JVC CA-UXB70 Service Manual page 36

4.2.2 Check and adjustment of the Head amplifier section
Item
1. Head azimuth
adjustment
2. Tape speed
adjustment
(Reference value)
Speed difference
between the
normal and
reverse directions
Wow and flutter
3. Recording /
playback
frequency
characteristic
adjustment
(Reference value)
Recording bias
frequency
(Reference value)
Erasing current
1-36 (No.MB013)
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Check/Adjustment Method
1) Play back the end part of the test tape VT703 (10 kHz).
2) Adjust the head azimuth screws so that the output becomes
maximum in both the normal and reverse directions. After
adjustment, lock the screws with screw bond without fail.
Measuring output terminal: Speaker terminal, 4 load resistance
Difference between L-ch and R-ch: Within 3 dB
Difference between FWD and REV directions: Within 4 dB
Adjust max level in FWD and REV. After adjusting, should be
Applied bond (THREEBOND 1401 A/C) to screw.
Azimuth screw
Screw for
REV
Neji Lock
1) Play back the end part of the test tape VT712 (3 kHz).
2) Adjust VR37 so that the frequency counter reads 3000
in playback in the normal direction.
Measuring output terminal: Speaker terminal
Make sure that speed difference between the normal and
reverse directions is 60 Hz or less by reading of the frequency
counter. (With the beginning part of the test tape)
Play back the end part of the test tape VT712 (3 kHz).
Make sure that the wow and flutter meter reads 0.25 % (WRMS)
or less.
1) Set a blank cassette tape (Type I: AC225) and enter the set into
the recording pause mode.
2) Cancel the pause mode and start recording. Repeat to input the
1 kHz and 10 kHz reference signals alternately from the CD test
disk to record the signals on the blank tape.
3) While playing back the repeatedly input 1 kHz and 10 kHz
reference signals, adjust VR31 so that output level of 10 kHz
signals is +2 dB 1 dB of 1 kHz.
1) Set a blank cassette tape (Type I: AC225) and enter the set into
the recording pause mode.
2) Make sure that the bias frequency at the bias test point (Refer on
1-25 board drowing) on the head amplifier board is 70
1) Set a blank cassette tape (Type I: AC225) and enter the set into
the recording pause mode.
2) After connecting a 1 resistor to the erasing head in series,
cancel the pause mode and start recording. Connect the
electronic voltmeter to both the terminals and measure the
erasing current.
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Adjusting
Point
Head
azimuth
screw
phase
(0 )
Azimuth
for FWD
Neji Lock
15 Hz VR37
VR31
-1dB
70
9 kHz.
Standard
Value
Maximum
output
(45 )
3000 15Hz
60 Hz or less
0.25 %
(WRMS) or
less
1dB
9kHz
Erasing
current: 60
mA (Type I
tape)