JVC DD-9 A - Adjustment Procedures; Computer clock adjustment; Computer preset check; A;D adjustment

= Adjustment procedures
(1) Computer clock adjustment
Connect a counter to ICGO2 P1 (TP CLOCK), then
turn the core of TGQ3 so that the oscillation frequen-
cy becomes 400 kHz. (In this case, connect a 1 MQ
resistor in series with the counter input.)
(2) Computer preset check
At each tape position, confirm that each bit is equal
to the pertinent value in the table below.
Medium- High-frequency
Bias |Sensitivity| frequency | equalization at
equalization L/R
Normal] 14 7 3 4
FeCr 14 8 3 5
Metal 9 8 4 11
CrO2 14 7 3 5
|
Notes: @ Concerning the FeCr position, set the TAPE
SELECT switch to CrO2 with Normal or FeCr
tape.
® Concerning the CrO2 position, set the TAPE
SELECT switch to CrO2 with CrO2 tape.
(3) Computer oscillation adjustment
When pressing the START switch with the set (DD-9)
in the STOP mode, the oscillation switching program
starts.
The
START
switch
not
pressing,
signals
are
repeatedly
emitted in the order of 1kHz — 4kHz — 8kHz —
12.5 kHz — 1 kHz at intervals of about 1.5 sec.
Connect an electronic voltmeter to tab 55 (A/D IN)
on thecomputer board, adjust the oscillation level for
each frequency by the pertinent half-fixed resistor.
Frequency | Half-fixed resistor | Adjustment value
1.0kHz VRGO4 —27 dB
4.0 kHz VRGO3 —28 dB
8.3 kHz VRGO2 —27 dB
12.5kHz VRGO1 —25 dB
Note:When pressing the START switch in arbitrary
output mode, it is possible to keep this output
mode.
(4) A/D adjustment
With the START switch pressed and the set in the
STOP mode, confirm that the A/D counter operates.
Next, connect an oscilloscope (DC couple) to the
A/D test point, then confirm that the waveform
shownat right appears.
Adjust VRGO5 so that the indication of the A/D
counter is 64.
When releasing the START switch, the sensitivity
switching operation is performed.
DD-9A/B/C/E/J/U
2.2V
Ov
About 24 msec About 40 msec
Fig. 17
(5) Sensitivity and medium-frequency equalization level
switching operation
When releasing the START switch after A/D adjust-
ment, confirm that the bit for SENS, switches.
Next, confirm that the bit for M. EQ switches, remove
post pin and connect an electronic voltmeter to
tabs and . Then, confirm that the output
changes step by step.
SENS M. EQ
1 kHz 4 kHz
(5 O00 7 1B Oe
Fig. 18
(6
Bias adjustment
Press the START switch with the set in the STOP
mode, then confirm that the bit for BIAS switches
from 15 through 0.
Next, put the set into the REC PAUSE mode, then
confirm that the record head current changes step
by step.
Fig. 19
Note: Set the bias for metal tapes (adjust VRGO6) and
adjust the oscillation frequency.
@ Adjust VRGO6 so that emitter voltage of
XG04 becomes 10.6 V.
@ Adjust TGO1 so that bias frequency becomes
95 kHz.
@ Adjust TGO2 so that bias tuning becomes
peak point.
No. 4198