Pioneer SX-3700 User manual

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STEREO
RECEIVER
sSx-37cIcI
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MODELSX-3700
COMES
INFOURVERSIONSDISTINGUISHEDASFOLLOWS.
Typ. Voltag. Ramarks
KU 120Vonly U.S.A.model
KC '| 20V only Can€damodel
11OV
, 12OV ,22OV, end24OV
(Switchabls) Gen€ral exDort model
11OV
. 12OV
,22OV , and240V
(
Switcha
ble) U.S.Military mod6l
e This servicemanualis applicable
to the SX-3700/KU. For servicingof the othertypes,please
refer
to theadditionalservicemanual.
CONTENTS
1. SPECTF|CATTONS
...........
2. FRONT PANELFACILITIES
. , . .
3. BLOCKDIAGRAM
4. CIRCUITDESCRIPTIONS
4.1 FMTuner
4.2 AM Tuner
4.3 Display
Circuit. .
4.4 Equalizer
Amplifier
. . . . . . .
4.5 ToneControlAmplifier . . . .
4.6 PowerAmplif
ier.. .... ...
4.7 PowerIndicator
Circuit.. -.
4.8 Protection
Cirorit . . . . . . -.
5. DISASSEMBLY ......
6. PARTS
LOCATION
2
..4
..6
..8
. 11
. 11
. 11
. 11
. 11
. 13
.14
17
18
19
19
21
za
30
34
J5
41
7. DIAL
CORD
STRINGING
8. ADJUSTMENTS
8.1 FM Tuner
8.2 AM
Tuner
8.3 ldle CurrentAdiustment
8.4 FL IndicatorCircuit
... -.......
9. SCHEMATICDIAGRAMS,P,C.BOARD
CONNECTIONDIAGRAMAND
PARTS
LIST
9.1 Schematic
Diagram
.
9.2 P.C.BoardConneaionOiagram
. . .
......16
l'
9.3 PansList.....
1O. PACKING
11. EXPLODEOVIEW....
12. ADDITIONAL
SERVICE
MANUALSX.82O l

six-37C'c'
1.
SPECIFICATIONS
Amplifier
Section
Continuous
power
outputof
45watts-
per
chan.
nel,
min.,
at
8
ohms
from
20Hertz
to 20,000
Hertzwithn0more
than0.0?%
total
harmonic
distortion.
Total
Harmonic
Oistortion
(20
Hertzto 20,000Hertz.
8ohms,
from
AUX)
continuous
rated
Dower
outout . . Nomorethan0.02%
22.5
watts
per
channel
power
output
...... Nomorethan0,02%
Intermodulation
Distortion
(50
Hertz
:7,0O0Henz
=
4 : 1,8ohms,
from
AUX)
continuous
rated
oower
output . . Nomorethan
0.02%
22,5watts
per
channel
power
output
...... Nomorethan0.02%
Damping
Factor
(20
Hertzto 20,000Hertz,
S
ohms)
,"o,irs"",i,i"'ir),;;";;;";;
""
PHONO
. 2.5mV/50kilohms
AUX,TAPEPLAY1,2
.......'l50mv/50kilohms
Phono
OverloadLevel
(T.H.O.0.02%,
1,000H2)
PHONO.
Output
TAPEREC1,2 -.. .
Speaker .
FrequencyResponse
PHONO
(R
IAA Equalization)
250mV
l50mV
A,B,A+B
AUX,TAPE
PLAY
1,
2
ToneControl
BASS
,,.
TREBLE.
SubsonicFilter
. . 20Hzto 20.000H2
10.2d8
. . . lOHztoIOO,OOOHZ]]dB
..... iSdB
(100H2)
..... iSdB
(10,000H2)
..... 15Hz
(-tuB/oct)
LoudnessContour
(Volume
controlsetat -40d8 position)
...... +6dB{100H2)
HumandNoise
(lHF,short-circuited.
A network)
PHONO
. ........79d8
AUX,TAPEPLAY1.2,. ..... 95dB
400kHz.
StereoSeparation
Distortion
(at
65dBf)
MONO l00Hz........
1kH2.........
6kHz.........
STEREO
,IOOHZ
1kHZ.........
6kH2.........
CaptureRatio
AlternateChannelSelectivity
o.'t70
o.o7./"
0.15%
o.2y,
o.15%
o.25%
1.ft8
75d
B
.45d8
.35d8
. 2OHztolskHz]3
3dB
. 65dB
.65d8
.90d8
.55dB
. 50dB
.65dB
. 19.2dBf
(spv)
. 300
ohmsbalanced,
75
ohmsunbalanced.
A
t
lkHz
30Hzto l5kHz
FrequencyResponse
.
SpuriousResponseRatio
..... .
lmageResponse
Ratio... . . .,.
lF ResponseRatio . . .
AN4SuppressionRatio.
.. . . ...
SubcarrierProductRatio.. . . . .
SCARejectionRatio. .. . . . . . .
MutingThreshold
Antenna
Input
AMTuner
Section
Sensitivity
(lHF, FerriteAntenna)
(lHF,
Ext.
antenna). .
Selectivity
Signal-to-NoiseRatio....... ..
lmage
BesponseRatio,.... ...
lF ResponseRatio . . .
Antenna.
. 300rrV/m
.. 15pV
.. 27dB
. . 52dB
. . 32dB
. . 40d8
Ferriteloopstickantenna
,A
A
FMTuner
Section
Usable
Sensitivity
(lHF)
. . .
50dB
OuietingSensitivity
MONO
..
STEREO
.
Signal-to-NoiseRatio
t\40No . .
STEREO,
10.3dBf
(1.8pV)
15dBf
(3.1l]V)
37dBJ
(39pV)
80dB
{at
65dBf)
75dB
(at
85dBf)
Miscellaneous
Power
Requirements
.......... AC120V.60H2
PowerConsumption
... ..... 290W(UL)
Dimensions .. 480(W)x 145(H)x364(D)mm
18-14/16(W)
x 5-11/16{H)
x 14-5l16(D}in
Weight
(without
package)
FurnishedParts 11.6k9
{25
lb9oz)
Operatinginstructions...,,.... 1
FMT-typeantenna
........... 1
*Measured pursuant to the Federal Trcde commission's Trade
Regulation tule on Power Output Claims for Amplifie6.
NOTE:
Specifications and the design subject to possible modifications
without notice due to improvements.
A

