JVC AX-UXG6, Service Manual

Page: 57 / 108

2-41
UX-G6/FS-G6
Procedures for adjusting the electrical circuit
The following adjustments should be performed after adjusting the tape traveling and head angles.
• The sequence of adjustment should in principle be according to the following order of description.
• The adjustment items denoted by asterisk should be performed whenever the head has been changed.
Items Adjusting position Reference value Remarks
Adjusting
position
[0dBs = 0.775V]
Items Adjusting and confirmation methods frequency level deviation of output up and down values
Confirmation
of Dolby circuit
recording
(Recording
mode)
Recording
Dolby B 1kHz Cal-40dB
5kHz Cal-20dB
1kHz Cal 0dB
+5.7dB 2dB
+3.5dB 1.5dB
0dB +0.5/-1 dB
Frequency level
Deviation of output up
and down values
Input:[Line IN] (-8dBs)
Measuring points:Pin 8 of IC635
and pin 2 of CN641
Reference level at measuring
points 400Hz
-8dBs (=Cal. level)
Adjustment of
playing level
Adjustment of
playing
equalizer
Reference
value of
recording
input
Adjustment of
bias frequency
Adjustment of
recording and
playing
frequency
characteristics
While playing the test tape
VT724 (1kHz), adjust the
CN641 output to -25.5dBs with
VR611 and VR621.
(The L - R channel output
difference should be within
0.5dB).
While playing the test tape
TMT7063 (1kHz and 12.5kHz),
adjust the test point TP (CN641)
output to the reference values at
1kHz and 12.5kHz outputs with
VR612 (Lch) and VR622 (Rch).
Confirm that the input level at
the test point TP (CN641)
terminal is -25.5dB when
1kHz -28.2dBs has been
applied to the line input.
Connect the frequency counter
to the test points TP631 and
TP632 and adjust the bias
frequency to 100kHz with
Record 1kHz/12.5kHz with a
normal tape, and adjust the
deviation at 12.5kHz to +0
0.5dB with reference to 1kHz
by means of VR613 (Lch) and
VR623 (Rch).
*2
*3
4
5
*6
L:VR611
R:VR621
L:VR612
R:VR622
L6351
L:VR613
R:VR623
-25.5dBs
0.5dB
(L-R difference:
within 0.5dB)
With reference
to 1kHz, the
deviation of
12.5kHz
should be 1.5
0.5dB
Output level:
-25.5dBs 1dB
9kHz
-1kHz
Normal tape:
0 0.5dB
Chrome tape:
0 4dB
Adjust the playing level since
this level will be changed
whenever the head has been
changed.
At this time, the impedance of
electronic voltmeter should be
100 or more.
NR : OFF
By using the test tape
TMT7063 (12.5/1kHz/63Hz),
confirm that 63Hz:+2dB 3dB
with reference to 1kHz.
Tape : chrome
Mode : recording
Ref-20dB : [Value reduced by
as much as -20dB from the
reference input value] 28.2dB
The bias value in the case of
chromium tape will be set by
shifting the voltage with
reference to that in the case of
normal tape.
Unless the bias current has
been adjusted correctly, the
recording characteristics will
become as indicated in the
diagram on the left hand side.
Response (dB)
High frequency area up
High frequency area down
Bias current is smaller.
Bias current is appropriate.
Bias current is greater.
Frequency
0
50Hz 1kHz 12.5kHz
1