Pioneer SX-303 User manual

YQ) PIONEER
CIRCUIT
DESCRIPTIONS
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REPAIR
&
ADJUSTMENTS
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AM/FM STEREO RECEIVER _
MODEL SX-303 (SX-303L) COMES IN FIVE VERSIONS DISTINGUISHED AS FOLLOWS:
Model | Voltage : Remarks |
SX-303/KU | = AC120V only - oats Fe | ou S.A. model
SX-303/KC AC120V only | | ¥ = a Ee | . fF Canada model
SX-303/S Pe ACT 10V,120V, 220V and 240V (switchable) General export model |
: a SSiSSaRcnL: ETT aidan acienaaemeatae r i nt treet ee a yee ee et Or
SX-303L/HE | AGC2Z2Z0V Oaly 4 he ow BS European continent model with AM-LW band tuner |
| SxX-303L/HEZ | AC220V Only OE os pee toe! aS ay | - =: West germany model with AM-LW band tuner |
@ This service manual is applicable to the Ku types. For servicing of the thier types, please refer to the
additional service manual. cae eae
® Ce manuel d’instruction se ice au faode. ite réglage, en frangais:
@ Este manual ae | servicio trata del metodo de ajuste escrito en n espaol.
CONTENTS
_ SPECIFICATIONS .............0000002. 2 8. P.C. BOARDS CONNECTION DIAGRAM rae
1
2. FRONT PANEL FACILITIES. .0..00..0.000.. 3 9. SCHEMATIC DIAGRAM ... ae eee ee
3. PARTSLOCATION ....... Sf ade ned: 4 10, ELECTRICAL PARTS LIST.......... ae
4 BLOCK DIAGRAM so ocds acide, 5 11, DIAL CORD STRINGING .. ne Ae
5. CIRCUIT DESCRIPTIONS . he eae ie 6 12. ADJUSTMENTS ae eee ata gia cane 20
6.
PACKING........0.-.
0.
-
Lees.
—
REGLAGE
........0...,
—-
aie
tee
7 EXPLODED VIEW AND PARTS List eee SO _AJUSTE ae cewtewua sete tuk, sates. Oe
RBPIONEER ELECTRONIC CORPORATION 4-1. Meguro 1-Chome, Meguro-ku, Tokyo 153, Japan
PIONEER ELECTRONICS (USA) INC. 1S25 £. Dominguez St., Long Beach, California 90810 UW. S.A.
PIONEER ELECTRONIC [EUROPE] N.V. Keetbergiaan 1, 2740 Severen, Belgium
PIONEER ELECTRONICS AUSTRALIA PTY. LTD. 173-184 Boundary Road, Braeside, Victoria 3195, GSE
YX © DEC. 1982 Primte d in | ea Ut

