Pioneer SX-3900 User manual

$eftice nual
FM €Iuartz Locked
STEREORECEIVER
six-3s|oo
()proNEER'

MODELSX.3gOO
COMES
IN
TWO
VERSIONS
DISTINGUISHED
AS
FOLLOWS:
Type Voltage Remarks
KU 120V
only U.S.A.
model
5/U I10V,
120V,
22Oand
240V (Switchable) U.S.
Military
model
This service
manual
isapplicable
to the KU type. When
repairing
theS/G
type,please
see
the
additional
service
manual
(see
pages
47-56l..
CONTENTS 1.
SPECIFICATIONS
1.
spECtFtcATtoNS 2 PowerAmplifierSection
2'
FRoNr
PANEL
FACILTTIES a Continuous
Power
0utput
0f
120
wattsxper
chan-
3'
BLocKDIAGRAM 7 nel,min.,
at
8ohms
from20Hertzto 20,000
4.clRCUlr
DESCRIPTIoNS Hertz
withn0m.rethan0.005%tolal
harmo-
4.1 FMTuner Section 8 niC
diStOftiOn.
4.2 AMTunerSection 9 To,rl
Harmonic
Distortion
(20
Hertz
to20,000
Hertz,
4.3 Audio Section 9 g ohms)
4.4 DisplayCircuits ....... 11 continuousratedpoweroutput..
Nomorethan0.005%
4.5 ProtectionCircuit 13 60watts
per
channel
power
4'6 Surge
currentsuppressor " " " ' l5 ,",1r',jlltr,r.ionoirioriion
iuo
rrrrrltrl;f ;::ltjT:"fl
1E
5' DISASSEMBLY
' ' 15 continuous
rated
power
output
. . Nomorethan 0.005%
6. PARTSLOCATION 16 60
watts
per
channel
power
7. DIAL
CORDSTRINGING
. 18 output ' . . . ' Nomorethan0.005%
g. ADJUSTMENTS Frequency
Response
8.1 AudioSection 1e rnpr.s.nriiiui,vli,.np.oun..t,i;ff
T iorTln?,t'.2
*! aa
8.2 TunerSection. 20 . . . . . 'l
V/50
kilohms
9, SCHEMATIC
DIAGRAM 24 OUtPUt
10.
p.c.
BoARDS
coNNECTToN
DTAGRAM 29 -speaker ' ' ' ' ' A'B'A+B
Damping
Factor
(20
Hertz
to20,000
Hertz,8ohms)
I1.PARTSLIST. 35 ...60
12.
EXpLoDED
vtEW 41 Hr..;; rtr.ir.
iiHi, rrrortcircuiteo,
A network)
13.
PACK|NG.... 46 ""' 115d8
ADDTTTONAL
SERVTCE
MANUAL
FOR
S/G
TYPE 41 Preamplifier Section
I
nput
(Sensitivity/lmpedance)
PHONO
1,2.
. . 2.5mV/50
kilohms
AUX,TAPE
PLAY
1,
2,
ADAPTORIN
... ... 150mV/50kilohms
Phono
Overload
Level
(T.H.D.
0.005%,
1,000
Hertz)
PHONO
1.2... 300mV
OutPut
(
Level/l
mPedance)
TAPE
REC1,
2.
ADAPTOR
OUT 150mV
PREAMP
OUT
(RL:
50
kilohms)
. . . . 1Vl1
kilohms
(Volume:
max.)
TotalHarmonic
Distortion
(20
Hertzto 20.000
Hertz)
PHONO
1.2
(REC
OUT). . . . . . Nomorethan0.005%
(10V
output)

sx-3900
AUX,TAPE
PLAY
1,
2.
ADAPTOR
IN
No more
than
0.005%
(10V
output)
FrequencyResponse
PHONO
(R
IAA
Equalization)
. . . 20Hertz
to 20,000Hertz
t0.2dB
AUX,TAPE
PLAY
1,2,ADAPTOROUT
Ton.
contror ' ' ' ' ' 7Hertzto80000
Hertz
+9
dB
BASS. !4dB/!7dB(100H2)
f
u
rnover
F
requency
:2OOHz/400H2
TREBLE +gdB/t7dB
(10kHz)
TurnoverFrequencv
: 2kHzI
4k{z
Filter
LOW.. 15Hz
(-6dB/oct.)
HIGH
. 8kHz
(-6dB/oct.)
LoudnessContour
(Volume
controlset
at
-40dB
position)
. . . . +6dB
(100H2),
+3dB
(10
000H2)
HumandNoise
(lH
F,
short-circuited,
A network)
PHONO ... ... 86dB
AUX,TAPE
PLAY
1,2,
AM Tuner
Section
Sensitivity
(lH
F,Ferrite
antenna)
. .
(lHF,
Ext.
antenna)
" .
Selectivity
Signal-to-Noise
Ratio
lmage
Response
Ratio
lF ResponseRatio.
.
Antenna
Audio Section
Output
(
Level/l
mpedance)
FM
(100%
Mod.).
AM
(30%
Mod.) .
Semiconductors
lCs...
FETs.
Transistors
Diodes
M
iscellaneous
Power
Requirements
Power
Consumption
Dimensions
Weight
(withoutpackage)
FurnishedParts
Operatinginstructions
FM T-type
antenna
300sV/m
1
SpV
30dB
50d
B
40dB
40dB
Ferrite
loopstick
antenna
ADAPTORIN...
Attenuator.
FM Tuner Section
Usable
Sensitivity
(lH
F
)
50dBOuieting
Sensitivity
MONO
STEREO
Signal-to-Noise
Ratio
MONO
STER
EO
Distortion
(at
65dBf
)
MONO 100H2.
lkHz .
6kHz'
STEREO100H2.
ikHz .
105dB
-20d8
9.8dBf
(1.7pV)
14.2dBf
(2.8pV)
36dBf
(34.7pV)
83dB
(at
65dBf)
78dB
(at
80dBf)
0.1o/o
o.o7%
oJ%
O.27o
o.15%
O.2To
650mV/2.4
kilohms
20OmV
/2.4
kilohms
t5
o
89
62
AC
120V.60H2
350W
(UL)
526(W)
x 176(H)x
452(D)
mm
20-11/16(wl
x6-15/16
(H)
x 17-14/16(Dlin
2Okg
(441b2ozl
1
1
* Measured pursuant to the Federal Trade Commission's Trade
Regulation rule on Power Output Claims for Amplifiers.
NOTE:
Specifications and the design subject to possible modifications
without notice due to improvements.
6kHz
CaptureRatio.. 1.0d8
AlternateChannel
Selectivity
400kHz ......80dB
StereoSeparation
1kHz. ......50d8
3OHzto15kllz. ...... 35dB
FrequencyResponse ....2OHzto15kHz1!jaa
SpuriousResponseRatio
.. . . . . . 100dB
lmageResponseRatio ... 90dB
lFResponseRatio.. .... 100d8
AMSuppressionRatio ... 60dB
SubcarrierProduct
Ratio . . . . . . . 64dB
SCARejectionRatio .... 64dB
MutingThreshold 19.2dBf
(SgV)
AntennaInput . 300 ohmsbalanced,
75ohmsunbalanced.

