Mitsubishi DA-C20 Service Manual page 11

I
FM
SECTION
l. Front
End Adjustment
1) With the signals of the signal
grenerator
(SG) connected
to
the
FM-ANT
terminal, take out
the
setrs output
from
test point
r.
P. (119).
2) With the
SGrs
frequency set to
87
1fr12,
turn the dial fully
coun te rc
lockwis
e
so
that
the
turer
may
indicate the
lowest
frequency. Adjust the local
oscillati-on coil so as to
make
the signals
generated by the
SG
maximum.
3) With the
SG's frequency
set to
109 MHz,
turn the dial
fu11y
clockwise so that the
tuner
indicator
may show
the
maxi-
mum
frequency. Adjust the
1ocaI
oscillation
trinuner Ct91 in
a
manner
to
ma]<e
the
SGrs
signal
maximrm.
4)
Repeat Steps
2)
and
3)
several
times
.
5) With the
SGrs
frequency set
to
88
MHz,
set the tuner to indicate
88
MHz
with the dial.
Adjust
coils
L171, LL72
and.
LI73 so
as
to
make
the output
naxi
mum.
6) with the
SG's frequency set to
108 MHz,
set the tuner to indi-
cate to
108 ItrIz
with the dial.
Adjust triruners
TC171, TCI72
and
TC173
so as to
make
the
output
maximum.
.
Adjustment
of
FM-MONO
1) Set the
SG
to
9
8
t"!rtz,
4OO
Hz
Lo
MONO
l00A modulation and
the out-
put to
B0
dB.
2) Set the selector
s\,ritch of
the
set to the
FM
position
and the
mode
to
FM-MONO/MUTING
OFF and
SELECTI VI TY.WI
DE .
3) Adjust the
secondary side
core
(upper
side) of
T8O2
so
that
the
center meter
may
indlcate
the
center during detuning
(
approxi-
mately
l-00
MHz).
4)
Tr:ne
the set to the
SG's
fre-
quenc)l (98
MHz). Tuning,
in
this case. is attained
when
the
center meter is a state in
whicf-
it indicates the
cen
te.r.
Next, with the
mode
switch
set
to
FM-AUTO/MIj'I1NG-ON,
adjust
VR751
so as to
make
the
center
fieter indicate the
center.
5) After
connecting a distortion
meter to the output pin
Lerminal
, adjust the
primary
side core
(1ower
side) of
T8O2
so as ta
make
the distortion
factor
minimum. In this
case,
if the center
meter
does
not in-
dicate the center, adjust
the
secondary
side of
T802 again
until it
does.
6) Adjust
T803
so as to
mal<e
the
swing of the
s19na1 meter
maxi-
mum.
7) Adjust
VR801
so that the siqnal
meter
may become
4.7
o]j)
the
scaIe.
3. Adjustment of
FM-MPX
1) Set the
SG
to
98
MHz,
L
k:H.z
STEREO
to
L+R
902.
pilot to
10%
modulation arld the output to
80
dB.
2) Set the selector switch of
the
set to the
FM
position
and
mode
to
FM-MONO/MUTING-OFF
and
to
SELECT]\rITY-WIDE
.
WhiIe receiving
98
tr&tz
signals
from the
SG,
adjust the local
oscillation
trimmer
C191
of
the
front
end
in
a
manner
to
make
the indicator indicate
9g
MEz
on the dlal pIate.
3)
Place the set to
FM-AUTO/MIITING-
ON. Shift the position of
the
indicator to the feft
and
right
from 98
MHz
and confirm that
LOCK
aid
MUTING
operations
are
normal
.
4) After turning the set again
to
98
ltfr1z,
drop the
SG
output
and
adjust
VRB02
so that the
wave-
forms
may
disappear (which
im-
plies that the output is
zero)
at
26
dB and re-appear at
27
dB.
- 11
-