Electrical Adjustment; Servo Circuit; Switching Point - JVC HR-J691U Service Manual

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 (EP,stairstep,NTSC) [MHP-L]
Mode (B) • PB
Equipment (C) • Oscilloscope
Measuring point (D1) • VIDEO OUT terminal (75Ø terminated)
(D2) • TP106 (PB. FM)
External trigger (E) • TP111 (D.FF)
Adjustment part (F) • R4028
Specified value (G) • 6.5 ± 0.5H
(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) Adjust the adjustment point (F) so that the value of the
switching point becomes identical to the adjustment value
(G).
Trigger point
Switching point
Fig. 3-3-1-1a
3-4
V.sync
V. rate
Switching point