2.FRONT
PANEL
FACILITIES
O POWER
SWITCH
SetthisswitchtooNtosupp|ypowertothereceiver.
There
will be
a short
delay
when
it isset
to ON'
because
the muting
circuit has
been
actuated
to suppress
the
unpleasant
noise
that issometimes
generated
when
the
Power
isswitched
on
and
off
'
@ BASS
TURNOVER
SWITCH
Use this switch to change
over the frequency in which
the sound adlustmentwith the bass
control is starting
to take effect. Select 200H2 or 400H2 in accordance
withthecharacterlstics'ofyourIisteningroomandof
your
speakers,
and
with your general
preference'
@ EASS
AND
TREBLE
CONTROLS
Use these controls to adiust the bass
and the treble'
lf you set the tone switch to ON and turn the bass
controItotherightfromitscenterposition,youwi||be
ab|etoemphasizethesoundinafrequencyrangewhich
is lower than that selected
by the bass
turnover switch'
Conversely,
turning
this
control
from the
center
position
to the left will attenuate
the sound'
You can use
the treble control to adjust
the sound in a
frequency
higher
than that selected
by the treble
turn-
over switch.
@ TONE
SWITCH
Set this switch to ON when adjusting
the bass
and
treble
controls.
When
set
to theOFF position'the
tone
control
circuitsaredisengagedandfrequencyresponseisf|at.
Thisfunctionisconvenientforcheckingphonocartridge
and speaker
tone quality and listening
room acoustics'
O TREBLE
TURNOVER
SWITCH
Usethis switch to change
over the frequency in which
the soundadjustment
with the treblecontrol is starting
to take effect' Select 2k{z or 4kHz in accordance
withthecharacteristicsofyourIisteningroomandof
your speakers,
and
with your general
preference'
@ noRProR
swlrcH
SetthisswitchtooNwhenreproducingsoundfroman
optional
component
which isconnected
to theADAP-
TOR
iacks.
Always
set
it
tothe
upper
position
ifyou
are
not
using
a
component
with
these
terminals'
@ TAPE
DUPLICATE
SWITCH
Set this switch to ON when you want to duplicate or
edit a pre-recorded
tape using two tape decks'
@ TAPE
MONITOR
SWITCH
Employ for tape
playback
or to monitor a recording
in
progress.
1: Playback
or monitoring
of a tape
deckcon-
nected
to the TAPE 1jacks'
SOURCE: Be sure to set to this position when not
using
the tape
deck
for playback
and moni-
tori
ng'
2: Playback
or monitoring
of a tape
deck
con-
nected
to theTAPE 2 jacks'
NOTE:
When listening
to records
or broadcasts'
be sure
to setthis
switch
to SOURCE'
Sound
wittnotbe
obtained
from
speakers
if it is set
to 1or 2.

€) BALANCECONTROL
Use
this control to balance
the volumeof the left and
right channels.
First,
however,
setthe mode switchto
MONO. lf thesound
appearsto belouder
on theright,
it
meansthat the volume
of the right channelis higher.
Turn the balancecontrol to the left and adjust.
Con-
versely,
if the sound
appears
to be louder
on the left, it
meansthat the volume of the left channelis higher.
Therefore.
turn the balance
control to the right and
ad
just. After adjusting,return the mode switch to
STEREO.
@ MODE
SWTTCH
Use this switch for selectingmono or stereo
perform-
ances.
STEREO: Set to this position for normal
operations.
MONO: When setto this position,
the left and right
channel signalswill be mixed and repro-
duced monophonicallyfrom both speaker
systems.
o voLUMECONTROL
Use this control to adjust the output level to the
speakersand headphones.Turn it clockwlseto increase
the output level.No soundwill be heardif you setit to
-. The scale is graduated
in dB which indicate
the
attenuationwhen
themaximum
output level is0dB.
€) MUTING
SWITCH
Set this switch to the *20d8 position to attenuate
the
audio
output indicatedby the volume
control
by 20dB.
Thereisno needto adjust
thevolume
control
if you use
this switch when turning down the audio output tem-
porarily
andwhen
changing
overrecords
or tapes.
G) HEADPHONE
JACK
Plug
the headphones
into this jack when you want to
listen
through
your stereo
headphones.
Releaseboth speaker
switches
if you want to listen
to
thesound
through
your headphones
only.
(E SPEAKERSWITCHES
Depressthe switch corresponding
to the speakers
con-
nected
to the SPEAKERS
terminals
(A or B)ontherear
panel.
You can depress
both of these buttons to listento the
sound from two pairs of speakersystems
at the same
time.
six-39cl(f
@ LOWFILTER
SWITCH
(15H2)
Depressthis switch in the eventthat turntablerumble,
recording
cutting noiseor other low frequency noise
becomesobjectionable.Attenuation in the frequency
band
below
15Hzis6dB/octave.
G) HIGHFILTER
SWITCH
(8kHz)
Depress
this
switch
if record
scratchnoiseor otherhigh
frequency
noise
becomesobjectionable.Attenuationin
the
frequency
band
above
SkHz
is
6dB/octave.
€) POWER
METER
This meter allowsyou to readout the rated
power level
on the fluorescent
display
tube when speakers
with a
nominal impedance
of 8 ohms are connected
to the
speaker
terminals.
@ DrAL
POTNTER
This
pointer
indicates
thebroadcasting
stations.
@ rnn
STEREo
rNDrcAToR
Thisindicatorlightsup whenreceiving
an FM stereo
program
if
the
FM
mutingoff
switch
isreleased.
@ oUARTZ
LOCKED
|ND|CATOR
This indicatorlightsup afterthe optimum tuning point
hasbeenobtainedanddisplays
thatthereceivingstateis
stabilized
by thebuilt-in
quartz
lock
circuit.
€D
SIGNAL
INDICATOR
This indicatorlightsin sequence
from leftthrough
right
during
the tuningof an AM or FM broadcast in
accord-
ance with the strengthof the signals being received.
The optimum tuning point is where the maximum
numberof indicators
light.
@rururNG
rNDrcAToR
When tuning in an FM station,the optimum reception
point is indicated
when the center
indicatorlights
up.
When the left indicatorhas
comeon, rotate the tuning
knob slightlyclockwise.Whenthe rightindicatorcomes
on,
rotatethe knob
slightly
counter-clockwise.
@ FREOUENCY
DISPLAY
Thisindicatesthe
frequency
whichistuned.
With FM reception,
the letters
"FM" appearon the left
of the displayand "MHz" on the right.WithAM recep-
tion, "AM" appearson the left and "kHz" on the right.
These change
when the function selector
position is
changed.
@ TUNINGKNOB
Usethis
knob
to tune in to broadcasting stations.
5