2.FRONT
PANEL
FACILITIES
O PowER
swrrcH
Set this switchto ON to supply
powerto the receiver.
Therewill bea short delay
whenit issetto ON.because
the muting circuit has been actuated
to suppressthe
unpleasant
noisethat is sometimes
generated
whenthe
power
is
switchedonandoff.
@ SPEAKER
swITcHEs
Depressthe switchcorrespondingto the speakerscon-
nectedto theSPEAKERSterminals
(A or B) on the rear
panel.
You candepressboth of thesebuttonsto listen
to the
soundfrom two pairs
oi speakersystemsat the same
time.
@ POWER
METER
This meter
allows
you to read
out the rated
power
level
on the fluorescentdisplay
tube when speakerswith a
nominal impedance
of I ohms are connectedto the
speakerterminals.
O DIAL POINTER
This
pointer
indicatesthebroadcasting
stations.
@ ouARTz
LocKEDrNDrcAToR
This indicator
lightsup after the optimumtuning
point
has
beenobtained
and
displays
that the receiving stateis
stabilizedbvthe
built-inouartzlockcircuit.
@ FM STEREOINOICATOR
This indicator lights up when receiving
an FM stereo
program.
@ SIGNAL
INDtcAToR
This indicatorlights
in sequence
from left throughright
during
the tuningof an AM or FM broadcastin accord-
ance with the strengthof the signalsbeing received.
The optimum tuning point is where the maximum
numberof indicatorslight.
@ TUNINGINDICAToR
Whentuning in an FM station.
the optimum reception
point is indicated
when the centerindicator lights
up.
When the left indicatorhascomeon, rotate
the tuning
knob slightlyclockwise.Whenthe rightindicator
comes
on.rotate theknob slightlycounterclockwise.
@ FREOUENCY
DISPLAY
Thisindicatesthefrequencywhichistuned. T
With FM reception,
the letters
"FM" appearon the left
of the displayand "MHz" on the right.WithAM recep-
tion. "AlV" appears on the left and"kHz" on the right.
These changewhen the function selector
position is
changed.
@ TUNING
KNOB
Use
this
knob
to tuneinto broadcastinq
stations.
O HEADPHONES
JACK
Plugthe headphones
into this jack when you want to
listenthrough
yourstereoheadphones.
Releaseboth speakerswitchesii you want to listento
the
soundthrough
your
headphones
only.

