JVC SR-VS30U Service Manual page 16

Item Conditions
6 Checking Measuring point:
recording Both ends of
bias current 100 ohm resistor
(Value connected to the
appearing R/P head terminal
here are
just for
reference
7
Input
sensitivity
level check
*8 REC/PB LINE INPUT level:
frequency Ref. -20 dB
response (-40 dBs
adjustment NR switch : OFF
Spec. of freq. area
250 Hz 1 Hz
3 dB
*9 REC/PB NR switch : Off
sensitivity TAPE switch :
adjustment Normal
LINE INPUT level:
Ref. -20 dB
1-16 (No.MB061)
Adjustment and Confirmation
Connect 100 ohm resistor to the R/P head in
series, and measure voltage at both ends of the
resistor to check to see if measured voltage
meets the following requirements on both
channels.
In recording with metal tape, the bias current
is 1150 uA (1.15 mA).
In recording with CrO
is 700 uA (0.7 mA).
In recording with normal tape, the bias current
is 590 uA (0.59 mA).
1.
Supply at 1kHz signal to the LINE IN terminals
at -19 dBs, confirm that LINE OUT level is -
8dBs.
2.
Confirm that difference level between left and
right within 2 dB.
This step must be performed after the slave
oscillation adjustment.
2 dB) Record the 1.25 kHz and 12.5 kHz signals at the
level of -20 dB (20 dB lower than the reference
level).
Playing back the recorded signals, adjust VR146
and VR246 so that the level of the 12.5 kHz
signal is 0 0.5 dB to the level of the 1.25 kHz.
10 Hz 12.5 Hz
Decrease in
high frequencies
5 dB
0 50 Hz
1. Apply 400 Hz signal to the LINE IN terminals,
record 400 Hz signal at -20 dB input for both
(L and R) channels on a normal tape.
2. While recording the recorded signal and play it
back, adjust VR126(L) and VR226(R) so that
difference between the recording/playback
level and the reference level is
-28 dBs 0.5 dB on both channels.
tape, the bias current
2
Increase in high
frequencies
Low bias current
Appropriate bias current
High bias current
Frequencies
1 kHz
12.5 kHz
Standard value Adjust point
Reference values
Metal tape:1150 uA
CrO tape: 700 uA
2
Normal tape:590 uA
LINE IN:
-19 dBs 2 dB
12.5 kH level: Deck B
0 0.5 dB L : VR146
higher than the R : VR246
1 kHz level.
Normal: Deck B
-28 dBs 0.5 dB L : VR126
CrO /Metal: R : VR226
2
-28 dBs 1 dB
(Difference between
L and R within
0.5 dB)