Pioneer SX-939 User manual

<ART-044-0>
SERVICE MANUAL
STEREO RECEIVER
sx-939
KCU, F, GN
NOTE:
MODEL SX-939 COMES IN THREE VaRSIONS DISTINGUISHED AS FOLLOWS:
Round label on
rear panel
Voltage Type
KCU 120V only
F 110V, 120V, 130V
220V and 240V
(switchable) General export model
GN
220V
only
SEMCO
(Sweden),
NEMCO
(Norway)
and
DEMCO (Denmark) approved.
> MPIONEER

Sx-939
CONTENTS
About 220V only model labeled “GN”
This model whose rear panel is labeled “GN” circular mark operates only on 220V,
substantially in its circuit design from two other models. When repairing this model,
please see the manual on page 71 and the followings which include such items as Circuit
connection diagram, Miscellaneous parts list, Schematic diagram of power supply circuit
assembly, P.C. board pattern and its parts list.
Before servicing, also please do not fail to check to see if the “ОМ” mark is labeled on the
rear panel.
12 ESPECIEICANIONSTE S ЧЕ а, а ае pe rano 04 00 2
ZSSIBRONTPANEISPAGIDITIBS En 2 00 14054081 43 ern 5
Boe CONNECTION DIAGRAM v. S ева 7
AZSBBOGK DIAGRAM .... ບ ВЕ ete tele а Ens VER IESUS ЭЭ € enn 9
BRRIGHROUFTIDESERIRTION +... аге А мя ние ае 11
和 12
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82 РАНЛӘТАМЕР:ІСОВОАНЮГОСАШОМ8/72.2...5..55Г2.-7..--5.2...... 14
Э CDIADZGORD:STRINGING: зз эз so. +з ed. ал х I DATI ERG аа 16
10. ALIGNMENT PROCEDURE
ТЛ: EUROS odo nore Ote ala араў аў ара азса гол а
10.2 Germany (Abgleichverfahren)
ТЕ EXBEODEDIVIEWANDIBARTSTELSTE А ranae o Con ER é 20
12. SCHEMATIC DIAGRAMS, P.C. BOARD PATTERNS AND
PARTS LIST
12.1 Circuit Connection Diagram and Miscellaneous Parts
12.2 Tuner Assembly. (AWE:OAT] ee аа аа. າກັນ: ລະເມ
12.3 Muting Circuit Assembly (AWM-063) . . . . . . . . . . . . . . . . . . . ....-..-
12.4 Equalizer Amplifier Assembly (АМЕ-013) ........................
12.5 Control Amplifier Assembly (AWG-027) . . . . . . . . . . . . . . . . ........-
12.6 Power Amplifier Assembly (AWH-030) . . . . . . . . . . . . . . . . . . . . .......
12.7 Protection Circuit Assembly (AWM-062) . . . . . . . . . . . . . . . . - . . . . . . . .
12.8 Power Supply Circuit Assembly (AWR-052)
12.9 Switch Circuit Assembly (AWS-064) . . . . . . . . . . . . . . . . . . . . .....--...-
12.10 Switch Circuit Assembly (AWS-065) . . . . . . . . . . . . . . . . . . . . . . ....... 61
12.11 Switch Circuit Assembly (АМ/5-066).... 3102
12.12 Switch Circuit Assembly (АМ/5-067)............................. 64
12.13 Switch Circuit Assembly (AWS-068) . . . . . . .. . . .. . . . .. . . . . . . . . . . . . . . 66
12.14 Switch Circuit Assembly (АМ/5-069)............................. 67
12:15 БР Connector Assembly (АМ/Х-062).. 22505... . . . . . . . . . . . . . . . . . -:- 69
13. PACKING METHOD AND PART NUMBERS .. . . . . . . . . . . . . . ...........- 70
14. SCHEMATIC DIAGRAMS, P.C. BOARD PATTERN AND
PARTS LIST FOR 220V ONLY MODEL
14.1 Circuit Connection Diagram and Miscellaneous Parts ................ 71
14.2 Power Supply Circuit Assembly (AWR-056) ....................... 76

1. SPECIFICATIONS
SEMICONDUCTORS
FETs ..
