Mitsubishi DA-C20 User manual

TUNER.PREAMPLIFIER
DA- C20
SERVICE MAN UAL
ArYrrrsuBrsH!
AM /FM STEREO
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MELCO SALES, INC.

SPECIFI CATfONS
1-(1) FM TT]NER SECTION (IHF)
Us$Ie sensj-tivity
MONO
STEREO
50 dB quieting sensj,tj-vity
MONO
STEREO
Signal to noise ratio
Frequency response
Total harmonlc distortion
(at I kHz, 65 dBf)
MONO
Spurious response ratio
Image response ratio
IF response ratio
AM suppression ratio
MONO 80 atB
STEREO 75 dB
r1.2 dBf (2.0UV)
22.7 dBt (7.5tvl
19 .2 dBf (5. o'UV)
39 .2 dBf (5ouv)
11 dB from 30 Hz to 15 kHz
0. o5? (r.JrDE)
o.2* (NARROIi)
0.083 (wrDE)
0. 5r (NARROW)
o.8 dB (wlDE)
I.5 dB (NARROW)
75 dB (NARROW)
90 dB
80 dB
80 dB
55 dB (WIDE)
50 dB (NARROW)
STEREO
Capture ratio
Alternate channel selectivity 45 dB (WIDE)
v
Stereo separation
WIDE 45 dB at 1 kHz, 35dB at 10 kHz
-2-

NARROW 40 dB at 1 kHz, 30 dB at 10 kHz
Subcarrier product ratio 70 dB
SCA rejection ratio 70. dB
Tuning range 88 l,lHz to I08 I,$Iz
1- (2) rM TUNER SECTTON (DrN)
Sensitivity (at 40 kHz tleviation)
loNo (s/N 26 alB)
STEBEO (S^{ 46 dB)
I. 2uV
32pv
Image frequency rejection (at 98 MIIZ) 78 dB
I!' rejection (at 98 l{Hz) 85 dB
spurious rejection (at 98 MHz) 90 dB
AM suppr.ession 60 alB (WIDE)
55 dB (NARROW)
Selectivity 40 dB (WIDE)
(at 40 kHz deviation, 13oo kHz) 70 dB (NARROW)
Signal to noise ratio
(at 40 kHz tleviation)
!,roNo 75 dB
STEREO '?2 dB
Total harmonic distortion
(at 1 kHz, 40 kHz aleviation)
L4ONO 0.06r (WIDE)
0.15t (NARROI{)
STEFEO O.O8A (MDE)
0. 3s (NARROW)
Stereo sepaxation 45 dB (WIDE)
(at 1 tiHz, 40 kHz alevi ation) 35 dB (NARROW)
11 dg from 30 Hz to 15 kEz
- 3-
Frequency response
l

2-(1) AM TUNER SECTION (IHF)
Usab1e sensitivity (bar antenna) 45 dB
Selectivity 30 dB l -_/
Total harmonic distortion O. 8E
Image response Latio 40 dB
IF response ratj-o 70 dB
Hr]m and noise 50 dB
Tuning range 525 kttz to 1605 kHz
2. (2) p.J'q TUNER SECTION (DIN)
Selectivity (bar antenna, at 3Og 3OOUv/m
modulation, S/N 26 dB)
Signa1 to noise ratio 50 dB
(at 5 mVlm, 308 modulation)
Selectivity (at t9 kHz) 30 dB
Image frequency rejection (at I IGtz ) 40 dB
IF rejection (at t MHz) 70 dB r,.
Tota1 hamonic distortion O-8*
(at 308 modulation)
3 PREAMPLIFIER SECTION
Input sensj" ti vi ty/impedance
PHoNo MC 0,1 mvlto ohms
PHONo MM 2.3 mv/sC.k ohms/l0O pF
AUX, PLAY 1, PLAY 2 L5O mVl5Ok ohms
output level/impedance
oUTPUT 1v (rated output) /600 ohns
18V (maximum output)
REc 1, REC 2 15O mVl6OO ohms
PHoNES (8 ohms ) 600 mv (at output lv) /15 ohms
650 mV (maximum output) (headphone
impedance from 8 ohms to 16 otms )
- 4-
l_,