@ FM
MUTING
OFF
SWITCH
When
this switch
is
released
and
anFM broadcast
tuned
in, the muting
circuit
isactivated
inside
to suppress
the
annoying interstation noise between the broadcasting
frequencies
for noise-free
reception'
When
the
broadcast-
ing station
is far away or when receiving
a station
in a
fringe
area,
set
tne switch
to the
OFF position
and
then
tune in. lf there is a broadcasting
stationwith a strong
signallevelon the air next to a station whoseprogram
you want to receive,
you may not be able to tune in
satisfactorily
because
the sound will be drowned out
by the stronger
signals'
In cases
like this' setthe FM
MUTING OFF switch
to OFF (depressed
position)and
tune in. The muting circuit does not work when the
tuner is receiving
AM broadcasts'
lf tuning has been
performed
after
the FM MUTING OFF switch
has
been
depressedand a station selected.the quartz locked
circuit is set to the OF
F mode and the LOCKED
indicator
does
not light.
@ FM
25PS
SWITCH
Depress
this switch when listening
to a Dolby* FM
broadcast; otherwise keep this switch at the released
position.
@)
BRIGHTNESS
SELECTOR
Use this switch to select the brightness
of the power
meter
and
the
frequencY
disPlaY'
BRIGHT: When
using
the receiver
in daylight
or other
@ FUNCTION
SELECTOR
Deoress
the function switch which corresponds
to the
program source.
Turn the volume control down first
before selecting
a different function switch while the
sound
from one
program
source
is
being
reproduced'
FM:
AM: Depress
this
switch
for FMbroadcasts'
Deoress
this
switch
forAM broadcasts
AUX: Depress
this switch when listening
to an
audio component connected to the AUX
iacks.
PHONO
2: Depress
this
switch
when
playinga record
on
the turntable connected
to the PHONO 2
jac
k
s.
PHONO
1: Depress
this
switch
when
playing
arecord
on
the turntable connected
to the PHONO 1
i
acks.
NOTE:
OnlY
onefunctionswitchshould
bedepressed
at a ilme'
@ LOUDNESS
SWlrcH
When listening
to a performance
with the volume
control turned down, depress
this switch and the bass
and
treble
will be
accentuated'
When
thevolume
is
low,
thehuman
ear
f
inds
it harder
to
hear
the bass
and
treble
than
when the volume
ishigh'
The loudness
switch isthus designed
to compensate
for
this def
iciency.
By depressing
this switch'
the bass
and
treble
come
through
much more
strongly
and
the
sound
takes on a puncn even when the volume control is
turned
down.
bright
locations'
DIM: At night
or in dark
locations
when
the
exist-
ing
brightness
istoo high'
*Theword,,Dolby''isatrademarkofDoIbyLaboratoriesInc.

3.
BLOCK
DIAGRAM
TunerSection
sx-39clcl
OUARIZ LOCKEO
AM TUNER
AMO
Audio
Section
IAPE 1_-. ^ .":- ADAPrcR
RECPLAY OUT IN
R CnANNE- . IHL SAME A5 IHF L CHAN\EL )
FREA!ENCY
ar lr
'UIER
SECTION
FL TUSE
rc(
HAl2010
)
5-POINT SIGNAL
INDICATOR
ORIVE
rUN]NG INDICATOR FREOUINCY OISPLAY
FM MHz
,ODDD
, t_, t_t.t_t t_t
AM KHT
CoUNTER Oi
- D5
TIME DIVISION
7- SE6M€NT OECOD€R
ROM s1s2s3s4