157
Transistors . ກຕ
let DERE EUIS
AMPLIFIER SECTION
Continuous Power Output
20Hz~20kHz
(Both channels driven)
1kHz (Both channels driven) .
Harmonic Distortion
(20Hz~20kHz Continuous
Power Output) ...
(1W + 1W, Power Output) ..
Intermodulation Distortion
(Continuous Power Output) ..
(1W + 1W, Power Output)...
Power Bandwidth
(IHF, Both channels driven) ..
Frequency Response ....
Input Sensitivity/Impedance
г. ТОМ + 70W (82), 80W + 80W (49)
-.75М/ + 75W (80), 100W + 100W (49)
Less than 0.3%
-. Less than 0.05%
... Less than 0.3%
.. Less than 0.05%
.5Н2-40КН: (T.H.D. 0.3%)
... 7Hz~100kHz
POWER -AMP IN s аа 1V/50k%
Output
ເ ена ал ау d .:....А, В, C, + 8, A + C, В + C (49-160)
FAG ARISTON гае 49-169
Damping Factor
О : ພະ ເສາ More than 45
Hum & Noise
(IHF, short-circuited,
ອເຕ ເພ ະມີ. More than 110dB
Residual Hum & Noise
(80, Pre & Power amplifier) ........... Less than 1mV
PREAMPLIFIER SECTION
Input Sensitivity/Impedance
ВЫВМО 1. ды озан о ໃ“ 2? 2.5mV/50kQ2
PHOND OI х хай E Н 2.5mV/50k22
PHONO Overload Level
(rms/p-p) .. ... 250mV/700mV
MIC ... .-..2.0ту/50к0.
» 150mV/70kQ.
150mV/70kQ
150mV/70kQ
TAPE PB 1, 2.
TAPE PB 2(DIN connector)...
Output Level/Impedance
TAPE RECA, 2 аза nme 150mV
ТАРЕ REC 2 (DIN connector) ....... 30mV/80kQ
PRE OUT + 1V/1kQ.
Harmonic Distortion
ТООН ОКНЕ J uu, 2272 Less than 0.1%

Frequency Response
PHONO (RIAA equalization) .
AUX, TAPE PB
Tone Control
BASS:
MAIN
SU8....
TREBLE:
MAIN.
SUB"...
Filter
LOW Cut ..
HIGH Cut ....
Loudness Contour
(Volume control set at
—40dB position) ............................ +8dB (100Hz), +4dB (10kHz)
Hum & Noise
(IHF, short-circuited, A
Network)
PHONO .
MIO
AUX, TAPE PB . More than 95dB
.. 30Hz~15kHz+0.3dB
- 10Hz~40kHz* 9 dB
.. —8dB (50Hz) 6dB/oct.
.. —9dB (10kHz) 6dB/oct.
FM SECTION е
Usable Sensitivity (IHF) ..................... 1.8uV
Capture Ratio (IHF)
Selectivity (IHF)..
Signal-to-Noise Ratio ..
Image Rejection (98MHz) . . 85dB
IF Rejection (98МН2) ... 100dB
Spurious Rejection.. 100dB
AM Suppression ...
Harmonic Distortion:
МОМО ere Sp ris ree FOVEO RR Less than 0.296
STEREO .. Less than 0.4%
*0.2
Frequency Response .
.. 20Hz~15kHz- 2:0 dB
50Hz~10kHz*9-2 dB
Stereo Separation:
ТЕМ vise າ, teen c aen on КК More than 40dB
50Hz~10kHz .. More than 30dB
Sub Carrier Suppression . .. 65dB
.. 3009 Balanced, 7502 Unbalanced
„ ON-OFF
Antenna Input ..