1. SPECIFICATIONS
Amplifier Section
Continuous Average Power Output is 45
watts* per channel, min., at 8ohms from
40Hertz to 20,000 Hertz with no more
than 0.3% total harmonic distortion.
Total Harmonic Distortion (40 Hertz to 20,000 Hertz,
8 ohms, from TAPE)
continuous rated power output
ot ta ite; Morahan rir ule Ae ee ee ance No more than 0.3%
22.5 watts per channel power output
Sie Ge Rcaree bani wee BL Le No more than 0.15%
| watt per channel power output
ee eee ee ee eee are eae No more than 0.2%
intermodulation Distortion (50 Hertz: 7,000 Hertz =4: 1,
8 ohms, from AUX)
continuous rated power output
ao oh fie ais Wns fs Beane ek ee No more than 0.3%
Damping Factor (1 kHz, 8o0hms)...... 6a Sena ne tie 22
Input (Sensitivity/Impedance)
PHONO ................ 2.5 mV/50 kilohms
TAPE PLAY 66.0% 3044454 4% 150 mV/50 kilohms
Phono Overload Level (T.H.D.0.1%, 1,000Hz)
PHONG) se sak ea eo eee eae ewes 150 mV
Output Level
"PAPE REG cise erie ei bcec dale tim eae ele, 4 150 mV
SPEAKER............... A, B, A series B, off
Frequency Response
PHONO (RIAA Equalization)
bs kasi WOM exes: Mee eee 30Hz to 20,000Hz+0.5dB
TAPE PLAY.......... 15Hz to 50,000Hz *3dB
Tone Control
BASS, cei ery dee seat +9dB (100Hz)
PPG BEE ery, eis hows aarp aie +9dB (10kHz)
Loudness Contour (Volum control set at- 40dB position)
Rr a ee eee +8dB (100Hz), +6dB (10,000H2z)
Hum and Noise (IHF, short circuited, A network)
PHONO MM..............00c ee eee 71dB
"ARP PLAY ot se cw ee me “es eR ede 97dB
FM Tuner Section**
Usable Sensitivity ............0. 10.7dBf (0.9nV)
50dB Quieting Sensitivity
MONO: 4 occcda ee ace Be Bans &4 15.3dBf (1.6uV)
STEREO <4 4054 eed was 37 .6dBf (21uV)
Signal-to-Noise Ratio
MON Os. oie ees 6-228 ee a ed 75dB (at 85dBf)
STEREO «6-35. hie k Chase 4 SS3 70dB (at 85dBf)
Distortion (at 65dBf)
MONO TKAZ cee sc bt ee es 0.3%
STEREO kHz ...........0 000 eens 0.6%
Capture Rate 24 Bee cS GEESE EO NS , 2.5dB
Alternate Channel Selectivity (400kHz) ....... 50dB
Stereo Separation (1kHz)................. 35dB
Frequency Response ....... 30Hz to 15kHz, 76 dB
Spurious Response Ratio .............,... 70dB
Image Response Ratio ............... 0005 45dB
IF Response Ratio .................204. 100dB
AM Suppression Ratio .............-...0. 45dB
Subcarrier Product Ratio........ 2.0002 ee eae 31dB
Muting Threshold .............-. 27d Bf (6.3uV)
AM Tuner Section
Sensitivity
IHF, Loop antenna................ 3202 /m
IHF, Ext.antenna........... Beaty ab-werds tele 30uV
Selectivity ....... hae aceste a ah e Aine es 25dB
Signal-to-Noise Ratio... 2... 0.0... ee ee 43dB
Image Response Ratio .............00008- 40dB
IF Response Ratio ............. 0000 bees 45dB
Antenna ............000008 AM Loop Antenna
Miscellaneous
Power Requirements ............ AC 120 V, 5OHz
Power
Consumption
...
190
Watts(UL),
225
VA(CSA)
Dimensions ........ 420 (W) x 98 (H) x 214(D) mm
16-9/16(W) X 3-7/8(H) X 8-7/16(D) in
Weight (without package)............. 5 kg (11 Ib)
Furnished Parts
FM T-type Antenna ...........0000 2 eee, |
AM Loop Antenna ............ 0.0.00 cee . 1
Operating Instructions ............0 2.008 ee el
*Measured pursuant to the Federal Trade Commission’s Trade
Regulation rule on Power Output Claims for Amplifier.
**FM muting functions with this unit when the signals are veak.
The unit’s internal wires are therefore treated so that the sirrals
are not muted when the sensitivity is measured.
NOTE:
Specifications and design subject to possible modification wih out.
notice.

