Pioneer SX-939 User manual

<ART-044-0>
SERVICE MANUAL
STEREO RECEIVER
KCU, F, GN
NOTE:
MODEL SX-939 COMES IN THREE VERSIONS DISTINGUISHED AS FOLLOWS:
Round label on
rear panel
Voltage
Type
KCU 120V only
UL (U.S.A.) and CSA (Canada) approved.
F
110V, 120V, 130V
220V and 240V
(switchable)
General export model
GN
—
220V only
SEMCO (Sweden), NEMCO (Norway) and
DEMCO (Denmark) approved.
<74B02M61D> CD PIONEER

SX-93 9
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 "GN" mark is labeled on the
rear panel.
1. SPECIFICATIONS. 2
2. FRONT PANEL FACILITIES . 5
3. CONNECTION DIAGRAM . 7
4. BLOCK DIAGRAM . 9
5. CIRCUIT DESCRIPTION .11
6. LEVEL DIAGRAM .12
7. DISASSEMBLY .13
8. PARTS AND P.C. BOARD LOCATIONS.14
9. DIAL CORD STRINGING.16
10. ALIGNMENT PROCEDURE
10.1 English.17
10.2 Germany’(Abgleichverfahren) .79
11. EXPLODED VIEW AND PARTS LIST.20
12. SCHEMATIC DIAGRAMS, P.C. BOARD PATTERNS AND
PARTS LIST
12.1 Circuit Connection Diagram and Miscellaneous Parts .27
12.2 Tuner Assembly (AWE-041).32
12.3 Muting Circuit Assembly (AWM-063). 38
12.4 Equalizer Amplifier Assembly (AWF-013).40
12.5 Control Amplifier Assembly (AWG-027) . 43
12.6 Power Amplifier Assembly (AWH-030). 48
12.7 Protection Circuit Assembly (AWM-062). 53
12.8 Power Supply Circuit Assembly (AWR-052) . 56
12.9 Switch Circuit Assembly (AWS-064). 59
12.10 Switch Circuit Assembly (AWS-065). 61
12.11 Switch Circuit Assembly (AWS-066). 62
12.12 Switch Circuit Assembly (AWS-067). 64
12.13 Switch Circuit Assembly (AWS-068). 66
12.14 Switch Circuit Assembly (AWS-069). 67
12.15 5P Connector Assembly (AWX-062). 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 .
ICs .
Transistors.
Diodes .
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
POWER AMP IN.
Output
Speaker .„....
Headphone .
Damping Factor
(1kHz, 80) .
Hum & Noise
(IHF, short-circuited,
A Network).
Residual Hum & Noise
(80, Pre & Power amplifier).
PREAMPLIFIER SECTION
Input Sensitivity/Impedance
PHONO 1 .
PHONO 2 .
PHONO Overload Level
(rms/p-p).
MIC .
AUX.
TAPE PB 1,2.
TAPE PB 2 (DIN connector).
Output Level/Impedance
TAPE REC 1, 2 .
TAPE REC 2 (DIN connector).
PRE OUT.
Harmonic Distortion
(20Hz~20kHz).
3
4
57
39
70W + 70W (80), 80W + 80W (40)
75W + 75W (80), 10OW + 10OW (40)
Less than 0.3%
Less than 0.05%
Less than 0.3%
Less than 0.05%
5Hz~40kHz (T.H.D. 0.3%)
7Hz~100kHz
1 V/50kO
A, B, C, A + B, A + C, B + C (40-160)
40-160
More than 45
More than 110dB
Less than ImV
2.5mV/50kO
2.5mV/50kO
250mV/700mV
2.0mV/50kO
150mV/70kO
150mV/70kO
150mV/70kO
150mV
30mV/80kO
1 V/lkO
Less than 0.1%
2

Frequency Response
PHONO (RIAA equalization)
AUX, TAPE PB.
Tone Control
BASS:
MAIN .
SUB.
TREBLE:
MAIN.
SUB.
Filter
LOW Cut .
HIGH Cut.
Loudness Contour
(Volume control set at
—40dB position) .
Hum & Noise
(IHF, short-circuited, A
Network)
PHONO .
MIC .
AUX, TAPE PB .
Muting.
FM SECTION
Usable Sensitivity (IHF) .
Capture Ratio (IHF).
Selectivity (IHF).
Signal-to-Noise Ratio.
Image Rejection (98MHz).
IF Rejection (98MHz) .
Spurious Rejection.
AM Suppression.
Harmonic Distortion:
MONO .
STEREO .
Frequency Response .
Stereo Separation:
1kHz .
50Hz~10kHz .
Sub Carrier Suppression.
Antenna Input.
Muting.
30Hz~15kHz±0.3dB
10Hz~40kHz+° dB
±10dB (100Hz)
±5dB (50Hz)
±10dB (10kHz)
±5dB (20kHz)
—8dB (50Hz) 6dB/oct.
—9dB (10kHz) 6dB/oct.
+8dB (100Hz), +4dB (10kHz)
More than 70dB
More than 65dB
More than 95dB
—20dB
1.8juV
I.OdB
80dB
70dB
85dB
lOOdB
lOOdB
55dB
Less than 0.2%
Less than 0.4%
20Hz~15kHz-°:o dB
50Hz~10kHz!g § dB
More than 40dB
More than 30dB
65dB
300S2 Balanced, 75JT2 Unbalanced
ON-OFF
3