Muting

SX-939
AM SECTION
Sensitivity
(IHF,
Ferrite
antenna)
....................
300uV/m
(IHF,
Ext.
antenna)
....
1Би\/
Selectivity
...
40dB
.50dB
.65dB
.85dB
Signal-to-Noise Ratio
Image Rejection...
IF Rejection ...
MISCELLANEOUS
Power Requirements ...
AC
120V
60Hz
or
110,
120,
130,
220
and
240V
(switchable)
50/60Hz
290W (UL approved model only)
470W
(5
line
voltage
model
only)
ໃາ
ЦОО
022
520
(W)
х
175
(H)
х
420
(D)
mm
20-1/2 x 6-7/8 х 16-9/16 in.
Power Consumption .
Weight:
Without Package
With Package
FURNISHED PARTS
FM T-type Antenna
Operating Instructions .
Fuse 6A ....
Fuse 3A ....
... 18.5 kg (40 Ib 11 oz)
2.22.6 kg (49 Ib 12 oz)
1
«1
i (5 line voltage model only)
NOTE:
Specifications
and
the
design
subject
to
possible
modification
wi:
thout
notice
due
to
improvements.

2. FRONT PANEL FACILITIES
FRONT PANEL FACILITIES
SPEAKER BUTTONS
Each of speaker systems A, B, and С is connected to each
of output terminals A, B, and C.
By pushing the following:
SPKR-A .... Speaker systems A into operation
SPKR-B .... Speaker systems B into operation
SPKR-C .... Speaker systems C into operation
NOTES:
1. When any two pairs of the buttons (A + B. B + C, C + AJ are
depressed, the corresponding pairs of speaker systems will
come into operation. However, operating all three buttons
even though depressed at the same time is not possible.
Only when listening through headphones, press again the
SPKR button(s) in’ use to OFF (undepressed) from the
ON position (pressed)
POWER SWITCH
Turn this switch ON but wait for some 3 to 6 seconds,
during the silence of which the protection circuit climi-
nates the unpleasant noise not imputed to a receiver fault
PHONES (1, 2) OUTPUT JACKS:
Accept two pairs of headphones.
BASS CONTROLS
Adjust bass tone quality.
10082 4.4 .5 For the low frequencies below 400Hz.
Possible up to 1048 of increasing or
reducing at 100Hz in 2dB steps.
БОН бы After adjustment by the 100Hz control,
further adjust frequencies below 80Hz by
this control, if necessary. Possible up to
5dB of increasing or reducing in bass
response at 50Н2 in 2.5dB steps.
LOW CUT, HIGH CUT BUTTONS:
LOW ...... When the low-pitched rumble (turntable
motor or other source) is obtrusive, de-
press the LOW CUT button to ON. In no
interference, leave it undepressed (OFF).
HIGH ...... When the high frequency scratch noise
(records or other source) is much, depress
this button to ON. In no interference,
leave it undepressed (OFF).
TONE SWITCH
When in the ON (up) position, this switch causes the
атр ег section to operate with a flat frequency regard-
less of the tone control settings. Use this switch to check
the audio characteristics of your listening room such as
when it is necessary to check the tone quality of phono
cartridges and speakers and also to particularly set the
tone controls to be assessed.
SIGNAL METER
For AM and FM station tuning.
AM tuning: Tune the dial pointer so that the SIGNAL
meter needle comes to the extreme right.
FM tuning: Both the SIGNAL and FM TUNING
meters work together. The optimum
point of the SIGNAL meter needle is the
same as in AM tuning. Then use the FM
TUNING meter.
FM TUNING METER
While getting the SIGNAL meter needle going to the right,
make fine adjustment with the FM TUNING meter whose
needle comes to the center (indicating the optimum
reception).
FM STEREO INDICATOR
TUNING KNOB
TREBLE CONTROLS
Adjust treble tone quality.
