Mechanism Compatibility Adjustment; Tension Pole Position; Fm Waveform Linearity - JVC HR-J691U Service Manual

3.2 Mechanism compatibility adjustment

Notes:
• Although compatibility adjustment is very important, it is not
necessary to perform this as part of the normal servicing
work. It will be required when you have replaced the A/C head,
drum assembly or any part of the tape transport system.
• To prevent damaging the alignment tape in the compatibility
adjustment, prepare a cassette tape (for self-recording/play-
back), perform a test on it by transporting it and making sure
that the tape is not bent by the tape transport mechanisms
such as in the guide rollers.(See Fig.3-2-2a)

3.2.1 Tension pole position

Notes:
• This adjustment must be performed every time the tension
band is replaced.
•
Signal (A) Back tension cassette gauge
[PUJ48076-2]
•
Mode (B1) Play back position
•
(B2) Eject end
•
Adjustment part (F) Adjust pin [Mechansim assembly]
25 - 51 gf•cm (2.45 – 5 × 10
•
Specified value (G)
(1) Play back the back tension cassette gauge (A).
(2) Check that the indicated value on the left side gauge is within the speci-
fied value (G).
(3) If the indicated value is not within the specified value (G), perform the
adjustment in a following procedure.(See Fig.3-2-1a)
1) Remove the top frame, cassette holder and side frames (L/R) all
together. (See "Mechanism Assembly and Disassembly".)
2) Rotate the loading motor gear to move the control plate so that the
triangular stamping to the left of the "P" stamping is aligned with the
stamping (a) on the main deck. This positioning is mode (B1).
3) Adjust by turning the adjustment pin so that the tip of the tension
arm is aligned with the stamping (b) on the main deck.
4) Rotate the reel disk (S) by about one turn clockwise and make sure
that the round hole of the adjustment pin is located in the "OK" range.
If it is outside this range, restart the adjustment from the beginning.
After completion of the adjustment, rotate the loading gear motor to re-
turn it to the mode (B2) position.
TENSION ARM
Stamping(b)
OK
NG
ADJUST PIN
Fig. 3-2-1a

3.2.2 FM waveform linearity

•
Signal (A1) Alignment tape(SP, stairstep, NTSC) [MHP]
•
(A2) Alignment tape(EP, stairstep, NTSC) [MHP-L]
•
Mode (B) PB
•
Equipment (C) Oscilloscope
•
Measuring point (D) TP106 (PB. FM)
•
External trigger (E) TP111 (D.FF)
•
Adjustment part (F) Guide roller [Mechanism assembly]
•
Specified value (G) Flat V.PB FM waveform
•
Adjustment tool (H) Roller driver [PTU94002]
3-2
Nm]
-3
CONTROL PLATE
Stamping(a)
Switching point
(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) Make sure that there is no significant level drop of the V.PB
FM waveform caused by the tracking operation, with its
generally parallel and linear variation ensured. Perform the
following adjustments when required. (See Fig. 3-2-2b.)
(5) Reduce the V.PB FM waveform by the tracking opera-
tion. If a drop in level is found on the left side, turn the
guide roller of the pole base assembly (supply side) with
the roller driver to make the V.PB FM waveform linear.
If a drop in level is on the right side, likewise turn the guide
roller of the pole base assembly (take-up side) with the
roller driver to make it linear. (See Fig. 3-2-2b.)
(6) Make sure that the V.PB FM waveform varies in parallel
and linearly with the tracking operation again. When re-
quired, perform fine-adjustment of the guide roller of the
pole base assembly (supply or take-up side).
(7) Unload the cassette tape once, play back the alignment
tape (A1) again and confirm the V.PB FM waveform.
(8) After adjustment, confirm that the tape wrinkling does not
occur at the roller upper or lower limits. (See Fig. 3-2-2a.)
[Perform adjustment step (9) only for the models
equipped with SP mode and EP (or LP) mode.]
(9) Repeat steps (1) to (8) by using the alignment tape (A2).
Improper
(a) GUIDE ROLLER
(b) GUIDE POLE
Fig. 3-2-2a
• Proper waveform variation
• Improper waveform variation
Up
B
A
C D
Fig. 3-2-2b
Proper
Down
Roller driver
Guide roller
(supply side)