4. CIRCUIT
DESCRIPTIONS
4.1 FM
TUNER
SECTION
Front
End
The FM front end of SX-3900 includesa 4
ganged tuning capacitor, a dual-gateMOS FET-
Eo"Too"A l-slage RF amplifier' and a modified
ai;; circuit llcal oscillator' This oscillator is a
uoiiug" controled oscillatoremploying a vari-cap
(varia'ble
capacitance
diode)'When
the.quartz-lock
,yrt"..t (refer to "Quartz-locksystem")is not in
operution, a constant voltage is applied to the
diode.
lF Amplifier
and
Detector
These
employ 3 ICsand 3 dual-element
ceramic
filters. fne lC (HA1201) of the first 2 stage
con-
stitutes a single-stage
differential amplifiercurrent-
ii-lti.rg limitet. The IC (PA300?-A)-in the third
stage,
an improvement on the former iF system
IC
liigool ai, includes an iF iimiter amplifier'
quadraturedetector, meter drive' and other cir-
cuits. Performancein terms of distortion' S/N
ratio, delaycharacteristics,
and other parameters'
,ho*, a marked improvementin comparison
to
the
PA3001-A.
Ouartz-Lock
SYstem
The quartz-lock
system
featured
in the SX-3900
stereo
receiver
is a frequency serl/o
control system
employing a crystal resonator' Any displacement
i.r itt"-lntlrmediate frequency (IF) is detected
as
a
DC voltage
by the discriminator
(equipped
with a
crystalresonator)'
resulting
in the localoscillator
ir"qt"r-r"y being corrected and subsequently
locked.
This extremely
stable
frequency
servo
con-
trol system thus ensures
that tuned frequencies
remain
tuned
securely
for as
longas
required'
When the IF signal
appears
at pin no'17 of the
IF system
IC (PA300?-A),
it is amplified
andap-
ptiei to acrystal
detector
(see
Fig' 4-1)
whichcon-
sists of diodes connected
in parallelin a series
resonance
circuit equipped
with a crystalresona-
i.r. irt" resonance
frequency
is thesame
asthe IF
fr"qr".r"y (10'?MHz),whichmeans
theimpedance
at it ls time will be minimal, resultingin the out-
fut being
reduced
to aminimum level'
If theinput
iruq.r"rr"y increases-
the reactance
of the capaci-
tanie stage
(C)is
reduced,
and
thereactance
of the
ir"rar"tun"u
stage(L) increased,
resultingin AM
Jetection by D2 which leaves
the positive
portion
of the IF signal.
If the input frequency
decreases'
L stage
reactance
is decreased
and C stage
reac-
tanceincreased,
resulting
in AM detection
by D1
which leaves
the negative
portion of the IF signal'
it'r" t stage
and C stage
reactances
inctease
asthe
degree
oidetuning in the respective
directions
is
in&eased,resulting in a subsequent
increase
in
the detector output. By thus attaining S-curve
characteristics,
FM detection becomes
possible'
Sincethe IF signal
isan FM signal
frequencydevia-
tiorl-a"" to iodulation, it will be symmetrical
about acentralaxis.
And if the central
frequency is
equal
to the resonance
frequency,
the detector out-
o,rt OC levelwill be zero.If, however,
thereis any
displacementin the central frequency, frequency
deviationin respect
to the detector
will become
aryrrr-utri"a1, resulting in the generation
of a DC
"liiug". This DC voitage is passed
through LPF1
(IF filter) and LPF2 (AC filter) to form a correc-
iion voltagewhich is applied
to the variable
capaci-
tancediodeinthelocaloscillator,therebycorrect-
ing the oscillator
frequency
to obtain a constant
tn'
(i.e.
aconstant
tuned
frequency)'
Since
the central
frequency
of thecrystal
detec-
tor is regulated
by the crystal resonator'tuned
frequencies of exiremely high stability are ob-
tained.
lc (
PA5007-A )
FM FRONT
END
CRYSTAL DETECTOR
| ----, I
:(L) 13 +i
CIRCU
IT
Fig.
4-1 Ouartz
Lock
SYstem
a

o Limiting the Locking Range
If the quartzJock range is too wide, it will
overlap with strong adjacent broadcasting fre-
quencies and result in considerable tuning diffi-
culties. A DC amplifier is therefore used as a
limiter (limiter action by NFB circuit zenerdiodes)
which restricts the voltage applied to the variable
capacitancediode, 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
ievel drops below 5pV, or when the tuned fre-
quency has been detuned by more than t100kHz.
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-
Iock circuit being turned off.
Multiplex Decoder
The recently developed multiplex decoder IC
(PA4006-A) combines MPX decoding with 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. 4-2) operates by switching the signal
either to ground or to the through circuit, thereby
eliminating the generation of unwanted noise or
distortion. Furthermore, since the PA4006--4 fea-
tures DC direct-coupled switching with the detec-
tor, there is no deterioration in separation at the
Iow frequency end.
Besides the decoder and muting circuits, the
PA4006-.4 also incorporates the pilot signalcancel-
ler, stereo auto selector, VCO killer circuit, MU'l
amplifier. and MUT control circuit.
Composite
signal
Inprt Output
JUIIUUUIJUIJU'
.}. I
switchins
,in"r'r
S/ --'I
nL
Fig.4-2 ChopperTypeSwitchingCircuit
4.2AMTUNER
SECTION
The AM tuner section consists of a 2-ganged
tuning capacitor plus an IC (HA1197) which con-
tains a 1-stageRF amplifier, converter, 2-stage
IF
amplifier, detector, and AGC circuit.
The AM STEREO OUT terminal on the rear
panel is for connecting to an AM stereo broadcast
decoder adaptor. The signal appearing at this ter-
minal is the converter output passed via a buffer
(emitter-follower) stage.
sx-39clo
4.3AUDIO
SECTION
PhonoEqualizer
Amplif
ier
Fig. 4-3 shows the basic configuration of the
circuit. An S-N ratio of 86dB (at 2.5mV input,
IHF-A) has been achieved by using a ultra-low-
noise PNP transistor (2SA978) at the first stage,
and reducing the signal source resistance and
equalizer element impedance. High voltage gain is
provided in the following stage by a bootstrap cir-
cuit. The output stage is a complementary sym-
metrical SEPP circuit. The high voltage utility
factor of the SEPP circuit provides a high maxi-
mum output voltage. Dynamic range of the
equalizer amplifier is therefore wide and overload
input level at 0.005% distortion is 300mV (rms at
lkHz).
tNHMrl
ToneControl
Fig. 4-4 shows the basic configuration of the
circuit. This circuit is an NFB type tone control
with IC(HA12017P).
Tonecontrol (BASS,
TREBLE) isaccomplished
by providing the tone amplifier NFB circuit with
a frequency selective characteristic. The capaci-
tance
of C7-C4 arechanged
by theTURNOVER
switches
(by addinganother capacitorsin parallel)
to provideselectionof the frequency.
The NFB circuit is changedto a flat frequency
characteristicwhen the TONE switchin the OFF
oosition.
Fig.
4-3 Phono
Equalizer
Amplif
ier
Tone
Control