10KHz . . . . For the high frequencies above 2.5 kHz.
Possible up to 10dB of increasing or
reducing in treble response at 10КН2 in
2dB steps.
WEH . . . . After adjustment by the 10KHz control,
further adjust frequencies above 12k Hz
by this control, if necessary. Possible up
to 5dB of increasing or reducing in treble
response at 20k Hz in 2.5dB steps.
AUDIO MUTING BUTTON —20dB
Depress this button to mute the audio input to —20dB.
No need to turn down the VOLUME control on each
occasion for your convenience
TAPE DUPLICATE SWITCH
Leave this switch in the ON (down) position to duplicate
or cdit a recorded tape using two tape decks. For normal
use, switch over to the OFF (up) position.
BALANCE CONTROI-
Adiusts the balance between the sound volume from the
left and right speaker systems.
--ТАРЕ MONITOR (1, 2) SWITCHES
Monitor the recorded sound while recording with a tape
deck. Also possible to play back tapes as follows:
B With a tape deck connected to the TAPE
1 jacks (REC and PB), either monitoring
of recording in progress or playing back is
possible.
ມ. ыс With a tape deck connected to the TAPE
2 jacks (REC and PB or REC/PB con-
nector), the same as in 1 above is possi-
ble.
DOLBY NR ADAPTOR SWITCH
When employing Dolby Noise Reduction Adaptor
depress this DOLBY NR ADAPTOR to ON.
FUNCTION SELECTOR BUTTONS
For selecting the program source, push each button 35
follows:
AM . . For AM broadcast reception.
FM . For FM broadcast reception. The
STEREO indicator lights up when the
broadcast is in stereo.
PHONO 1 ... For operating a turntable connected to
the PHONO 1 input jacks.
PHONO2 ... For operating a turntable connected to
the PHONO 2 input jacks.
MIC ....... For using a microphone. Not possible to
mix with other program source.
AUX ...... For listening to audio equipment (car-
tridge tape player, TV sound tuner, etc.)
connected to the AUX input jacks.
DIMMER SWITCH
Dims the brightness of the indicator light. Press again to
restore full brightness.
FM MUTING BUTTON
Leave this button undepressed (in the ON position) while
tuning in FM stations. Inter-station noise may interfere
with FM reception while tuning between stations. To
suppress this noise, leave the MUTING button undepress-
ed (in the ON position). If the low signal strength is due
to distance from the transmitter or other influences,
depress this button, at which the weak station will be
heard with the MUTING “OFF.”
LOUDNESS BUTTON
Depress this button to listen at low volume. The human
ear's frequency response varies according to the listening
volume. The depressed button compensates for hearing
response with emphasis on the bass and treble.
MIC INPUT JACKS
ke ба For connecting the left and right channel
microphones,
NOTE:
Use the high impedance (above 20k9) with 6mm diam, phone
plugs.
VOLUME CONTROL
Governs both the volume of sound outputs from the
speaker systems and from the headphones.
MODE BUTTON
Leave this button undepressed (if. necessary, depress this
to release it when already depressed) for STEREO
playback. For MONO playback, depress it. In this case
stereo signals for left and right channels will be mixed into
mono signal which will be heard from the center of both `
speaker systems.

3.
CONNECTION
DIAGRAM
TYPE
OUTDOOR
TAPE
DECK
TAPE
DECK
FM
ANTENNA
ЕМ
ANTENNE
AM
ANTENNA
TURNTABLE
TURNTABLE
CARTRIDGE
(open-reel,
cassette)
TAPE
PLAYER
1
ນຫ
=
воб
ຫ;
тй
гоч
LINE LINE
LINE
LINE
p
c
to
INPUT
OUTPUT
INPUT
OUTPUT
ground
terminal
of
turntables,
tape
decks,
etc.