]^
.r.
\A
FM:
AM:
AUX:
PHONO:
a
q}'..
@ BNSSANDTREBLE
coNTRoLS
Usethesecontrolsto adjustthebass
andthetreble.
lf you
turn the basscontrolto the right from itscenter
{0)posi-
tion, you will beableto emphasizethe soundinthe low-
frequencyrange.Conversely,
turningthis control to the
left from thecenter
(0)
position
willattenuatethe
sound.
You canusethetreble
controlto adiust thesound
in
the
high-trequencyrange.
@ LOWFILTER
SWITCH
Whenthis switchissetto 'lsHz.a 6dB/oct attenuation
canbeprovided
for frequencies
below15H2.Thismeans
that you cancancelout noiseintheultra-lowfrequencies
which is generated by low-pitchedrumblefrom a turn-
tableandother formsof distortion.Althoughthis noise
cannotbe heard,it cangenerate intermodulationdistor-
tionanddamagethe
speakers.
@ rapeMoNtroR
swrrcHEs
Employfor tapeplayback or to monitor a recordingin
progress.
1: Playbackor monitoringof atapedeckconnected
to
theTAPE1
jacks.
2: Playback or monitoringof a tapedeckconnectedto
theTAPE
2iacks.
NOTE:
L Be sure to set the switches to the uppet (OFF) position
when playing rccords or listeninq to brcadcasts.
2. When lecording with two tape decks simultaneously, do not
opefate the tape monitor I switch as this will interupt the
signal to the TAPE 2 deck.
@ FUNCTIONSELECTOR
Depressthe function switchwhich correspondsto the
programsource.Turn the volume control down first
beforeselectinga different function switch while the
sound
tromone
program
sourceisbeingreproduced.
six-37clcl
@ enlnNce coNTRoL
Use
this control to balancethe volume
of the left and
right channels. First,
however,
setthe mode/FMmuting
switch
to MONO/OFF.
lf thesoundappearsto belouder
on theright,it means
thatthevolume
ot theright channel
ishigher. Turn the balancecontrolto the leftandadiust.
Conversely,if the soundappearsto be louder
ontheleJt,
it means that the volume
of the left channelishigher.
Therefore,
turn the balance
control to the right and
adjust. After adjusting.
return the mode/Fl\4
muting
switchto STEREO/ON.
@ MODE/FMMUTINGSWITCH
Thisswitchisacombinationof theFl\ilmuting
switchand
the mode selectswitch. When settingthis switch at
STEREO/ON
position
thereproductionis
jnstereo
mode,
whilethe Fl\il
mutingfunctionactsto suppressunpleasant
interstation
noisewhiletuningbetweenFMstations when
listening
to FM broadcasting.When
settingthisswitchat
MONO/OFF
position,
however,
reproductionisin mono
mode.while the FM mutingfunction
doesnot act,thus
enabling
suitablereceptionof weak radio
stations
when
tuninginto the FMbroadcasting
station.
NOTE:
Recoding stercophonically with the mode/FM muting swiach in
the MONO/OFF position may cause deteriorction in channel se-
@ LOUDNESS
SWITCH
Whenlistening
to a perlormance with the volume con-
trol turneddown,depress
thisswitchandthebass
will be
accentuated.
When
thevolume islow,thehuman ear
finds
it harderto
hear
thebassthanwhen
thevolumeishigh. Theloudness
switchisthusdesignedto compensate forthisdeliciency.
By depressing
this switch,the basscomethroughmuch
more
stronglyandthe sound takesona
punch
evenwhen
thevolumecontrolis
turneddown,
@ VOLUME
CONTROL
Usethiscontrol
to adjusttheoutputlevelto thespeakers
and headphones. Turn it clockwiseto increasethe out-
put level.Nosoundwill beheardif you set
it to "0."
Depressthis switch
for FM broadcasts.
Depressthis switch
for AM broadcasts.
Depressthisswitch whenlistening
to an
audio component connectedto the
AUX
jacks.
Oepressthis switch
whenplaying
a re-
cord on the turntableconnectedto the
PHONO
iacks.
NOTE:
Onlyonefunctionswitchshouldbedeptessedat a time.
5

3. BLOCK
RFBlock
AM STEREO
OUT
AFBlock
DIAGRAM
]NOICATORIUEE
c (NAt201)
SPEA(ERB
ll HEAo
t;
r
a i,BfffiJ*
G)
o
r$
t
REC F.AY R€C PLAY
R CHANNEL ( SAME AS L CHANNEL)

4. CIRCUIT
DESCRIPTIONS
4.1 FMTUNER
Front End
The FM front end of SX-3700 includes a 3
ganged tuning capacitor, a dual-gate MOS EFT-
equipped 1-stage RF amplifier, and a modified
Clapp circuit local oscillator. This oscillator is a
voltage controled oscillator employing a vari-cap
(variable capacitancediode). When the quartz-lock
system (refer to "Quartz-lock system") is not in
operation, a constant voltage is applied to the
diode.
lF AmplifierandDetector
Theseemploy 3 ICs and 3 dual-elementceramic
filters. The IC (HA1201) of the first 2 stagecon-
stitutes a single-stagedifferential amplifier current-
limiting limiter. The IC (PA3007-A) in the third
stage,
an improvement on the former IF systemIC
(PA3001-A), includes an IF limiter amplifier,
quadrature detector, meter drive, and other cir-
cuits. Performance in terms of distortion, S/N
ratio, delay characteristics, and other parameters,
shows a marked improvement in comparison to
the PA3001-A.
Multiplex Decoder
The recently developed multiplex decoder IC
(PA4006-A) combines MPX decoding lvith muting
functions in a single IC, thereby handling the
functions of the more conventional MPX IC
(PA1001-A) and AF MUTING IC (PA1002-A).
Distortion ratings and S/N ratio have been
further improved by incorporating a chopper type
MPX decoder. The chopper type switching circuit
(see Fig. 4-1) operates by switching the signal
either to ground or to the through circuit, thereby
eliminating the generation of unwanted nois€ or
distorition. Furthermore, sincethe PA4006-A fea-
tures DC direct{oupled switching with the detec-
six-37ClC'
tor, there isno deterioration in separation
at the
low frequency end.
Besides the decoder and muting circuits, the
PA4006-A also incorporatesthe pilot signalcancel-
ler, stereo auto selector, VCO killer circuit, MUT
amolifier. and MUT control ctcuit.
Composite
signal
4l1i\r1l''
-)A
,)
-\-A
t
InoutffiOutOut
JlIlIl[JlIUUrn^---a i
s*iiit''i'iri
-ri:-'',
ir
"--\y' - 7
,,T
Fig.
4-1 Choppertypeswitchingcircuit
Ouartz-Lock System
The quartzJock system featured in the SX-3700
stereo receiver is a frequency servocontrol system
employing a crystal resonator. Any displacement
in the intermediate frequency (IF) is detectedasa
DC voltage by the discriminator (equipped with a
crystal resonator), resulting in the local oscillator
frequency being conected and subs€quently
locked. This extremely stable frequency servo-
control system thus ensures
that tuned frequencies
remain tuned securelyfor as
long asrequired'
When the IF signal appears
at pin no.17 of the
IF system IC (PA3007-A), it is amplified and
applied to crystal detector (seeFig.4-2) which
consists of diodes connected in parallel in a series
resonance clcuit equipped with a crystal resona-
tor. The resonance
frequency isthe same
asthe IF
frequency (10.7MH2), which meansthe impedance
at this time will be minimal, resulting in the output
beingreducedto a minimum level. If the input fre-
quency increases, the reactance of the canacitance
CRYSTAL
DETECTOR
-"----f::,
| '''i'ill
| +:
t: (!r t5 r: I I I
;i..*'F--?-'i+r
I
ITNATOR= rll'
t_-----F-- I | ;
l_ ,t ?-J

