Revox B261 Serviceanleitung Seite 45

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8261 SA
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414
4.4 Adjustinq the IF ampl-j-fier I.726.730/740/750
Required
test
equipment
:
-
Fl4
standard-signal
generator
-
RF
voltmeter
- Digital
frequency counter
with
CRO
probe
10:1
Adjusting
procedure:
-
Connect
RF
voltmeter to test point
MP3
(R17, IC3 Pin l,
I.726.740, Fig. 4.4).
-
Connect
digital frequency counter
to test point
MP4
(L.726.740,
E':-g.
4.4)
.
- Press
station selector key 3 (98.0
MHz).
- Feed 200
... 400 pV EMF, 98.0
MHZ
from the standard-signal
generator into the
antenna
input.
The
IF
must
not
be
clipped.'
- Adjust the transmission
frequency so
that a reading of
10.7
MHz
+1 kHz is obtained
on
the
frequency counter.
- Adjusr
LI6/LL2/LL3 through
LlB (1.726.730, Fig. 4.3)
and LI/L2
(I.726.740), Fig. 4.4) for
maximum
reading on the
RF
voltmeter.
Since
there is mutual influence between
the coils,
these adjustrnents should be repeated several times.
- Adjust level of the standard-signal generator to obtain
a
reading of approx.
500
mV
on
the
RF
voltmeter (IC2
shouLd
not
clip).
- Vary
receiving frequency (98.0
MHz)
by
+50 kHz and
by +
100
kHz
(with staiion seleclor keys
15,/13
aia tZ,zff
- The
level
on
the
RF
voltmeter
should
only vary by the following
magnitude:
Frequency
change
+ 50
kHz
T too
t<Hz
- If these values are not attained, the settings of the
trimmer
slugs
L10 and L12 through
Ll7 (L.726.730, Fig. 4.3)
should
be
changed
until the specified tolerances are met. If
a
correction is necessary, it should
be
made
with all
trimmer
s
lugs
.
The
IF leve1 should not
change
as a result.
The adjustment
of the IF filters
should be balanced as
closely
as possible.
- Press
station selector key
14
- Disconnect frequency counter from
MP4.
-
connect
RF
voltneter to test point
MP6
(R21, Ic4, pin l,
L.'126.740, F:-g.
4.4)
and
adjust L3 for
maximum
voltage.
-
Connect RF
voltmeter to test point
MP4
and
adjust L4 for
maximum
voltage (Fig. 4.4).
-
Connect
RF
vol"tmeter
to test point
MP7
(R29, fC3 pin
1,
I-726.750, Fig. 4.5)
and
adjust L7 for
maximum
voltage
(
approx.
400
mV) .
4.5 Adjusting the
demodulator
1.726.750
Required
test
equipment:
-
Generator up
to
200 kKz
-
AF
voltmeter up to
200
kHz
- Digital voltmeter
- Frequency counter
Adjusting
procedure:
- Connect AF
voltmeter to test point
MP9
(Jl pin 2, I.726.750,
Frg.
4.5
)
- Switch tuner off
and
carefully pull
IC4
out of its
base.
Connect
generator
and frequency
counter to test point
MP8
(R20, Fig. 4.5).
-
Swi.tch
tuner on
and
adjust filter for
maximum
voltage
(generator voltage
=lV)
:
Generator
frequency Filter
176.8
kHz
L6
101.
5 kHz
L5
99.2 k]
z
L4
114
.0 kHz
L3
Figo
4o5
Response
down
-I.8
.
.. 2.2
dB
-8.5 ... 9.5
dB
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