3002
feeder
1
l
lE
I
ІІ
ТШ
2
2
deem
ee
eee
75
І
coaxial
|
Recording
/
Playback
cord
cable
DIN-type
FM DE-EMPHASIS SWITCH
| In some countries, the receiver
is delivered with a selector switch
for adjusting the FM de-emphasis
from 50 to 75 sec. If your unit
is equipped with such a switch
on the rear panel, and if the high
| sound range gives an impression
of weakness move the de-em-
phasis switch to its other posi-
tion.
L
e
@
|
vai
ຢຢ
|;
•
їе
Е
2
(“ocr
comms
|
ແ.
коер
| е
L t
| © |
| |
AM FERRITE ANTENNA
For comeing) Lor
4-channel discrete
FM adaptor
For connecting (P
Dolby NR adaptor x
ху
FUSE
PRE/POWER AMP
The bridge/connecting plugs
between PRE OUT and POWER
IN jacks should always be left in
position in normal use. If they
are
disconnected
or
removed,
no
©
e
e
©
©
©
©
©
-一
-一
sound
will
come
from
the
speak-
:
© ©
ers.
Always be sure to cut the power
supply before attempting to re-
move them.
RIGHT LEFT RIGHT LEFT RIGHT LEFT
(B)
SPEAKER SYSTEMS

4. BLOCK DIAGRAM
4CH MPX QUT
r=
©
RF
amplifier
Mixer
IF
amplifier
Detector
|
өӨӨӨНӨӨӨ
БН
ТӨӨГ--
=
METER
s]
—
SIGNAL
:
ор
te
Stabilizer
Separation
Low
pass
filter
Н
ў
Sie
to
Tuner
<
Local
oscilator
control
&
АҒ
amplifier
520
gue
Pilot Lamps
+
MPX decoder
(> AM tuner
—
FUSE
to
AF section.
te
uem
AC
LINE
21
522
ао
MUTING SWITCH
Power transformer
to Power amplifier
Stabilizer & Regurator
Sua Sisa $60
[一 2
©©©
Equalizer amplifier
Protection circuit
ә ә. 3
sup 95% De
Buffer
omplifier
Subtone
Main
tone
Control_amplifier
RIGHT CHANNEL | LEFT CHANNEL
SWITCHES =
51 FUNCTION AM TONE DEFEAT
5? + FM LOW FILTER
53 4 PHONO 1 HIGH FILTER
34 ж. PHONO 2 AUDIO MUTING
$s “ МІС SPEAKER А
56 + AUX a B
57 DUPLICATE ”
Ss TAPE MONITOR 1 DIMMER
59 TAPE MONITOR 2 POWER
$10 NR ADAPTOR 5 FM MUTING
Sn MODE
512 LOUDNESS

5. CIRCUIT DESCRIPTION
SIGNAL PATH
1. The FM broadcast signal waveform from the
antenna is fed to the two dual-gate MOS
field-effect transistor in the front end sec-
tion for radio frequency amplification. This
signal is converted into an intermediate fre-
quency by the dual-gate MOS FET mixer
stage in combination with the signal from
the local oscillator.
2. The intermediate frequency signal, con-
verted within the front end section, is fed to
three ceramic filters and two ICs, where it is
tuned, amplified, and detected, becoming a
audio frequency (composite) signal.
The composite signal following detection is
fed to the 4 CH MPX terminal jack and the
multiplex decoder stage.
8. The multiplex decoder stage uses one IC for
three functions: to demodulate the com-
posite signal into the left and right channel
stereo signals, to operate the automatic
mode switching between stereo/mono, and
to switch the stereo indicator lamp appro-
priately.
The decoding system uses a phase locked
loop (PLL) circuit, which assures continuous
stable operation and excellent stereo sepa-
ration with low susceptibility to external
noise (such as car ignition noise) and am-
bient temperature changes.
After decoding, the signal is fed to four
transistors and one LC filter, where the
residual carrier component (38kHz, 19kHz,
and SCA) is rejected, and then to the audio
amplifier section.