stage (C) is reduced, and the reactanceof the in-
ductance stage (L) increased, resulting in AM
detection by D2 which leavesthe positive portion
of the IF signal. If the input frequency decreases,
L stagereactance is decreased
and C stagereact-
ance increased, resulting in AM detection by D1
which leaves
the negativeportion of the IF signal.
The L stage and C stage reactances increase as
the degreeof detuning in the respectivedirections
is increased,resulting in a subs€quent increase in
the detector output. By thus attaining S-cuwe
characteristics, FM detection becomes possible.
Since the IF signal is an FM signal frequency
deviation due to modulation it will be symmetrical
about a central axis. And if the central frequency
is equal to the resonancefrequency, the detector
output DC level will be zero. If, however, there is
any displacement in the central frequency, fre-
quency deviation in respect to the detector will
become asymmetrical, resulting in the generation
of a DC voltage. This DC voltage is passed
through
LPF1 (IF filter) and LPF2 (AC filter) to form a
correction voltage which is applied to the variable
capacitance diode in the local oscillator, thereby
correcting the oscillator frequency to obtain a
constant IF (i.e. a constant tuned frequency).
Since the central frequency of the crystal det€c-
tor is regulated by the crystal resonator, tuned fre-
quencies of extremely high stability are obtained.
r Limiting the t ocking Range
If the quartzJock range is too wide, it will
overlap with strong adjacent broadcastingfrequen-
cies and result in considerable tuning difficulties.
A DC amplifier is therefore used as a limiter
(limiter action by NFB circuit zenerdiodes)which
restricts the voltage applied to the variable capaci
tancediode, thereby limiting the quartz-lock range.
A DC voltage appears at pin no.13 of the IF
system IC (PA3007-A) when the antenna input
level drops below SpV, or when the tuned fre-
quency has been detuned by more than 1 100kHz.
This DC voltage (FM muting signal) is applied to
the gate of Q2 (FET) via a Schmitt circuit, result-
ing in the FET being turned on, and the quartz-
lock circuit beingtumed off .
4.2 AMTUNER
The AM tuner stage
employsa 2-gangedtuning
capacitor,
a singleclement
ceramicfilter, an NPN
transistor RF amplifier, a PNP transistormixer
(converter),
andanNPNtransistor
IF amplifier.
4.3 DISPLAY
CIRCUIT
Frequency
Display
Frequencies
received
by the SX-3700are dis-
played in digital form by fluorescent indicator
tube (FL tube). Each digit employs up to 7 seg-
ments (a - g) (seeFig. 4-3) to display all numerals
from 0 to 9 (with the exception of the left hand
digit which employs only 2 segmentsb and c).
Lt
ti
d
Fig.4-37-segment
display
The signalsourceduring both AM and FM recep-
tion is the local oscillator. The signalis passed
via
a buffer amplifier (FET) to the prescalar IC
(M54451P) where it is subjectedto frequency divi-
sion (1/8 for AM and 1/80 for FM) before being
applied to the frequency counter IC (PD5009).
This IC is responsible for the dynamic drive of the
?-segment 5-digit display (each digit being tumed
on accordingto time-sharedsequentialscanning).
An outline of the composition of PD5009 is
given in block diagram form in Fig. 4-5. With the
FL tube a - g segments
(anode) for eachdigit con-
nected in parallel, the D1 - D5 time division pulse
signals (see Fig. 4-6) applied to each grid (inde-
pendent grid for each digit) result in the digits
being lit up in successionfrom the left hand side.
Each digit is lit up for 1ms during each 5ms inter-
osc,sr6NAL
OSC.SIGNAL
sr.NAL FL luB€
Fig.
4-4 Frequency
displayblock
diagram
val. Pin no.7 of PD5009 is the brightnessselector
terminal. The time division pulse width is set to
8009s for H level input signals,and to 2009s for
L level signals,thereby varying the degree of FL
tube brightness (by varying the segmentlighting
period). Note that since the power indicator FL
tube is driven by static drive, the degreeof bright-
nessmay bevaried by changingthe grid voltage.
The 5.12MHz crystal oscillator generates the
basic signal used in the preparation of the time
division pulse signal and the counter gate circuit
control signal.
r