Power
AmPlif
ier
Section
o Amplifier Circuit
The basic circuit arrangement of the power
"-pilii"t it shown in Fig' 4-5' The-first stage
is a
aiti*""ti"f amplifier comprisingPNPtwin transis-
i.t te2l, the load circuit of which is a current
;*;; employing an NPN twin transistor(QB)'
Thecurrentmirrorprovidespush-pulloperationin
this stage,
which serves
to canceleven
harmonics
andfurther increase
gain'
-- Qf in the input &cuit absorbs
outflow of base
current from Q2, and prevents
the generation
of a
DC voltage. Because
Q1 follows any temperature
drift in Q2, temperaturedrift of the centerpoint
voltage
isPrevented.
The pre-driver
stage
(Q4, Q5) is.
a Darlington
**g"-".rt, the load circuit of which employsa
constant-currentsource(Q6)resultingahighvolt-
age
gain.
" Tite power stage
biasvoltageis suppliedby the
high spe"a bias sewocontrol circuit' The high
speea bias servocontrol circuit provides non-
,^*it"t ing operation in the power stage
(refer to
;'High Speea
Bias
Servocontrol
Circuit")'
The powerstage
(Q7
- Q12)
isa.2-stage
Darling-
ton arrangement,tite tinat stage
is parallel SEPP
circuit. Bicause there is no time constant in the
NFB circuit in the low frequencyregion' amplifi-
cation is possibledown to DC (DC inputs will be
""l.it, however,
by the input couplingcapacitor)'
o High Speed
BiasServocontrol Circuit
By operating the power stage.only within the
active region 1no possiblecut-off).and with mini-
mum idle current,'the high speed
bias
servocontrol
circuit prevents the generation of switching dis-
tortion andreduces
heatloss'
This circuit is outlined in Fig' 4-6' Whenthere
is no signalapplied to the circuit' Q1 and Q2 are
almost iut off' while Q3 and Q4 will be on' The
uoitug" across
the collector and baseof both of
these transistors
(Q3 and Q4) at this time may be
disregarded.
Consequently,with the power stage
||'.l
*lI
nl
biascircuit consisting
of 4 PNjunctions formed by
Q3,
D3 and
Q4,
and
VR1'
--Witft R1 and D1 ensuring a constart flow of
current, the base of Q1 and point X may be
brought to the same level on an AC basis(level
fluctuationsduetothesignal)byasimpleshiftin
DC level. Furthermore, Q1 may be considered
"-iti"t-toffower with R3 as
the emitter resistance'
- When the voltage across
points Y and X is in-
creased
by the positive portion of th.esignalap-
;i*i-;" itrls cirluit, it becomel.
the input signal
it-trri, emitter_follower (Q1). since the emitter-
followervoltagegainispracticallyl,avoltage
moreorlessequaltothatoftheinputsignal
iirr"i it, the voltage
increase
across
points Y andX)
ir^*"J"""a at R5. And the R3 voltageisthe volt-
age applied acrossthe base and collector of Q3
which forms part of the powerjt"g: Pi"t circuit'
il;h" biasvoltageapplied to Q3 will bein excess
by the sameamou"i ttt" voltage across
points Y
and X increased
(by positiveportion.of the signal)
above the voltage level when no signal is being
applied. Consequently, the increase 1" l:]1"?:
lii"t. o.i"ts Y and X cancels the decrease
rn
toii"g"'u"t"ss points X and Z't}r,ereby
maintaining
the idle current without cutiing the PNP power
PRE-
OR
I
VER
t'n.
d-d "easi"
Clrc,itrv
of Non-switching
Amplifier
Power
AmPlifier
Circuit
F
is.
4-5

stage off (noting that there actually is a slight de-
creasein current). For the negative portions of the
signal, Q2 and Q4 are operated in the same man-
ner, thereby preventing the NPN power stagefrom
being cut off.
4.4 DISPLAY
CIRCUIT
Power lndicator Circuit
The SX-3900 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. 4-7
.'lhe output circuit signalis first passed
through a low-pass filter and a compressor circuit
before being applied to pin no.6 (4) of the IC
(TA7318P-A). The compressor circuit makes use
of the non-linearity of risingportion of the diode's
Vd-Id characteristics to contract the signal dynam-
ic range by 20dB. The IC contains a detector cir-
cuit, compressor (40dB), and peak hold circuit for
both left and right channels. The dynamic range
of the signal is thus contracted by 6OdB to obtairr
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 voltage com-
parators. These comparators are biasedat increas-
ing levels, so each comparator will commence to
operate separately as the input level increases.
And since these comparators apply the voltages
to
the output power indicator segments,each succes-
sive segment will light up in tum asthe input level
rises.
LPF
FM-AM SELECTION FL TUBE
SIGNAL
Fig.
4-9 Frequency
Display
Circuit
tc (fA7318P-At 1/2
AM LOCAL
OSC,S
I
GN
AL
FM LOCAL
OSC,S
IGNAL
tc ( HAi2oro
)
-- -- trn Dtr !! !I EE trn Dt]
tll
O.O1 O.1 1 10 pO
FL TUEE
Fig.4-7 Power
IndicatorCircuit
5;6141+O---1-t!rr-f{
'|N++
tm
7r7
I fltl E- -fl
I
w(8rl
) o.oo1
sx-39ocl
Frequency
Display
Frequencies
receivedby the SX-3900 are dis-
played in digital form by fluorescent indicator
tube (FL tube). Eachdigit employsup to 7 seg-
ments
(a
- g) (see
Fig.4-8) to display
allnumerals
from 0 to 9 (with the exceptionof the left hand
digit whichemploysonly 2 segmentsb andc).
o
F
Fig.4-8
7-SegmentDigitDisplay
The signalsource
during 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 subjected to frequency divi-
sion (1/8 for AM and 1/80 for FM) before being
applied to the frequency counter IC (PD5009).
This IC is responsiblefor the dynamic drive of the
7-segment 5-digit display (each digit being tumed
on accordingto time-shared
sequentialscanning).
rc
(P05009)
rc
(M54451P)