4. The FM muting circuit consists effectively of
two circuits, designed to reduce the pulse
noise which can so easily arise when a
muting circuit is operative.
The one circuit is an electronic switch in-
corporated into the IC, so that the de-
modulated circuit is switched off and on in
the IC, and the other gate circuit the com-
posite signal by means of an FET.
5. The AM tuner section employs one mono-
lithic IC which functions as radio frequency
amplifier, frequency converter, local oscil-
lator, intermediate frequency amplifier, and
detector. The output is a pure audio signal.
6. The signals which are applied to the MIC and
PHONO terminal jacks are selected by the
FUNCTION switch before being fed to the
first stage of the three-stage differential
direct-coupled equalizer amplifier by which
the signals are amplified.
In order to reduce the switch noise, the
circuit configuration employed enables the
potential at the input and output terminals
to be set at near zero volts.
10.
alls
12.
SX-939
It incorporates an independent differential
circuit in the first stage of the equalizer
amplifier whose DC supply uses twin plus
and minus.
. The output from the equalizer amplifier,
together with that from the AUX terminal
jacks, the audio signal from the AM tuner,
and the audio signal from the FM tuner, are
all selected by the FUNCTION switch, and
pass through the switch circuit for TAPE
DUPLICATE, TAPE MONITOR, DOLBY
NR ADAPTOR, and the circuits for
BALANCE and VOLUME controls, before
being fed to the control amplifier.
. The control amplifier has an extremely high
input impedance, using PNP and NPN tran-
sistors in a two-stage direct-coupled circuit.
This greatly reduces the influence of the
performance inherent in equipment con-
nected externally.
The output from this two-stage direct-
coupled circuit is divided into two circuit
systems.
One goes to the TONE switch via the twin
tone control circuit, and the other goes
directly and unmodified in any way to the
TONE switch. The TONE switch selects
between them.
. The amplifier section of the twin control has
closed loop NFB amplifiers for both the
main and sub circuits, each of which has its
own transistor, eliminating mutual inter-
ference,
The control amplifier output is fed to the
power amplifier after passing through the
LOW FILTER, HIGH FILTER, and AUDIO
MUTING circuits.
The first stage of the power amplifier is a
differential amplifier element, and the
second stage uses a constant current load
circuit, so that DC potential drift is pre-
vented.
On the other hand, the final output stage
uses two power transistors in parallel in both
the upper and lower circuits, so that large
collector dissipation is possible.
The power amplifier output is fed to the
three push buttons which form the
SPEAKER switch. This selects A, B, and C
speaker system terminal connection.
If all three speaker systems were to be
connected simultaneously, the effective
speaker impedance might be less than 40.
To guard against this possibility, when all
three buttons are depressed together, all
three systems are disconnected from the
amplifier.
The protection circuit which guards against
DC potentials at the power amplifier output
junctions, against speaker complex load im-
11

pedances less than 49, and shorts across the
speaker terminals. Their operation is such
that, under the corresponding abnormal con-
dition, a relay acts to separate the output
junction and the output circuit. Further,
this protection circuit also helps to mute
the unwanted signal which immediately
follows switching the POWER switch ON,
and to immediately disconnect the output
after switched OFF.
6. LEVEL DIAGRAM
AUX
PHONO 7
MIC I EQUALIZER ເມ ເມ CONTROL
| AMP 2 = AMP
21:2
ao
a>
Low 8
HIGH FILTER
SPEAKERS
POWER AMP
HEADPHONES
П
|
|
!
!
|
|
І
|
1
|
|
|
|
|
1
30
SPEAKERS
28V/80 (98W)
|
|
|
|
|
|
1
|
|
|
1
|
|
|
|
|
1
|
|
|
I
|
Ї
!
l
1
|
|
|
|
(0 dBV=1V)
HEADPHONES
15V
dBV
IN
LEVEL
-60
FREQUENCY AT kHz
12