Panasonic RS-B25 - Measurements and Adjustments; Tape Speed Calibration; Head Alignment and Balance; Frequency Response Testing

RS-B25
m MEASUREMENTS AND ADJUSTMENTS
Tape
speed
adjustment
VR
Erase
Current
Adj.
Jumper
Wire
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%
@
Playback
frequency
Condition:
Equipment:
response
¢
Playback
mode
*
EVM
(Electronic
Voltmeter)
¢
Normal
tape
mode
¢
Oscilloscope
* Test tape...QZZCFM
=e .
Test
equipment
connection
is
shown
in
fig.
2.
—
frequency
response
chart
2.
Playback
the
frequency
response
portion
of
test
tape
(QZZCFM).
Spier
Ly
-
|
+508
3.
Measure
output
level
at
315Hz,
12.5kHz,
8kHz,
4kHz,
1kHz,
pe
250Hz,
125Hz
and
63Hz,
and
compare
each
output
level
Met
thy
with
the
standard
frequency
315Hz,
at
LINE
OUT.
Samet
UT
NE
PO
63Hz.100Hz-
meas
500Hz
1kH2
2kHz
4kHz
{
\
Sort
SkHz
4. Make measurements for both channels.
5Hz 6.3Hz'8kKHz 10kHz
5.
Make
sure
that
the
measured
values
are
within
the
range
specified
in
the
frequency
response
chart
(Shown
in
fig.
8).
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.
2.
Playback
standard
recording
level
portion
on
test
tape
(QZZCFM
315Hz)
and,
using
EVM,
measure
the
output
level
at
LINE
OUTs.
3. Make measurements for both channels.
[ Standard value: 0.4V+0.05V |
Adjustment
1.
If
the
measured
value
is
not
within
the
standard,
adjust
VR5
(L-CH)
or
VR6
(R-CH).
2.
After
adjustment,
check
“Playback
frequency
response”
again.