D5 D4 03
Vcc GNO
Fio.4-10
Block
Diagram
of
Counter
lC
(PD5009)
An outline of the composition of PD5009 is
givenin block diagramform in Fig' 4-10'With the
FL tube a- g segments
(anode)
for each
digit con-
nected in parallel,the D1 - D5 time divisionpulse
;i;"dr (rel nig.4-11) applied
to each
grid (inde-
G;J""i grid ior each digit) result in .the digits
being Iit up in succession
from the left hand side'
nacf,"
aigit is lit up for 1ms during each5ms
inter-
tul. Pin"no.? of PD500g
is the brightness
selector
terminal. The time division pulse width is set to
;00u; for H levelinput signals,
and
to 200ps
for
L Ievel signals,
therety varying the degree
of FL
tube brightness(by varying the segment
lighting
perioa)."Note that sincethe power indicator FL
iune is driven by static drive, the degree
of bright-
,r"rr rrruy
bevaried
by changing
the gridvoltage'
ffre f.f ZUHz crystal oscillator generates
the
basic signal used in the preparation of the time
aiuirlon.-p.tlsesignaland the counter gate circuit
controlsignal.
FROM --
PRESCAL
AR
Table
1
TerminalsS1
- 54 (pin nos'3- 6)^are
used
in
d"i;;;tt"; reception mode' The 2 reception
;;d"t emptoved
in the SX-3900
(see
Table1) are
;;;;;;J bv varving the combination of input
;;;i; iH uni l;' -rri" s different IFs during FM
;.;; )re required in coping witir ]f offset in the
IF ceramic filter stage,53 and 54 being preset
arrring FM mode acc-ording
to the ceramic filter
characteristics.
"^'Aftfto.,gft the SX-3900 FM stagequartz-lock
.Vrt"- is
"capable
of locking any frequency within
;ir;FM bani, the 10kHz digit (digitin the second
decimalplace)intheFMfrequencydisplaywill
appear
onlYas
5 or 0'
.*htu fr"qrrerr"ydisplayFL tube-also
incorporates
ttre iUNf-fqC ana ^SiCXaL inclicators' And al-
though the segments
(anode) for these indicators
ur" ,iuti" driven uy itre correspondingdrive cir-
",ritr, tf," grid is driven according
to the D3 time
liilit" pu"lse
timing, therebyplacing
the segments
;;J", djnamic a'iul' ttt addition' the AM andFM
indicatorsinthelrequencydisplaysectionarelit
according to the OS timing' while the kHz and
MHzindicators
are
lit according
to theD1 timing'
DIGIT DRIVER
B
R
IGHT
NESS
SE
LECTION
MULTIPLEXER
coNTROL
CIRCUITLATCH
LOAD
GATE
PRESETAALE
5'DIGI'T
DECIMAL COUNTER
DECI
MAL
COUNTER
22-BlT x 16 ROM
lntermediate
f
requencY
10.67MH2
'10.70MH2
10.73MH2
Fig.
4-1
1 D
isit
Signal

TUNING lndicatorCircuit
The TUNING indicator consists of a center
tuning indicator (which lights up when a broad-
casting station frequency is properly tuned) and
2 detuning direction indicators which indicate the
direction in wnich the station hasbeentuned away
from. The corresponding drive circuits are out-
lined in Fig.4-72.
The TUNING indicator is activated once the
station has been tuned to within t100kHz of the
center frequency. This is because Q16 is turned
on and Q21 turned off (resulting in the detector
differential amplifier [Q19 & Q20] being turned
off and Q24 being turned on) by the FM muting
signal appearing at pin no.13 of the IF system IC
(PA3007-A) and passed via the Schmitt circuit
(Q17 & Q18) when the station is tuned away by
more than t100kHz.
The DC voltage on pin no.4 of PA3007-A
describes
an 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 polarity detec-
tor switch circuit (Q22 & Q23).
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
be higher than that on pin no.2. The Q20 collector
voltage will thus be lowered and the Q19 collec-
tor voltage raised, resulting in Q23 being turned
on, and the higher frequency (right hand side)
detuning direction indicator also being turned on.
When, on the other hand, the broadcasting fre-
quency 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 Q22
being tumed on to light up the lower frequency
(left hand side) detuning direction indicator. Wherl
either Q22 or Q23 is on, the Q24 basevoltagewill
be high, resulting in Q24 beingtumed on and Q25
turned off, which means that the center tuning
indicator will not be lit up.
Once the broadcasting frequency hasbeen tuned
properly, the voltages on pin nos.2 & 4 will be
equal. Consequently, Q22 and Q23 will both be
turned off, which means that neither of the detun-
ing direction indicators will be on in this case.
And since Q24 is turned off becauseof the de-
creased
base voltage, Q25 will be turned on, and
the center tuning indicator light up. Furthermore,
C77 is charged up via R99, resulting in Q26 being
turned on, thereby lighting up the Quartz Locked
indicator LED.
sx-39ocl
SCHl,llTT
CIRCUIT
Fig.4-12
TuningIndicator
Circuit
SIGNAL
IndicatorCircuit
The SX-3900SIGNAL indicator consistsof an
FL tube 5-pointindicatordisplay. Thesignal meter
drive signal obtained from the FM IF system IC
(PA3007-A)
and AM tuner IC (HA1197)is first
amplified and then applied to the indicator drive
IC (HA12010).
This
IC contains12pairs
of voltage
comparatorssimilar to those employed in the
powerindicatorcircuit, 5 of these pairs
being
used
to drivetheSIGNALindicator
(Fig.
-13).
4.5 PROTECTIONCIRCUIT
The purpose of this
circuitisto protectboth the
speakers
and the power amplifiers.
The relay in the
output circuit is automatically opened in any of
thefollowing
cases:
1. During the "transient operations" when the
power
supply
istumed on andoff.
2. Upon detectionof a DC voltage
in the output
circuit, causedby componentfailure or acci-
dent.
3. Upon detection of an overload,
caused
by a
short
circuitin theload.
MutingOperation
when
Power
Supply
is
Turned
OnandOff
With reference to Fig, 4-74 when the power
supply is turned on, Q5 turns off due to -B (The
time constant of the -B circuit is very small.).
If thereis no input (DC) on Q3 andQ4, they will
be off, and the timing capacitor C4 charges
up
through R8 and R7, andthus Q6 turns on. When
Q6 conducts,the relay operates,
and the output
mutingon thepower amplifier
will be
removed.
When the power supply is turned off, -B will

lc (
HA12010
)
Fig.4-13 Signal
Indicator
Circuit
abruptly decay,and Q5 will conduct owing to the
residui component of +B. As a result, C4 will
rapidly discharge, Q6 will cease
to conduct,where-
upon the relay will become de-energizedand
restore
muting.
DCVoltage
Detector
The output circuit is connected
to the Q3 emit-
ter and qa trase
via a low-pass
filter (R5, C2)'
Any DC voltagesappearing
the output circuit of
the power amplifier, it will be applied to the Q3
emitter and Q4 base.
If the voltage
is positive,Q4
turns on. C4 will rapidly discharge'
If the voltage
is negative,
QB tums on' C4 will rapidly discharge'
As consequence, Q6 will turn off and the relay
will becomede-energized,
thus causing
the output
circuitto oPen.
Overload
Detection
The overload detector circuit incorporatesthe
load (RL) in oneside
of a Wheatstone
bridge
(see
Fig. 4-15). The base and emitter of a sensing
tra'nsistor (Q2) are connected to the opposite
cornersof ttre bridge, so if RL decreases,
Q2 will
become forward biased.If RL falls below a pre-
scribed value, Q2 will turn on' C4 will rapidly
discharge.
As consequence,Q6 will tum off and
the relay will become de-energized,
thus causing
theoutput circuitto oPen.
Fig.
4-15 Overload
Detector
Fiq.
4-14 Protection
Circuit

