Compatibility Adjustment - JVC HM-DH40000K Service Manual

3.3 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 re-
placed the A/C head, drum assembly or any part of the
tape transport system.
• To avoid any damage to the alignment tape while per-
forming the compatibility adjustment, get a separate
cassette tape (for recording and play back) ready to be
used for checking the initial tape running behavior.
• Unless otherwise specified, all measuring points and
adjustment parts are located on the Main board.
• When using the Jig RCU, it is required to set the VCR to
the Jig RCU mode (the mode in which codes from the
Jig RCU can be received). (See SECTION 2 SPECIFIC
SERVICE INSTRUCTIONS.)
Jig RCU
[Data transmitting method]
Depress the " " ( 3 ) button
after the data code is set.
CUSTOM CODE
43: A
53: B
DATA CODE
Fig.3-3a Jig RCU [PTU94023B]
3.3.1 Tension pole position
Signal (A) • Back tension cassette gauge [PUJ48076-2]
Mode (B) • PB
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.
a) Set the VCR to the mechanism service mode. (See
SECTION 2 SPECIFIC SERVICE INSTRUCTIONS.)
b) Set the VCR to the play back mode and adjust by
turning adjustment pin to align the tension arm as-
sembly edge with the main deck hole (A) on the right
edge marker. (See Fig. 3-3-1a.)
Tension arm
assembly
Edge
Hole (A)
Marker
0.5 mm
Tension arm assembly
Tension brake assembly
Fig.3-3-1a
1-28 (No.82933)
INITIAL MODE
CODE
CODE
-3
Nm]
Adjust pin
3.3.2 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]
(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. 3-3-2a.)
(5) Reduce the V.PB FM waveform by the tracking operation.
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 roll-
er driver to make it linear. (See Fig. 3-3-3a.)
(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. 3-3-2b.)
[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).
Proper waveform variation
Improper waveform variation
Up
A
C
Fig.3-3-2a
Down
B
Roller driver
Guide roller
D
(supply side)