l;
Terminals S1 - 54 (pin nos. 3 -6) are used in
designating reception mode. The 2 reception
modes employed in the SX-3700 (seeTable 1) are
designated by varying the combination of input
levels (H and L). The 3 different IFs during FM
mode are required in coping with IF offset in the
IF ceramic filter stage, S3 and 54 being preset
during FM mode according to the ceramic filter
characteristics .
Although the SX-3700 FM stage quartzJock
system is capable of locking any frequency within
the FM band, the 10kHz digit (digit in the second
decimal place) in the FM frequency display will
appearonly as5 or 0.
The frequency display FL tube alsoincorporates
the TUNING and SIGNAL indicators. And al-
though the segrnents(anode) for these indicators
are static driven by the corresponding drive cir-
cuits, the grid is driven according to the D3 time
division pr:lsetiming, thereby placing the segments
gC= H (ARIGHT,
sx-37c'cl
under dynamic drive. In addition, the AM and FM
indicators in the frequency display section are lit
according to the Db timing, while the kHz and
MHz indicators are lit according to the D1 timing.
MODE st s2 s3 s4 lF {MHz)
H H 10.73
HLH't0.70
HLHH'r0.67
LH L 450kHz
Table
1
TUNING Indicator
Circuit
The TUNING indicator consists of a center
tuning indicator (which lighLs up when a broad-
casting station frequency is properly tuned) and
2 detuning direction indicators which indicate the
direction in which the station hasbeentuned away
from. The corresponding drive circuits are out-
lined in Fig. 4-7.
The TUNING indicator is activated once the
station has been tuned to within t 100kHz of the
center frequency. This is because
Q22 istumed on
and Q21 tumed off (resulting in the detector dif-
ferential amplifier IQ19 & Q20l being tumed off
and Q14 being tumed on) by the FM muting
signal appearing at pin no.13 of the IF system IC
(PA3007-A) and passed via the Schmitt circuit
(Q15 & Q16) when the station is tuned away by
morethan t 100kHz.
t,
+1,.
PRESETABLE
5-OIGIT
OECIMALCOUNTER
22-BlT r 15 ROM
\ (^,
Fig.
4.6 D1.D5timedivision
pulse
signals

The DC voltageon pin no.4 of PA300?-A de-
scribesan S curve when tuning to and away from
a particular broadcasting frequency, the voltage on
pin no.2 serving as the reference level. This DC
voltage is amplified by the differential amplifier
(Q19 & Q20) and then applied to a poladty detec-
tors switch circuit (Q16 & Q26).
SCHMiTT
Fig.
4-7TUNINGindicator
driver
circuit
When tuning to a frequency from the high fre-
quency side (or tuning away from the frequency
to a higher frequency), the voltage on pin no.4 will
behigher than that on pin no.2. The Q20 collector
voltage will thus be lowered and the Q19 collector
voltage raised, resulting in Q26 being turned on,
and the higher frequency (right hand side) detun-
ing direction indicator alsobeing turned on. When,
on the other hand, the broadcasting frequency is
approached from the low frequency side (or when
tuning away to a lower frequency) the pin no.4
voltage will be lower, resulting in Q16 beingturned
on to light up the lower frequency (left hand side)
detuning direction indicator. When either Q16 or
Q26 is on, the Q14 base voltage will be high,
resulting in Q14 being turned on and Q18 turned
off, which means that the center tuning indicator
will not be lit up.
Once the broadcastingfrequency hasbeentuned
properly, the voltages on pin nos.2 & 4 will be
equal. Consequently, Q16 and Q26 will both be
turned off, which meansthat neither of the detun-
ing direction indicators will be on in this case. And
since Q14 is turned off becauseof the decreased
basevoltage, Q18 will be turned on, and the center
tuning indicator light up. Furthermore, C16 is
chargedup via R84, resulting in Q23 beingtumed
on, thereby lighting up the Quartz Locked indi-
cator LED.
SIGNAL Indicator
Circuit
The SX-3700 SIGNAL indicator consists of an
FL tube 5-point indicator display. Thesignal
meter
drive signal obtained from the FM IF system IC
(P43007-A) and AM tuner is first amplified and
then applied to the indicator drive IC (HA12010).
This IC contains 12 pairs of voltage comparators
similar to those employed in the power indicator
circuit, 5 of these pairs being used to drive the
SIGNAL indicator.
r
Fig.4-8SIGNALindicatordrivercircuit