2.FRONT PANEL FACILITIES
)
a AM sa ec
@) POWER SWITCH
Push this to switch on and off the unit’s power. Power is
supplied at the depressed (=) switch position (ON) and
turned off at the released (IL) position (OFF).
(2) HEADPHONE JACK
Connect the plug on the stereo headphones to this jack
when listening to sound through headphones.
(3) TONE CONTROLS
BASS : The bass is increased when this control is rotated
clockwise from the center position and reduced
when rotated counterclockwise.
TREBLE :The treble is increased when this control Is
rotated clockwise from the center position and
reduced when rotated counterclockwise.
(4) BALANCE CONTROL
This is normally kept at its center position. It is rotated
when the volume of sound delivered through the left and
right channels of the speakers or headphones differs.
The right channel volume is reduced when the control is
rotated toward the LEFT from the center position while
the left channel volume is reduced when it is rotated
toward the RIGHT.
(S) FUNCTION SWITCHES
PHONO : Press when listening to records.
FM : Press when listening to FM broadcasts.
AM : Press when listening to AM broadcasts.
(6) TAPE (ADPT) SWITCH
This is depressed when using a tape deck or adaptor unit
connected to the rear panel TAPE/ADAPTOR jacks.
@ LOUDNESS SWITCH
Depress this switch to the ON position when Sistening to
sound at a low level of volume. This will enhance the bass
and treble and give more life to the sound even at a low
volume.
EO ASCEVER $x-3903
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100 caf
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VOLUME CONTROL
Use this to adjust the volume of the sound delivered
through the speakers or headphones.
The volume is increased when this control is rotated
clockwise from the minimum “0” position.
@Q) TUNING INDICATOR (TUNING)
This lights up to indicate that an FM, AM station has been
tuned in.
STEREO INDICATOR (STEREO)
This lights up automatically when an FM station broad-
casting in stereo has been tuned in.
d) SPEAKERS SWITCHES
These are used to select the speakers through which you
will listen to the sound.
The selected speakers are now working.
A: The sound is heard from the speakers connected to
the speaker A terminals on the rear panel.
B: The sound is heard from the speakers connected to
the speaker B terminals on the rear panel.
No sound will be heard when SPEAKERS A and B switches
are both released. This is the position at which the sound
can be heard through the headphones.
NOTE:
No sound will be heard through the speakers when both the A
and B switches are depressed if only one set of speakers has been
connected to either the A or B SPEAKERS terminals.
(2 FREQUENCY SCALE
This indicates the frequency of the broadcasting station
(FM, AM).
The top level figures (88 ~ 108) indicate the FM band.
The bottom level figures (55 ~ 160) indicate the AM band.
(3) TUNING KNOB
Rotate this knob to pick up stations (FM, AM).
POWER INDICATOR

3. PARTS LOCATION
NOTES:
e Parts without part number cannot be supplied.
e The A, mark found on some component parts indicates the importance of the
safety factor of the part. Therefore, when replacing, be sure to use parts of identical
designation.
e For your Parts Stock Control, the fast moving items are indicated with the marks
kx and x,
**x GENERALLY MOVES FASTER THAN kx.
This classification shall be adjusted by each distributor because it depends on model
number, temperature, humidity, etc.
Front Panel View
Speaker knob —--———-—__--—____-- Bonnet
AAD-608 ANE 410
Front pane! assembly
ANM-293 = ; SOF ee om . ee i. r oes _ ce ores | owe é | eCo--— Tuning knob
6g EE ; | on AAA084
Power knob-————~—--__-_—_—___-.-__# : cae y ry os : € 2 Fe sa 7 : ‘
AAD-605
ace
tf
to
nae
ioc
[Moe
:
cra
pee
Phone jack —-—————---—___—___ Function knob A
AKN-045 (TAPE, LOUDNESS)
AAD-606
Knob B a - ——-___ | ————_—_———. Function knob B
(BASS, TREBLE, BALANCE) (PHONO, FM, AM)
AAB-317 AAD-607
Rear Panel View
~——— —_______-__-——- /\ aCsocket
Lv AKP-039
Earth terminal
Rear panel
Complex
terminal
—-_-————
(eee
A
AC
power
cord
AKX-073 ADG-073
Top View
Complex asermrbly
GWM-265
/\i%* Fuse (T2.5A) -
AEK-123
[\* Power transformer (120V) FM Front-end
ATT-944 AWB-O14
kk fC
NSt 53L
/\ we Push switch
(POWER)
ASG-541
*k* Functionsw itch
ASG-412
Switch assembly 7777