SX-939
AM SECTION
Sensitivity
(IHF, Ferrite antenna).300/iV/m
(IHF, Ext. antenna) .15 /jV
Selectivity.40dB
Signal-to-Noise Ratio.50dB
Image Rejectioa.65dB
IF Rejection.85dB
MISCELLANEOUS
Power Requirements .AC 120V 60Hz or 110, 120, 130, 220 and 240V
(switchable) 50/60Hz
Power Consumption.290W (UL approved model only)
470W (5 line voltage model only)
Dimensions.520 (W) x 175 (H) x 420 (D) mm
20-1/2 x 6-7/8 x 16-9/16 in.
Weight:
Without Package.18.5 kg (40 lb 11 oz)
With Package.22.6 kg (49 lb 12 oz)
FURNISHED PARTS
FM T-type Antenna . 1
Operating Instructions . 1
Fuse 6A.i -I
Fuse 3A. 1 1 (5 line voltage model only)
NOTE:
Specifications and the design subject to possible modification without notice due to improvements.
4

2. FRONT PANEL FACILITIES
FRONT PANEL FACILITIES
SPEAKER BUTTONS-
Each of speaker systems A, B, and C 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 pain of the buttons (A * B, R * C, C * A) 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.
2. Only when listening through headphones, press again the
SPUR hut ton/s) in use to OEE (undepressed) from the
ON position /pressed)
POWER SWITCH-
Turn this switch ON but wait for some 3 to 6 seconds,
during the silence ol which the protection circuit elimi¬
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.
100Hz.For the low frequencies below 400llz.
Possible up to lOdB of increasing or
reducing at 100Hz in 2dB steps.
50H/.Alter adjustment by the 100Hz control,
further adjust frequencies below 80Hz by
this control, il necessary. Possible up to
5dB of increasing or reducing an bass
response at 50Hz 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
amplilier section to operate with a flat frequency regard¬
less of the tone control sellings. 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.
4
fi¬
ll i'M 92 94 . 96
TREBLE CONTROLS- 1
Adjust treble lone quality.
lOKHz.For the high frequencies above 2.5kHz.
Possible up to lOdB of increasing or
reducing in treble response at lOKHz in
2dB steps.
20KHz.After adjustment by the 10kH/ control,
further adjust frequencies above 12kHz
by this control, if necessary. Possible up
to 5dB of increasing or reducing in treble
response at 20kHz 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 edit a recorded tape using two tape decks. For normal
use, switch over to the OF F (up) position.
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-,
m a
u
« , * i _ _
M
4 ^
M
=
*
? f ‘
v‘
f ^
1
}
-•
-• -
h
BALANCE CONTROL—*
Adjusts the balance between the sound volume from the
left and right speaker systems.
-TAPE MONITOR (1, 2) SWITCHES
Monitor the recorded sound while recording with a tape
deck. Also possible to play back tapes as follows:
1 . W ith a tape deck connected to the TAPE
1 jacks (REC and PB), cither monitoring
of recording in progress or playing back is
possible.
2 . W ith 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 as
follows:
AM.For AM broadcast reception.
FM .For FM broadcast reception. The
STEREO indicator lights up when the
broadcast is in stereo.
PHONO I . . . For operating a turntable connected to
the PFIONO 1 input jacks.
PHONO 2 . . . 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
L, R.For connecting the left and right channel
microphones.
NOTE:
Use the high impedance (above 20ksi) 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.

CONNECTION DIAGRAM
AM FERRITE ANTENNA
For connecting
4-channel discrete
FM adaptor
For connecting
Dolby NR adaptor
FM DE-EMPHASIS SWITCH-
In some count'ies, the receiver
is delivered with a selector switch
for adjusting the FM de-emphasis
from 50 to75/Jsec. 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.
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
sound will come from the speak¬
ers.
Always be sure to cut the power
supply before attempting to re¬
move them.
RIGHT LEFT
(C)
SPEAKER SYSTEMS

4. BLOCK DIAGRAM

SX-939
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.
3. 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.
It incorporates an independent differential
circuit in the first stage of the equalizer
amplifier whose DC supply uses twin plus
and minus.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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 4n.
To guard against this possibility, when all
three buttons are depressed together, all
three systems are disconnected from the
amplifier.
12. The protection circuit which guards against
DC potentials at the power amplifier output
junctions, against speaker complex load im-
11

pedances less than 4n, 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.