F
fD
4.4 EOUALIZERAMPLIFIER
This circuit is an NFB type equalizer amplifier
with newly developed high performance IC
(M5214L-P).
This IC is a low-noise and low distortion type,
and provide an openloop gainof 105dB. The main
performance specifications for this circuit include
a voltage gain of 35.5dB (at lkHz), a phono
dynamic margin or maxirnum allowable input level
of 250mV (lkHz, O.O2Vo
THD), S/N ratio of
79dB (at 2.5mV input, IHF-A), and equalization
within t 0.2dB (2OHz - 2OkHz).
4.5 TONECONTROL
AMPLIFIER
This circuit is an NFB type tone control ampli-
fier with newly developed high performance IC
(M5214L-P).
4.6 POWER AMPLIFIER
This is the basic circuit arrangement of power
amplifier. The first stageis a differential amplifier
(Q3), the load circuit of which is a current mirror
employing an NPN twin transistor (Qb). The cur-
rent mirror provides push-pull operation in this
stage, v/hich serves to cancel even numbered
harmonics and further increase
gain.
The pre-driver stage(Q7) with a current mirror
circuit (D5, Q11), enables stable operation and
provides high voltagegain.
The power stage
isa Darlington connection pure
complementary SEPP ctcuit, and has an output
of 45W (8O load. at both channels driven, THD
O.O2%,2OHz-2OkHz\.
Eix-37c'Cl
4.7 POWERINDICATOR CIRCUIT
The SX-3700 output power indicators feature
fluorescent indicator tube (FL tube). In this tube,
thermionic emissions from the cathode are ac-
celerated into the fluorescent substance of the
segmentalanodes,
resulting in the emissionof light.
This tube is used to indicate numerals.letters, and
other symbols.
An outline of the FL tube drive circuit is shown
in Fig. 4-9. The output circuit signalisapplied to
pin no.6 (4) of the IC (TA7318P-A). The IC con-
tains a detector circuit, compressor (40dB)' and
peak hold circuit for both left and right channels.
The dynamic range of the signalisthus contracted
by 40dB to obtain a "peak held" DC voltage.
The output power indicator segments
of the FL
tube are driven by the HA12010 ICs (one for each
channel) equipped with 12 pairs of differential
amplifiers. These amplifiers are biasedat increas-
ing levels, so each amplifier will commence to
operateseparatelyasthe input level increases.And
since these amplifiers apply the voltage to the out"
put power indicator segments, each successive
segment will light up in tum as the input level
rises.
4.8 PROTECTIONCIRCUIT
In order to protect both the amplifier and the
speakers,the SX-3700 has been equipped with a
protection circuit which is opened and closed
automatically by a relay in the output circuit.
As can be seenfrom Fig. 4-11, this circuit consists
of 3 main component parts.
)c (fafatSP) t/2
OE
TECIOR
FLUORESCEN
I ]NDICAIOR TU
gE
T^
Fig.4-9 Powerindicatorcirclrit
ac 7.2v

The relay drive circuit controls relay operation,
delaying relay closure when the power is switched
on, opening the relay quickly when the power is
tumed off, and a.lsoopening the relay in response
to instructions from each detector circuit. When
the power is first switched on, C4 is charged up
via R8, thereby increasingthe potential difference
across
the capacitor terminals. Once this potential
difference exceedsthe zener diode, Q6 is turned
on due to the forward biasing, thereby closing
the relay contacts. When the power is switched
off, C4 is dischargedrapidly via Db and R7, result-
ing in Q6 being tumed off and the relay contacts
being opened.
The overload detector circuit outlined in Fig. 4-
10 below consistsof a Wheatstone bridge with the
load RL forming one of the arms. Q3 is biased
by the potential difference betyyeen
diametrically
opposite comers of the bridge circuit. If the RL
value drops below a certain fixed level, Q3 will
be tumed on due to forward biasing. The charge
on C4 in the relay drive circuit will thus be dis-
charged via D3 and Q3, resulting in Q6 being
tumed off and the relay contacts being opened.
F|€l€y driv€ circuit
Fig.4-10
Overload
Detector
Circuit
If for any reason a DC voltage is generated at
the output, it will be detected by the DC voltage
detector circuit, resulting in the relay contacts
being opened to thereby protect the speakers.
Rb and C2 form a low-pass
filter designedto block
normal signal components, thereby preventing the
application of signal voltages to the basesof Q4
and Q5. If a positive DC voltage appears at the
output, it is divided by R5 and R6, and applied
to Q4 and Q5. Since the baseof Q5 is connected
to ground, this transistor will remain off due to
the reverse bias applied. And since the emitter
of Q4 is connected to ground, this transistor will
be tumed on due to a forward bias. Consequent-
ly, the baseof Q6 is grounded by Q4, resulting in
Q6 being turned off and the relay contacts being
opened. If a negative DC voltage appears at the
output, Q4 is tumed off due to a reverse bias,
while Q5 is tumed on due to a forward bias. And
since a negative voltage is applied to the emitter of
Q5 in this situation, Q6 istumed off and the relay
contacts ooened.
,l
Pow€r
amplifi€r
""*";.;;;lOverload detector
circuit DC voltag€ dstsctor circuit
Fl[&'#bfr
ll
J
R6lay
driv€
circuit
Fig.
4-11Protection
Circuit
AC powor supply
I
J
|
;.+
t:. 4,

six-37ClCl
5. DISASSEMBLY
Bonnet Case
Remove the four screws O on eachsideof the
bonnet case.
Bottom Plate
Remove the eleven screws O to detach the
bottom plate.
Front Panel
Remove the all control knobs except push
knobs. Remove the two screws tp and two nuts
Q from the front panel.
?^
d
Fig.5-1Disassembly
-+--
\?
n
Bonnetcase
ottomplate
Front
panel