5.
DISASSEMBLY
Wooden
Cover
Remove the two screws (O o.r each side of
the wooden
cover.
Bottom Plate
Remove the thirteen screws Q to detachthe
bottom plate.
Front
panel
sx-39ocl
Front
Panel
Remove all the knobs by pulling. liemove the
two screws
@ from the top edgeof the front panel.
Remove
the two nuts @ from the control shafts.
4.6 SURGECURRENTSUPPRESSOR
Since the SX-3900 employs a large toroidal
power transformer and two 15,0009F capacitors
in the power supply circuit, the sudden surgeof
current when the power supply is turned on may
reach severalhundred amperes. The surge current
suppressor circuit used to reduce this sudden
surgeisshown in Fig.4-16.
Whenthe POWER switch
(S1)is OFF (i.e.
no
supply of AC power), the relay contact (S2) is
open. But when this switch (S1) is tumed ON,
the suddensurge
of current is passed
through R1-,
thereby greatly reducing the flow of current.
When the output DC voltageof the power supply
circuit reachesa certain prescribed level, 52 will
close,
and R1 consequentlybeby-passed.Thetime
requiredfor this to occur,however,isconsiderably
shorter than the time required for the muting
circuit to operatewhenthepower
supply
is
tumed
on, so there isno undueeffect upon normal opera-
tion of the receiver.
Microtemp is a temperature-sensitive fuse
coupled to R1. If 52 fails to closedue to an
abnormality in the power supply circuit or relay,
the heat generated
in R1 will causeMicrotemp to
below,thereby openingthe primary circuit.
When the POWER
switch (S1) is tumed OFF,
the relay drivingcircuit is opened,thereby opening
52 andthe primary circuit.
.tt '- \
\-- 7
'-=.::att/7
\ )rt"
S
Bottom plate
RELAY
Fig.4-16 Surge
CurrentSuppressor
Circuit

6. PARTSLOCATION
Front Panel
View
Fluorescent
indicator
tube
AAV-OO8
Front panel
assembly
AN8.861
Knob (SPEAKERS)
AAD.226
Knob
(BASS,
TREBLE,
TURNOVER)
AAB-239
Wooden
cover
The A marh found on some component parts indicates
the iiportance of the safety factor of the part' There-
fore, when replacing, be sure to use parts of identical
designation.
Knob
(FILTER,FM,
BRIGHT/DIM}
AAD.227
Fluorescent
indicator
tube
AAV-OO7
Knob
(FUNCTION)
AAD-226
Knob (TUNING)
AAA-065
Knob (LOUDNESS)
AAD-227
Knob
(MODE,
MUTING)
AAD.1
39
'Knob
(VOLUME)
AAB-238
Knob
(BALANCE)
AA8-239
Lamp with wires
AEL-069
Lamp
with wires
AE L-095
Lampwith wires
AEL-069
Tuning
shaft
assemblY
AXA-260
Pushswitch (LOUDNESS)
ASG-230
Lever
switch
(MUTING
-2OdB}
ASK-1
52
4-gang
variable
resistor
(VOLUME)
ACW-304 Leverswitch (MODE)
ASK.152
variable
resistor
(BALANCE)
ACT-133
Remote
lever
switch
(TAPE
MONITOR)
ASX.1
31
Remote
leverswitch (ADAPTOR, DUPLICATE)
ASX.128
minal
(PRE
AMP
OUT/POWER
AMP lN)
AKB-063
,ATerminal
(SPEAKERS)
-AKE-054
I AC socket (AC
OUTLETS)
AKP-041
I AC power cord
ADG.O29
Terminal
(TAPE,
ADAPTOR)
AKB-063
AMM-087
knob(POWER,
TONE,
ADAPTOR,-
DUPLICATE,
TAPE
MONITOR)
AAD.1
39
FrontView with Panel
Removed
Push
switch
(BRIGHT/DlM)
ASG-230
Dual
push
switch
ASG-229
Lamp with wires
AEL-047
Phone
iack (PHONES)
AKN-O30
Remote
switch (SPEAKE
RS)
ASX-137
,ALeverswitch (POWER)
-nsr-soz
Slide rotary switch
(BASS
TURNOVER}
ASE-1
25
2-gang
variable
resistor
(BASS)
ACT-134
Lever
switch(TONE)
ASK.152
2-gang
variable
resistor
(TREBLE)
ACT-134
Slide
rotary
switch
(TREBLE
TURNOVER)
ASE-126
Rear
Panel
View
Terminal
(INPUT)
AKB-064
Bar-antenna
ATB.624
Terminal
(AM
STEREO
OUT)
AKB-076
Terminai
(ANTENNAI
AKA-o13
16

r
c
f
\
/r
\t"-
I
I
TopViw
Rectifierassembly
AWR.211
Electrolytic
capacitor
15.O00p
F,71V
ACH-210
Bottom View
Tunerassembly
GWE-132
s)<-39clct
Speakersterminal
assembly
GW3-222
Equalizerassembly
AWM-226
Power
amplif
ierassembly
AWH-097
Detector assembly
GWX.463
Tuner
assembly
GWE-132
Indicator
assembly
AWV-OO8
Lamp socket
AKK-OO5
Lamp (wedge
typel
AEL.029
Toneamplif
ierassembly
GWG-140
r t;!

