5 ± 0.5H
Adjustment tool (H) • Jig RCU [PTU94023B]
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Signal (A1)
(A2)
• Ext. input
• Color (colour) bar signal [NTSC]
Mode (B1)
(B2)
• VHS SP
• VHS EP
Measuring point (D) • TV-Monitor
Adjustment part (F) • Jig RCU: Code “ 43-71 ” or “ 43-72 ”
Specified value (G) • minimum noise
Adjustment tool (H) • Jig RCU [PTU94023B]