6. PARTS LOCATIONS
FrontPanel
Front panel
assembly
ANB-883
Pushknob
AAD-226
Front View with PanelRemoved
F
L assembly
AWV-o12
Switchassembly
GWS-233
Switch (POWER)
ASA-507
Phone
jack(PHONES)
AKN{30
Variable
resistor
(TON
E
)
ACT-127
Switch
ASK.157
The [, mark found on some component parts indicates
the importartce of the safety factor of the part. There'
fore, when replacing, be sure to use parts of identical
designation.
Knob
(TUNING)
AAA065
Bonnet
case
AMM€89
Leverknob assembly
AAD-139
Function switchassembly
AWS-149
Lead
out assembly
AWVOl1
,lt,€
Variable
resistor
25Ok
(VOLUME)
ACT-126
Switch
(LOUDNESS)
ASK.157
Switch
(MUTING)
ASK-l59
Variableresistor
1M (BALANCE)
ACT{21
F

tl^
v2
/';^
/g^
8^
D
J.'
Rear
Panel
Bar-antenna
assembly
ATB€24
Terminal
(AM
STEREO
OUT)
AKB{)76
Terminal (ANTENN
AKAOl4
Pin
iack
AKB{63
Top View
Power amp/protector assembly
GWM.159
IPower transformer
ATT696
sx-37clcl
I ACsoctet
(Ac OUTLETS]
AKP{39
I AC power cord
ADG{23
Terminal
(SPEAKER)
AKEO44
Tuner/AF assembly
GWM.160
Detector assembly
GWX463
15
n^

7.
DIAL CORDSTRINGING
1. Remove the bonnet case and front panel as
described in the "Disassembly" section on
page1
2. Remove the tuning drum from the shaft of the
tuning capacitor.
3. Tie one end of the cord to the stud Q located
insidethe tuning drum.
4. Rotate the tuning capacitor right around until
the rotor bladesarefully intermeshed.
5. Secure the tuning drum back onto the tuning
capacitor shaft, making sure that the securing
screw I faces
directly upward.
6. Pass
the cord out through the small opening in
the circumference of the tuning drum (see
diagram), and then take it over pulleys A, B,
and C in that seouence.
\
7. Wind the cord around the dial shaft 3 times.
8. Pass it over pulley D, wind it around the tun-
ing drum 2 times, and finally tie it to the
springhook O sothat it istensioned.
9. T\rm the dial shaft, and check that the cord
movessmoothly.
10. Cut off any excesscord.
11. Tum the dial shaft counter-clockwise as far
asit will go.
12. Align the dial pointer with the starting point
of the dial scale,
and then pass the cord overit.
13. Check that the dial pointer is in line with the
starting point of the dial scale.
14. Finally apply the locking paint to the cord
securing positions (stud O and spring hook
O ) and the dial pointer connection.
D
ialshaft
Tuning
drum
Starting
point
Dial
pointer Dial
pointer
Fig.
7-1 Djal cordstringing

Y
8.ADJUSTMENTS
8.1 FM
TUNER
. Connect the FM SG (FM signal generator) to
the FM antenna 300O terminal.
. Set the FUNCTION switch to FM. Set the FM
MUTING switchto MONO.
o The tuning coils in the FM front end doesnot
have an adjusting core. Consequently, track-
ing adjustments at 90MHz are performed by
regulating the gap between rotor and stator
of the tuning capacitors (VC-1, VC-2, and
VC-3). The expression"adjust VC (VC-1,
VC-2, and VC-3) found in the text means
that the two outer rotor blades of each of
these tuning capacitors are to be extended
outwards with spatula (Part No. GGK-066)
asshownin Fig. 8-1.
Stator
1. Set the SX-3700's dial pointer to 106MHz,
and the FM SG output to 106MHz, 106dB
(modulation -40OHz, t7 SkHzdeviation).
2. Adjust the TC3 to obtain a maximum output
level
(RECterminal).
3. Then tune the dial pointer to 90MHz, and set
the FM SGoutput frequency to 90MHz.
4. Adjust the VC-3 to obtain a maximum out-
put level (RECterminal).
5.Repeatsteps1to 4 above.
6. Reset
the FM SG output levelto 20 - 30d8,
and adjust TC7, TC2, and TB at 106MHz, and
VC-1 and YC-Z at 90MHz in the same man-
ner asdescribedabove in steps1 to 5.
These adjustments will ensure optimum sensi
tivity in the 90MHz to 106MHz range, and
minimum difference in sensitivity between the
two extreme frequencies.
7.Set the FM SG output to 98MHz, 66dB, and
tune the SX-3700 to this frequency.
8. Adjust the core of T2 to reduce distorition in
the output (REC terminal) to a minimum.
9.Adjust the VR3 so that the 5-point SIGNAL
indicator reads 5 at 55dB of FM SG output.
To REC
terminal
Botor blade
Spatula
{GGK
066)
Stator
-
Rotor
blade
ql+
4fllnx
X
ffi
X
Fig.8-l Adjustmentof tuningcapacitor
F
Jb
JI
ptn
VC
IN
(EXT.
MOD)
tr^ Fiq.
8-2 Adiustment
point