4.BLOCK DIAGRAM
FM FRONT END (173) FM.IF AMP
—
| soon
BAL
FM
| 750
UNBAL
[ GND
AM
LOOP
ANT
LED DRIVER
Re AaRaeey
FM FRONT END L mm |
(2/3) FM FRONT END
(373)
AM FRONT END
FM (Uch)
FM(Rch) | |
S1-|
Si-2
|
SI-3
S1-4
Si-5
POWER
ON/OFF
MUTING
PLAY
—
ie
a
Heer:
SOE
e)
ae
TONE
CONTROL
“igy.
“Se
Pes.
VR2-2,
2-3
EQUALIZER
AMP
0
°
eee
+82
(1/4)
i
ie
Se
;
g
USOmv|
Qi7|
poi7
06
+B2 AM +BI
18.9V| PHONES
+B2
FM
2
6
|
!
|
|
|
!
{
!
O : VR I
0)
+B2
:
O
:
O
2
ii
(3/4,4/4) (2/2)} (2/4)
POWER AMP
=
$1-4 $1-5
peene
(2/2)
(2/2)
Rch REC
PLAY
ia
ae
TO
POWER
SUPPLY
&
PROTECTOR
Reh
SPEAKERS
+B1(35V)
SP B
S101
°
POINTER
AC
120V
cS
ne
oe
e;
a8
08
1)
N
SP
A
“oy
z
;
SI-|
;
FUNCTION
(PHONO)
ON-OFF
|
9
bLanenmne
S1-2 : FUNCTION (FM)
Si-3.: FUNCTION (AM) |
$1-4 : TAPE MONITOR ON - OFF S2-1: SPEAKERS A (ON — OFF SIO : POWER ON — OFF
S!-5 : LOUDNESS ON - OFF S2-2: SPEAKERS 8 ON — OFF

5. CIRCUIT DESCRIPTIONS
FM Front End
A unitized variable capacitor type front end
unit 1s used consisting of an FET RF single stage
amp, local oscillator/mixer IC and an IF trans-
former.
FM IF Amp, Detector and MPX Circuit
A 2-transistor IF amp with ceramic filter is used
and the next stage has an IC (M51533L) contain-
ing the FM IF detector and MPX circuit. The block
diagram of IC M51588L is shown in Fig. 5-1. This
IC uses a peak detection method which can be
adjusted with a single coil. The PLL method is
employed to reconstitute the 38kHz sub-carrier
for the MPX circuit.
The IF signal is input at pin 1 and the detection
output is obtained from pin 5. The detection out-
put passes through the muting Q4, goes to pin 9,
passes through the MPX circuit and the stereo
signals are obtained from pins 11 and 12. In
addition, this unit detects the presence or absence
TUNING y)
| Z T.P 6
TP |
at ©
ms 3rd
1F
AM oO FM
S1-3 f ai L OUT
Fig. 5-1
paar, f
(6)
PHASE
\/2
\/2
ile Shan COMPARATOR| | “°° DIVIDER DIVIDER
1
! nes
L
LEVEL INPUT
@) alae BUFFER
CIRCUIT
STEREO (13)
: SWITCH Fiancee J IND 7
MPX
On
of a pilot signal to automatically switch between
stereo and mono reception by R14 which is con-
nected to pin 14. When a stereo signal is received, —
pin 13 drops to the low level to light the stereo
indicator.
When
pin
2
is
grounded,
the
PLL
VCO
and
FM
IF
operation
stop
(for
AM).
FM Muting and LED Driver
With
this
unit,
muting
is
automatically
activated
when
the
antenna
input
drops
below
10uV.
As
the
antenna
input
decreases,
the
voltage
at
pin
3
drops,
Q5
is
turned
off
and
Q6
is
turned
on.
As
a
result,
the
gate
voltage
of
Q4
drops,
Q4
is
turned
off
and
the
detector
output
circuit
is
blocked
(Fig.
5-1).
When
an
FM
or
AM
station
is
tuned
in,
the
base
potential
of
Q5
is
raised,
Q5
is
turned
on
and
the
tuning
indicator
lights.
A RI4
LL]
M5i533L
(10)
:
+B2
1/2
STEREO PHASE
FM 1F, Detector and MPX circuit