Equivalent input noise leve1
(IHF, A network)
PIIONO MC -I57 dB(v) (47 ohns- terminated)
PHONO MM -136 dB(V) (closed circuit)
AIIX, PLAY I, PLAY 2 -126 dB(V) (closed circuit)
Signal to noise ratio
(IHF, A network at rated output)
PHONO MC
PHONO MM
AUX, PLAY I, PLAY 2
Signal to noise ratio (DIN)
PHONO MC
PHONO MM
AUX, PLAY 1, PLAY 2
Total harmonic distortion
(at rate d output attenuator -20 dB
v from 20 gz to 20 kP.z)
PHONO MC
PHONO MM
AUX, PLAY 1, PIAY 2
ChaInel separation
PHONO MC, PHONO MM
PLAY 1, PLAY 2
Tone control
BASS
TREBT,E
77 dB (47 ohms terminated)
84 dB (closed circuit)
110 dB (closed ci rcuit)
72 dB (47 ohms terminated)
73 dB (2.2k ohms te rminated)
106 dB (closed circuit)
92 dB (47k ohms/250 pF terminated)
PHONO MC, PHONO MM crosstalk is less than noise level at
1 kHz, 80 dB at 20 kHz
PLAY l, PLAY 2 Crosstalk is less than noise level at
I kHz, IO0 dB at 20 kHz
Frequensy response
0,0058
0.003?
0.003?
10.2 dB from 20 Hz to 20 kHz (RIAA STD)
+O
_6.S @ from 10 Hz to I00 kHz
lI0 dB at 100 Hz
1I0 dB at I0 kHz
-5-

Subsonic fi Ite r
Phono overload 1eve1
(at t kHz with 0.18 THD)
PHONO MC
PHONO MM
Power consumption
Dimensions (wxHXD)
Weight
Supplied withr T shaped antenna
18 Hz (-6 dB/oct\
12 mv
290 mv
30w
425 x l1o x 292 mm
(L6-3/4 x 6-3/4 x tL/t/2"',t
7.5 ks (L6'L/2 I'bs\
Desiqm and specifications are subject to change without notice for improvements.
SERVICING NOTES
1. Before connection, turn off
the power supply at all times
othemise, the speakers are IiabIe
to be damaged by click -noise caused
when the cord if plugged in or out.
2. Avoid improper connection
when tur.ntable, tuner, and R
and L of output terminals of this
machine are incorrectly connected
or short-circuited, stable sound. 5-
production cannot be achieved.
3. Correctly make input terminal
connect ion
When pin plug or earth wire of
record player output cord is loosely
connected or disconnected, hum
occurs. Note that the speaker is
Ii-able to be damaged \,rrhen such in-
correct connection is not remedied.
Use shielded wire for input
terminal- connection
Use a shielded wire of not more
than 2 m Iong for connections to
record player and trner. In this
case, avoid the use of longer
shielded wire which causes deter-
ioration of high band character-
istics and easy catching of hum
and noise,
Use the machine \,rith a pin
plug for short- c.ircuiting
use in PHONO termlnal unused
This is intended to prevent open
noise, and click noise caused when
the input selector is switched
without connecting a turntable.
I,lhen you use Mitsubishi DA-AIODC or
DA-A15DC in combination with this
machine, power of the power ampli-
fier must be supplied from SWITCHED
plug sockets of this machine.
The speaJcer control cord is
used for only Mitsubishi power
amplifiers.
4.
-6-

