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RS-B25
m MEASUREMENTS AND ADJUSTMENTS
VR301, 302
VR7, 8
Bias Current Adj.
Overall Gain Adj.
Fig. 1
MAIN P.C.B.
VR85, 6 P.B.
Gain Adj.
NOTES:
Set switches and controls in the following positions, unless otherwise specified.
* Make sure heads are clean
¢ Input level controls: Maximum
¢ Make sure capstan and pressure roller are
¢ Dolby NR switch: OUT
clean
¢ Balance control: Center
¢ Judgeable room temperature 20+5°C (68+9°F)
@®
Head azimuth
Condition:
Equipment:
adjustment
¢ Playback mode
¢ EVM (Electronic Voltmeter)
¢ Normal tape mode
* Oscilloscope
¢ Test tape (azimuth)...QZZCFM
@® Tape speed
Condition:
Equipment:
e Playback mode
¢ Digital frequency counter
¢ Normal tape mode
* Test tape... QZZCWAT
L-CH/R-CH output balance adjustment
1. Make connections as shown in fig. 2.
. Playback the 8kHz signal from the test tape (QZZCFM).
Adjust screw (B) in fig. 3 for maximum output L-CH and R-CH levels.
When the output levels of L-CH and R-CH are not at maximum at the
same point adjust as follows.
. Turn screw (B) shown in fig. 3 to find angles A and C (points where
peak output levels for left and right channels are obtained).
Then,
locate angle B between
angles A and C, i.e., point where L-CH and
R-CH outputs are balanced. (Refer to figs. 3 and 4.)
L-CH/R-CH phase adjustment
4. Make connections as shown in fig. 5.
5. Playback the 8kHz signal from the test tape (QZZCFM).
Adjust screw (B) shown
in fig. 3 so that pointers of the two EVMs
swing to maximum and a lissajous waveform as illustrated in fig. 6 is
obtained on the oscilloscope.
Oscilioscope
LINE OUT
C
Record/ playback
head
KA
wa"
Screw (B)
Fig. 3
-
k
Een: peak:Jevel
R-ch peak level
OUTPUT
LEVEL
Vertical
Horizontal
Tape speed accuracy
1. Test equipment connection is shown in fig. 7.
2. Playback test tape (QZZCWAT 3,000Hz), and supply playback signal
to the digital frequency counter.
3. Measure this frequency.
4. On the basis of 3,000Hz, determine value by following formula:
f-3,000
Tape speed accuracy = 3000
*100(%)
where, f = measured value
5. Take measurement at middle section of tape.
Standard value: +0.33% (3000+ 10Hz)
6. if measured value is not within the standard value, adjust it by using the tape speed adjustment VR shown in
fig. 1.
Note: Please use non metal type screwdriver when you adjust tape speed accuracy on this unit.
Tape speed fluctuation
Make
measurements
in same
manner
as above
(beginning,
middle
and end of tape), and determine
the
difference between maximum
and minimum values and calculate as follows:
f,-f,
Tape speed fluctuation = 3.000 x100(%)
f, = maximum value, f, = minimum value
Standard value: Less than 1%
* Test tape...QZZCFM
=e
4. Make measurements
for both channels.
5Hz
6.3Hz'8kKHz 10kHz
Fig. 8
©
Playback gain
Condition:
Equipment:
e Playback mode
* EVM (Electronic Voltmeter)
¢ Normal tape mode
° Oscilloscope
* Test tape...QZZCFM
1. Test equipment connection is shown in fig. 2.
3. Make measurements for both channels.
[ Standard value: 0.4V+0.05V |
Adjustment
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