JVC DD-9 A - Page 18

DD-9A/B/C/E/J/U
(7) High-frequency equalization level switching operation
With the set in the STOP mode, remove bias cut pin
(8) on the computer board. Press the START switch,
then confirm that the bit for H. EQ. switches.
Next, with the set in the REC PAUSE mode, confirm
that the head current changes step by step.
[12.5 KHz
Preset
-O----5-)-+10----6O----5-
Fig. 20
(8) Computer playback gain adjustment
(9
Using a 1 kHz reference playback tape with the set in
the STOP mode, push up the AR switch and press the
START switch. Then, release the AR switch after
confirming that the set has begun the test program.
Next, remove post pin on the computer board.
After confirming that the output level at LINE OUT
is —4 dB, connect post pin Q) as before, connect an
electronic voltmeter to tab [55] on the computer
board, then adjust VRAO3 and VRBO3 on the main
amplifier board so that the output level is —10.5 dB.
The output at R channel goes OFF, when the MONI-
TOR switch is ON and the output at L channel is
OFF,
Record/playback check in computer switching oper-
ation
Remove post pin (9) on the computer board, apply
a singal of —20 dB to LINE IN and select a suitable
test program.
Next, press the START switch after stopping the
input at each operation, then change the REC mode
to the PLAY mode.
Enter a frequency corresponding to each test pro-
gram, then check the output. (Set the Dolby C NR
switches to OFF and use the normal UD tape.)
@ Explanation of diagrams
Fig. 21: BIAS: 8.3 kHz, —20 dB
Fig. 22: SENS (sensitivity): 1.0 kHz, -20 dB
Fig. 23: M. EQ. (medium-frequency equalization
level): 4.0 kHz, —20 dB
Fig. 24: H. EQ. (high-frequency equalization level):
12.5 kHz, —20 dB
No. 4198
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