A/C Head Phase(X-Value); Electrical Adjustment; Servo Circuit; Switching Point - JVC HR-S6950EU Service Manual

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3.2.4 A/C head phase (X-value)
•
Signal (A1) Alignment tape(SP, stairstep, PAL) [MHPE]
•
(A2) Alignment tape(LP, stairstep, PAL) [MHPE-L]
•
Mode (B) PB
•
Equipment (C) Oscilloscope
•
Measuring point (D) TP106 (PB. FM)
•
External trigger (E) TP111 (D.FF)
•
Adjustment part (F) A/C head base [Mechanism assembly]
•
Specified value (G) Maximum V.PB FM waveform
•
Adjustment tool (H) Roller driver [PTU94002]
(1) Play back the alignment tape (A1).
(2) Apply the external trigger signal to D.FF (E), to observe
the V.PB FM waveform at the measuring point (D).
(3) Set the VCR to the manual tracking mode.
(4) Loosen the screws (4) and (5), then set the Roller driver
to the innermost projected part of the A/C head. (See Fig.
3-2-4a.)
(5) Rotate the roller driver so that the A/C head comes clos-
est to the capstan. From there, move the A/C head back
gradually toward the drum until the point where the FM
waveform is maximized for the second time, and then
tighten the screws (4) and (5) temporarily.
(6) Play an alignment tape (A2) and set to the manual-track-
ing mode.
(7) Fine-adjust A/C head base position to maximize the FM
waveform, and then tighten the screws (4) and (5) firmly.
(8) Play alignment tapes (A1) and (A2) and confirm that the
FM waveforms are maximized when the tracking is at the
center position.
Roller driver
To the drum
Toward the capstan
Screw (4)
Head base
Toward the drum
A/C head
Screw (5)
To the capstan
Fig. 3-2-4a
Alignment tape
[SP, stairstep]
played with the
SP head
Drum side Control head position
Fig. 3-2-4b
3-4
Alignment tape
[EP(LP), stairstep]
played with the
EP(LP) head
X-value adjustment point
Capstan side
Maximum
Digitized in Heiloo Netherland
3.3

Electrical adjustment

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 re-
ferred 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 meas-
uring instruments as described in the following electrical ad-
justment procedures. After this, proceed to the repair, re-
placement and/or adjustment. If the required measuring in-
struments are not available in the field, do not change the
adjustment parts (variable resistor, etc.) carelessly.

3.3.1 Servo circuit

3.3.1.1 Switching point

Signal (A1) • Stairstep signal
(A2) • Alignment tape (LP, stairstep, PAL) [MHPE-L]
(A3) • Alignment tape (EP, stairstep, NTSC) [MHP-L]
Mode (B) • PB
• TBC:OFF
Equipment (C) • Oscilloscope
Measuring point (D1) • VIDEO OUT terminal (75Ø terminated)
(D2) • TP106 (PB. FM)
External trigger (E) • TP111 (D.FF)
Adjustment part (F) • Jig RCU: Code "5A"
(F1) • Jig RCU: Code "51" or "52"
Specified value (G) • 7.5 ±0.5 H
(G) • 8.0 ±0.5 H (PAL)
• 7.5 ±0.5 H (NTSC)
Adjustment tool (H) • Jig RCU [PTU94023B]
[For the model without TBC function]
(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 meas-
uring 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).
[For the model equipped with TBC function]
Steps (1) to (4) are the same as previous steps (1) to (4).
(5) Transmit the code (F1) from the Jig RCU to adjust so that the
trigger point of the VIDEO OUT waveform is changed from
the trailing edge of the V. sync signal becomes the specified
value (G1).
(6) Set the VCR to the stop mode or eject mode.
(7) Play back the signal (A1) of the alignment tape (A3).
(8) Repeat steps (2) to (6).
Trigger point
Switching point
Fig. 3-3-1-1a
V.sync
V. rate
Switching point
3/28/2017