DESCRIPTION AND FUNCTION OF EACH PART
I FRONT PANEL
1F BAND (selectivitl, switch)
This selectivity switch is for choosing the IF
band-width and may be switched between the wlDE
(with 45 dB selectivity) and the NARRoW (with
75 dB selectivity) for reception,
WIDE For receiving an FM broadcast when
there is no interference from nearby
stations. In Urj-s position, the lowest
distortion reception is obtained.
NARROW For receiving an FM broadcast in a
crohrded broadcast area to eliminate
interference from nearby stations.
E
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S PEAKE RS,/OUTPUT
(Speal<er Selection switches)
When using the companion power ampli-
fier (DA-AloDc. DA-A15DC) , the speak-
ers connected to the power amplifier
may be controlled with these switches.
The "speaker control cable" supplied
with the power amplifier must be
connected, to utilize these switches,
AB
I I For listening v,/i th headphones.
Preamplifier outputs are off
and no sound will be produced
from the speahers.
r. I For listening to the speakers
connected to the A terminals
on the power anpli fier,
I r For listening to the speakers
connected to the B terminals
on the power ampli fier,
r .r. Ior listening to the speakers
connected to both A and B
terminals on the power ampli-
fier.
SELECTOR (rnput selection switch)
This switch selects the desired pro-
gram source.
PHoNo MC This position is used for
playing a disc on the turn-
table equipped wj- th a MC
(moving coil) cartridge and
connected to the PHONO MC
inputs.
PNOHO I4I{ This position is used for
playing a disc on the turn-
table equipped with a MM
(moving magnet) cartridge
and connected to the PHoNo
MM inputs.
TUNER For listening to programs
on the AM/FM tuner.
AUx For playing a second tuner,
turntable with a high out-
put ce ramic cartridqe, taPe
deck for playback use, tele-
vision audio, or any suit-
able hiqh output sources
connected to the AUli inputs.
-7-

I DISASSEMBLING TUNER SECTION
AND PREAMPLIFIER SECTION
]- Removal of the Top Plate and
the Bottom Cover
1) After removing the trro screws
indicated as A in Fig. 1, take
off the top plate, pulling it
toward the back.
2) The cabinet is removed by taking
off the four screws indicated as
B in Fig. 1 as well as the two
screws located at the bottom.
2. Removal of Front Panel
1) Take off the two upper panel
fixing screws indicated as D in
Fig. 4.
2) Take off the two lower side
panel fixing screws indicated
as C in Fiq. 2.
3) nemove.the controls on the
front parrel. (Being of a hexa-
gonal screw type, the tuning
knob (T in Fig. 3) should be're-
moved by me ans of a hexagonal
screw driver having a 2 run op-
posite side.) As regards the
rest of the knobs and controls
except the push control. the four
control (v) and I knobs (I,l)
should be renpved by pulling them
out in a forceful manner toward
this side.
4) In this condition, the front
panel can be taken off toward
this side.
3. Removal of Tuner Section
L) Disassemble the alunrinum inlay of
the tuner sectj"on by removing the
four screws indicated as E i,n
Fig. 5.
2) Take off the three chassis-fixing
screws (F in Fig. 2) of the
tuner section.
3) Remove the two front-chassis-
fixing screws (G of Fig. 5) of
the tuner section.
4) Remove the rear-chassis- fixing
screws (H of Fig. 1) of the tuner
section.
5) Take off the side panel and holder
assenbly screw (J in Fig. 4).
Fig. I
FLq,2
Fi g, 3
*"[.1;oanE.S @"P
. ,9
9\ B ",@'ol
'B B'
"6"'6 o -'s'
i '*' tLr
^ ow5i, *" .ro ill:
-,.o.ooc
- 8-
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6) with the right side panel spread
outward from its normal pos.ition,
lift up the turer section and
arranqe it as shown in Fig. 6.
To prevent sho rt- ci rcui ting be-
tween the tuner section's chassis
and the preamplifier's printed
ci rcu.it board, insert a cloth or
the like in between,
7) with the set in this aondition,
the front end can be adjusted.
8) To remove the printed circuit
board from the chassis when re-
placing the parts on it, the
follo\^7ing screws are to be re-
mo ved.
(1) Take off the two holder set-
screws for meter mounting
(K in Fig. 7) .
(2) unscrew the two push switch
assenbly screws (L in Fig, 7) .
(3) Unscrew the two printed cir-
cuit board assenbly screws
(M in Fig. 7).
Disassembl-ing Preampli fie r
Section
1) The order of disassembly is the
same as that for the tuner
section, steps l) through 6).
However, at Step 6), the tuner
section should be placed at the
back.
2) Remove the two front chassis
fixj-ng screws (N in Fig. 5) of
the preamplifier se c ti on.
3) Remove the three volume fixing
nuts (P of Fig. 5) of Lhe front
chassis section,
4) Take off the switch assenbly
screw (Q of Fig. 5) of the front
chassis section.
5) Remove the two printed circuit
board (PA-66) asse(0f,ly s crews
(Y in Fig. 4).
6) Remove the coupling section (in
the direction of R shown in
Fig. 6) of the selector switch
and extension shaft.
7) Lift up the front chassis and
turn the printed circuit board.
PA-67 toward this side. (The
condition sho\am in Fiq'. 6)
Fig.6
Fig.5
P.C Board
P.C Board
M
l\4
-9-
Fiq.7