1.
2.
3.
4
5.
7. DIAL CORDSTRINGING
Removethewooden cover
andthefront panel.
Turn the tuning capacitorshaftfully clockwise.
Fix the tuning drum to the tuning capacitor
shaftsothat the set-screwisuppermost.
Tie oneendof the dial cord to the spring.
Pass
the cord through the cutout section in
the tuning drum. Wind it ll2 turn around the
tuning drum, and then take it over pulleys
A, B, C,D and E in that sequence.
Wind the cord aroundthe tuning shaft3 times.
Pass
it over pully F, wind it aroundthe tuning
drum 2 times, and finally tie it to the spring
sothat it is
tensioned.
Tuningcapacitor
E
\D
Dial
pointer
7" Tum the tuning shaft and check that the cord
moves
smoothly.Cut off anyexcesscord.
8. Tum the tuning shaft counter-clockwise
as
far asit will go.
9. Align the dial pointer with the starting
point of
the dial scale (third division from the left),
andthen pass the cord overit.
10. Check that the dial pointer is in line with the
starting
point of the dial scale.
11.Finally applythe lockingpaint to the knot of
thecord
andthedial
pointerconnection.
12.
If the tensionof the cord is weak, move the
springto theprojection B.
Spri
ng
o.
Tuningdrum
Dial
pointer
connection
Tuningdrum
B
Tuning
shaft
1A

8.
ADJUSTMENTS
8.1 AUDIO
SECTION
Power
Amplifier
Turn VRS, VR5(L) and VR4, VR6(R) fully
around in the counter-clockwisedirection,
but set
VR1(L) and VR2(R) to the center positions.
Without any load or input signal,tum thePOWER
switch
ON.
o DC Balance
1. Adjust VR1(L) for 0V(to within t30mV)
betweenterminalNo.30and
ground.
2. Adjust VR2(R) for OV(to within t30mV)
between
terminal
No.29and ground.
o Idle Cunent
1. Adjust VR3 (L) for 56mV between
terminals
No.12(+)
and
No.11(-).
2. Adjust VR4 (R) for 56mV betweenterminals
No.9(+)
and
No.10(-).
3. Adjust VRb(L) for 70mV between
terminals
No.12(+)
and
No.11(-).
4. Adjust VR6 (R) for 70mV betweenterminals
No.9(+)
and
No.10(-).
Powertransformer
sx-3s|clcl
Output
Power
Indicator
Calibration
1. Apply a IkHz signalto the POWER AMP IN
terminals (or any other input power amplifier
input terminals).
2. Adjust the level of this input signal so that
the voltage on the output terminals (SPEAK-
ERS)
read
8.95V(rms).
3. Adjust VR1(L) and VR2(R) so that the out-
put power
indicatorread
10watts.
rz
ir
3ozg
ro
'g
lnd
icator
assembly
VRs
VR3VR1 vR2VR4VR6
Fig.
8-1 Power
amplif
ier
adjustments
19

8.2 TUNER
SECTION
FMTuner
o Connect the FM SG (FM signal
generator)to
the FM ANTENNA 300Q terminals
via a 300O
dummy antenna.
o Switchthe FUNCTION selector
to the FM posi-
tion, the FM MUTING OFF switchto the OFF
position.
o L5 and L6 are corelesscoils which may be
adjustedby extending one turn of coil out to-
wards
tuning
capacitor
(see
Fig.8-2).
1. Set
the SX-3900
dial pointerto afrequency
in
the 106MHz region so that there will be no
input signal.
2. Rotate the N core of T2 so that the voltage
between
no.Bandno.7 terminals
on the tuner
assembly
isreduced
to DC 0V.
3. Next tune the dial pointer to 106MHz,
and
set
the FM SG outPut to 106MHz, 60 to 80dB
(modulation
- 40OHz,
t71kHz deviation).
4. Adjust TC1 so that the voltage
between
no.8
and no.7 terminals
is reduced
to DC 0V and
maximum
reading
of the SIGNAL indicator.
5. Then tune the dial pointer to 90MHz,andset
the FM SGoutput frequency
to 90MHz.
6. Rotate the L8 coresothat the voltage
between
no.B and no.? terminals
is reduced
to DC 0V
and maximum readingof the SIGNAL indica-
tor.
7. Repeatsteps
3 to 6 above.
8. Reset
the FM SG output levelto 20- 30dB'
and adjust
"1C2,
"1C3,
TC4 and
T1 at 106MHz,
and
L2, L5 andL6 at 90MHz
in thesame
man-
ner as describedin steps
3 to 7. These
adjust-
ments will ensure
optimum sensitivity
between
the two extremefrequencies.
9. Retuneto aposition with no input signal.
10.Rotate the A core of T2 so that the voltage
between
no.8 andno.7 terminals
is reduced
to
DC OV.
11.Set the FM SG output to 98MHz and 60dB
(modulation
- 4O0Hz,
x7lkHz deviation), and
tune the SX-3900
to this position(fine adjust
the tuning knob to ensure a DC 0V reading
between
no.8and
no.7terminals).
12.
Then rotatethe B coreof T2 to reduce
distor-
tion in the demodulator
output (TAPE REC
terminal)
to minimum.
13.Repeatsteps
9 to 12above
until both specifica-
tions are
satisfactorilY
met.
14.Set the FM SG output to 98MHz and 60dB,
and
tunethe SX-3900
to thisposition.
1-5.
Adjust VR2 so that the SIGNAL indicator
(5-point
display)
reads"5".
16.
Turn the FM MUTING OFF switchto theON
position, and set the FM SG output levelto
20d8.
17.Adjust VR1 to bring the input level to the
starting
point of themutingoperation.
MultiPlex
Decoder
o Connect
the MPX SG(FM multiplex generator)
to the FM SG
external
modulator
terminal.
o Set the FM MUTING OFF switch to the OFF
position.
18.Set the FM SG output to 98MHz and 60dB
(unmodulated),and tune the SX-3900
to this
position(fine adjust
the tuningknob to ensure
a DC 0V reading
between
no.S and no.7 ter-
minals).
19.Adjust VRb to obtain a 76kHz signal
attermi-
nal
no.6.
20.Set the FM SGoutput levelto 60dB,andthe
modulation mode to external.
Then with the
MPX SG, set Main off, and pilot signal
to
t7 .lkHz deviation.
21.Adjust VR4 to reduce
leakage
of the 19kHz
pilot signal
(in both channels)
to a minimum
(atTAPEREC
terminals).
22.Setthe FM SGoutput levelto 80dB,
the MPX
SGMainto 1kHz,L+R to t67.1kHz deviation,
andpilot signal
to !7 .1kHzdeviation.
23.Rotate the T1 core around by up to 90' in
either direction to reduce the demodulator
output (TAPE REC terminals)
distortion to a
minimum.
24.
Thensetthe FM SGoutput levelto 60dB,
the
MPX SGMainto 1-kHz,
L (or R) to 133'75kHz
deviation,
and pilot signal
to x7.1kHz devia-
tion.
25.Adjust VR4 to reduce
crosstalk
between
L and
R channelsto a
minimum.
20