AM Tuner
This’ uses a variable capacitor type tuning
circuit composed of three transistors, a 2-tran-
sistor front end and a single transistor AM IF
detector.
AF Section
The equalizer circuit has a low-noise operation
amp (2 channel) M5218P.
The power amp has a 45; watt output power IC
STK4141-2S (See Fig. 5-4). |
The tone control circuit is placed in the negative
feedback loop of the power amp.
Protective Circuits
This unit has a circuit to detect DC voltages at
the power amp outputs and a muting circuit that
operates when power is turned on and off.
Fig. 5-2 shows the construction of the DC
voltage protection circuit. When a DC voltage
VOLUME
BALANCE
VOLUME
TO POWER AMP
appears at the power amp output, either Q13
(plus) or Q14 (minus) is activated depending on
the polarity of the DC voltage and a trigger is
applied to D15. This turns on D15, +B1 is shorted,
the fuse on the primary side is cut and the power
supply circuit is shut off.
Fig. 5-3 shows the power on/off muting circuit.
Time constant t, is longer than t, so that imme-
diately after the power is turned on, the emitter
potential of Q15 exceeds its base potential, Q15 is
turned on to activate Q16 and Q17 and ground the
signal. A few seconds later, the base potential of
@15 rises to turn off Q15 along with Q16 and Q17.
When the power is turned off, the charge of
C161 passes through D18; it is almost completely
discharged in an instant to make the base potential
of Q15 zero. However, because the charge of C160
remains, Q15 is turned on and muting is activated
in the same manner as when power is turned on.
TO
SPEAKER
SWITCHES
+B3
tr,t2 * time constant
Fig. 5-3. Power ON/OFF muting circuit

f--------
=
12 11 Vee
t
|
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|
|
IN 1(+)0
|
21
INi(-) ©
|
1
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!
Pe ie
l
|
[ |
I
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70
|
;
|
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;
{
eee
OO
Oe
HO
—
—O-
3 5 6 8 9 10 13 14
GND
MUTING
Vee
OUT!
OUT2
VEE
6. PACKING
4
Fig.5-4
Equivalent
circuit
of
power
IC
Mark
No.
von °
=
Part No.
AHA-335
ARB-526
ATB-076
ADH-005
AHE-107
iT
[5
GND
@
IN 2(+)
=
IN2(-)
=
|
|
|
|
|
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{
|
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|
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|
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|
pieces
Description
Side pad
Operating instructions
(English)
Loop antenna ssembly
T-type antenna
Packing case

Mees co et pee
Neca an
NSisepane”
7. EXPLODED
Mark
[> [> >
[>
x
No.
sda ade
=
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
Part No.
ANE-410
BBZ30PO80F ZK
ATT-944
PMZ30PO60F MC
AAD-608
VMZ30PO60F MC
NK9SOFUC
AAB-317
NK7OFUC
AAA-084
AAB-316
ANM-293
AAD-607
AAD-606
ASG-541
AAD-605
AEC-784
AXA-373
AEC-471
MTZ30P100FZK
AEK-123
AKP-039
ADG-073
GWM-265
AKN-045
SUJ8LY XSF
ACG-017
BBT3SOPO80FZK
VIEW AND PARTS LIST
NOTES:
e Parts without part number cannot be supplied.
e The A mark found on some component parts indicates the importance of the
safety factor of the part. Therefore, when replacing, be sure to use parts of identical
designation.
e For your Parts Stock Control, the fast moving items are indicated with the marks
ke and x.
tke GENERALLY MOVES FASTER THAN x.
This classification shall be adjusted by each distributor because it depends on model
number, temperature, humidity, etc.
Description Mark No. Part No. Descriptions
Bonnet 50. Speaker switch assembly
Screw (3 x 8) 51. Switch holder
Power transformer (120V) 52. Pully assembly
Screw (3 x 6) 53: LED assembly
Speaker knob 54. Earth
Screw ( 3 x 6) 55. Mounting plate
Nut 56. Pully assembly
Knob B (BASS, TREBLE, 57. Pully assembly
BALANCE) 58. Pully holder
Nut 59. Headphone jack assembly
Tuning knob
60. Chassis
Knob A (VOLUME) 61. Bottom Plate
Front panel assembly 62. Binder
Function knob B (PHONO, 63. Earth terminal
FM, AM) 64. Rear panel
Function knob A (TAPE,
LOUDNESS) 65. Tuning drum
Push switch (POWER) 66. Smoother
67. Pointer holder
Power knob 68. Pointer assembly
Cabinet bumper 69. Heat sink
Tuning shaft
Nylon rivet 70. Wire holder
Screw (3 x 10)
Fuse (T2.5A)
AC socket
AC power cord
Complex assembly
Phone Jack (PHONES)
Speaker switch
Ceramic (0.01)
Screw (3 x 8)
A

AY],
A
|
|
|
|
|
ince of the
: of identical
the marks
is on model
assembly
kK assembly
y