Remove the shield plate by un-
screwing the shield Plate
assembly screw (S in Fig. 5)
located between Pr.inted circuit
boards PA-66 and PA-67.
With the set in this conditioo,
it is possible to replace the
parts provided on printed cir-
cuit boards PA-65 and PA-67.
ADJUSTMENT
1. Printed Circuit Board
(PA-6 6 )
L) set the semi-fixed resistor
vRsol comPletelY in the conter-
clod(wi-se di rection '
2) set the power s\ri tch to oN
position.
3) Connect the voltmeter to the
ground terminal (34) and the
terminal (33) on +B side and
turn the vF50I clockwise (in
the arrow direction) to ad.just
it so that it may indicate
33!0. 5 (v) .
4) Connect the voltmeter to
the ground terminal (34) and
the ten[inal (35) on -B side
and confirm that it indicates
-3311.s(v).
2. Printed Circuit Board
(PA-57)
1) Set the semi-fixed resistor
VR5O1 completely in the cormter-
clockwise direction.
2) Set the power switch to oN
posltion.
3) Connect the voltmeter to the
ground terminal (84) and the
tenrrinal (83) on +B side and
turn the vR60l clockwise (in
the arrow direction) to adjust
it so that it maY ind.icate
3310.5(v).
4) Connect the voltmeter to
the gror:nd terminal (84) and
the terrdnal (85) on -B side
and confirm that it indicates
-3311.5(v).
View seen at copper foil side
The side whe re the parts of the
printed circuit board (PA-67)
are inserted.
8)
9)
To adjust this printed
circuit board, the
tuner section must be
removed. pA-66
- lo-

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 -

5) Turn off the Pilot signal and
modulation signal of the stereo
modulator. with a frequency
counter connected to Pin (120),
adjust the vR so that the frequ-
enqf may be within the range of
76!0.2 kEz.
Turn the pilot signal oN and
confirm that the stereo indicator
lights up.
with the modulation of the stereo
modulator set to either "R" or
"L", adjust vR632 so as to make
separation maxj-mum.
THREADTNG ON DIAI
I ADJUSTMENT OF AM SECT]ON
I. Tracking Adjustment
1) with the SG's sigmal set to
600 kHz and 400 I1z to 30% modu-
lation, and the indicator of the
set tuned to 60O kHz, adjust the
corlrANT (L27I) and Corr-osc
(T271) so that the outPut will
may become maximum.
2) with the SG's sig.nal set to
I,4OO kHz and the indicator of
the set t1med to I . 400 kHz,
adjust the antenna trirurcr TC27l
and local oscillation trimmer
TC272 in a way to make the outPut
rnaximum.
3) Repeat f) and 2) several times'
\i"
6)
7)
e-/
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-L2-

PRINTED CIRCUIT BOARD
PA-67
i
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I
PA-66
- 13 -

-vI -
1-
lr
lf,
E
99-Vd

PA-65
v
PA-65
-15
r-,

PA.65
PA-65 PA.65
-16-

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