JVC HR-XVC28BUS Service Manual page 16

4.2 Mechanism compatibility adjustment (VHS SECTION)
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 re-
placed the A/C head, drum assembly or any part of the
tape transport system.
• To prevent damaging the alignment tape in the compat-
ibility adjustment, prepare a cassette tape (for self-re-
cording/playback), 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.4-2b.)
4.2.1 Tension pole position
Notes:
• This adjustment must be performed every time the ten-
sion band is replaced.
Signal (A) • Back tension cassette gauge [PUJ48076-2]
Mode (B1) • PB
(B2) • Eject end
Adjustment part (F) • Adjust pin [Mechansim assembly]
Specified value (G) •
25 - 51 gf•cm (2.45 - 5 x 10
(1) Play back the back tension cassette gauge (A).
(2) Check that the indicated value on the left side gauge is
within the specified value (G).
(3) If the indicated value is not within the specified value (G),
perform the adjustment in a following procedure.(See
Fig.4-2a.)
a) Remove the top frame, cassette holder and side
frames (L/R) all together. (Refer to the SERVICE
MANUAL No.86700 [MECHANISM ASSEMBLY].)
b) 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).
c) Adjust by turning the adjustment pin so that the tip of
the tension arm is aligned with the stamping (b) on
the main deck.
d) 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 return it to the mode (B2) position.
TENSION ARM
Stamping(b)
OK
NG
ADJUST PIN
Fig.4-2a
1-16 (No.YD052)
4.2.2 FM waveform linearity
Signal
Mode
Equipment
Measuring point (D)
External trigger (E)
Adjustment part (F)
Specified value (G)
Adjustment tool (H)
(1) Play back the alignment tape (A1).
(2) Apply the external trigger signal to D.FF (E), to observe
(3) Set the VCR to the manual tracking mode.
(4) Make sure that there is no significant level drop of the V.PB
(5) Reduce the V.PB FM waveform by the tracking operation.
-3
Nm)
(6) Make sure that the V.PB FM waveform varies in parallel
(7) Unload the cassette tape once, play back the alignment
(8) After adjustment, confirm that the tape wrinkling does not
(9) Repeat steps (1) to (8) by using the alignment tape (A2).
CONTROL PLATE
Stamping(a)
(A1) • Alignment tape(SP, stairstep, NTSC) [MHP]
(A2) • Alignment tape(EP,stairstep,NTSC) [MHP-L]
(B) • PB
(C) • Oscilloscope
• TP106 (PB. FM)
• TP111 (D.FF)
• Guide roller [Mechanism assembly]
• Flat V.PB FM waveform
• Roller driver [PTU94002]
the V.PB FM waveform at the measuring point (D).
FM waveform caused by the tracking operation, with its
generally parallel and linear variation ensured. Perform the
following adjustments when required. (See Fig. 4-2c.)
If a drop in level is found on the left side, turn the guide roll-
er 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. 4-2c.)
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).
tape (A1) again and confirm the V.PB FM waveform.
occur at the roller upper or lower limits. (See Fig. 4-2b.)
[Perform adjustment step (9) only for the models equipped
with SP mode and EP (or LP) mode.]
[Perform adjustment step (9) only for the models
equipped with SP mode and EP (or LP) mode.]
Improper
(a) GUIDE ROLLER
(b) GUIDE POLE
Fig.4-2b
Proper