Multiplex Decorder
* Connect the MPX SG (FM multiplex generator)
to the external modulator terminals of FM SG,
thereby using FM SG as extemal modulation.
1.
Set the FM SG output frequency to 98MHz,
output level to 60dB (unmodulated), and tune
theSX-3700
to thisfrequency.
2. Adjust the VR1 to obtain a 76kHz signal at
No. 7 terminal (AWV-011, 36 Pin) on the tuner
assembly.
3. Set the MPX SG modulation output to pilot
signal
(19kHz) only, and set the FM deviation
of 7.5kHz(107o
modulation).
4. Adjust the VR2 to obtain minimum leakage
of the 19kHz pilot signal
at the REC terminal.
5. Raise the FM SG output level to 80dB, and
set the MPX SG to Main lkHz (L+R), 67JckHz
deviation (907o modulation), and pilot signal
to 7.5kHzdeviation
(10%modulation).
6. Adjust the T1 core to within 190" to obtain
minimum distortion in the demodulated output
(RECterminal).
sx-37C'C'
8.2AM TUNER
. Connect the AM SG (AM signal generator)
to the AM antenna terminal via a 1kO resistor.
o Setthe FUNCTION switch to AM.
1. Tune the SX-3700's dial pointer to 600kHz,
and the AM SG output to 600kHz, 100dB
(modulation
-40OHz, 3O%
).
2.Adjust the core of T101 to obtain maximun
output level (REC terminal).
3.Then tune to 1400kH2, and set the AM SG
output frequency to 1400kHz also.
4. This time adjust TC5 to obtain maximum
output level (REC terminal).
5. Repeatsteps1 to 4 above.
6. Set the AM SG output level to 30dB, adjust
the antenna coil along the bar-antenna and
TC4 andTC5 at 1400kHz in the samemanner
as described in the above steps. This is the
adjustment for optimum sensitivity across
the frequency band, and minimum difference
in sensitivity
at differentfrequencies.
ACvoltmeter
antenna
coil
To REC terminal
Fig.
8-3 Adjustment
point
Oscilloscope
AM signal generator

8.3 IDLE CURRENT
ADJUSTMENT
1.Turn the VOLUME control down to minimum
level, turn the power on, and wait about 10
minutes.
2. Connect a DC voltmeter to the TP terminals
(L ch; TP48 + and 49 Pin R ch;TP47 +
andTP46 ) of the GWM-159.
3. Check that the voltage between 49 Pin and
TP48 (L ch) lieswithin the DC 2.2mV-100mV
range. Then make a similar check for the R ch
between "1P47 and TP46. If the voltage is less
than 2.2mY, cut jumper A (L ch),
and
jumper B
(R ch). If thevoltageexceeds
100mV, checkfor
circuit failure.
8.4 FL INDICATOR
CIRCUIT
Frequency
Display
Circuit
The offset switching circuit is employed in
PD5009 AM/FM band selection and FM IF offset.
If cuts aremadeas
directed in the table 2, the level
of each pin in PD5009 will be switched to the
mode indicated in Table 1 on page
g.
FM c€ramic
filt€r 011 412
R121okO
O
p€n
Blue The jumper betweencollector
and
emitter is
to be left open. R1210kn
Open
Orange Th€ jumper betweencollectorand
emitter is
to be left open.
Table
2
s)<-37clCl
. If the SX-3700 frequency display reads
97.95MH2 or 98.05MH2 when a 98.00MH2
signal is applied to the receiver, adjust TC1 so
that the display reads98.00MH2 correctly.
. If an accurate 98.00MH2 input signalsourceis
not available, tune the receive to the nearest
known broadcasting station in the 98MHz re-
gion, and check that the station's frequency is
correctly displayed, adjusting TC1 if necessary.
Output PowerIndicator
Calibration
1.
Apply a lkHz signal to the AUX terminals.
2. Adjust the level of this input signal so that the
voltage on the output terminals (SPEAKERS)
read
8.95V (AC).
3.Adjust VR1(L) and VR2(R) so that the out-
put power indicator read 10 watts.
vR2R
ip47
Fig.
8-4 Adjusrment point

g.SCHEMATICilAGRAMS,P.C.BOARDCONNECTION
DIAGRAM AND PARTS LIST
External
Appearance
of Transistors
andlCs
2sA733A
a.) ..,.. ?33Ii3-,-m ,,""".
2SC945A rvp.
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2SA949 rvo.
No
2SC1885
25C2229
2SA7265 2S8507
25C2291
25K61
3SK73 rype
t\45214L-P
PA3007-A
PA4006-A
TA7318-A
PD5009
/
2SA913
2SB
834
2SD313 rYPe
2SD8364
2SD880
2SC1913
2SC461
2SC535
2sc1384
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+ lfJ rve€N6
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25C2525
NJM4558DV
HA1201
pPC4558C ,ni44
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