Pioneer TX-9800 User manual

etvice
c
/Vlanual
AM/FM STEREO TUNER
TX=-93800
Y PIONEER’
i a

MODEL TX-9800 COMES IN FOUR VERSIONS DISTINGUISHED AS FOLLOWS:
Voltage Remarks
120V U.S.A. model
110V, 120V, 220V and 240V (Switchabie) General export mode!
110V, 120V, 220V and 240V (Switchable) U.S. Military model
220V and 240V (Switchable) Europe or Oceania mode!
© Although the basic features of KU, S, S/G and HG types are the same. The major difference is
in appearance, KU, and S/G types being fitted with wooden case, while S and HG types
employ metal cover.
@ This service manual is applicable to the KU type. When repairing the S and S/G types, please
see the additional in this service manual (p37 — p43). When repairing the HG type, please see
the additional service manual (ART-347-0).
CONTENTS
1. SPECIFICATIONS ............ 000002 eee 3 Additional Service Manual
2. FRONT PANEL FACILITIES.............. 4 1. SPECIFICATIONS ........... 2.000880
3. BLOCK DIAGRAM............0. 0000 enue 5 2. CONTRAST OF MISCELLANEOUS PARTS ....
4. CIRCUIT DESCRIPTIONS 3. SUPPLEMENTS FOR S AND S/G TYPES
4.1 Signal Circuit... 2.2.2.0... ee eee 5 3.1. Schematic Diagram ....... 602?
AD SWAPO CHOU uns ea won amstettn eee 7 3.2 Tuner Assembly (GWE-116) .. - +--+ >>
4.3. Control Circuit... 0.0.0.0... 00.000 ae 9 3.3 LED Assembly 1 (GWX-252). . - sss
44 AMTuner...... 0.2.20 eee eee ee 11 3.4 LED Assembly 2 (GWX-253). . - +--+ +++:
DISASSEMBLY sc3cuacde venues vous Mawes 12 3.5 Switch Assembly (AWX-113) . - +--+ =
6. DIALCORDSTRINGING ................ 13 3.6 Power Supply Assembly (AWR-190)
7. ADJUSTMENTS
7.10 AMTuner .... 2. eee 14
FZ” EM Tune on eae eee oh ee a aes ke 15
8. PARTS LOCATION ............ 00000 18
9. EXPLODED VIEW ................000. 20
10. SCHEMATIC DIAGRAM P.C. BOARD
PATTERNS AND PARTS LIST
10.1. Miscellanea... ... ee ee 23
10.2 Schematic Diagram ..............0.0. 25
10.3. P.C. Board Connection Diagram......... 28
10.4 Parts List of P.C. Board Assemblies....... 31
TA PACKING 2... ods ctotnd selene a halw aes 34

1. SPECIFICATIONS
Semiconductors
FM Section
Usable Sensitivity .......
50dB Quieting Sensitivity . .
Signal-to-Noise Ratio
at 85dBf ...........
Distortion at 85dBf......
Capture Ratio...........
Alternate Channel Selectivity
Stereo Separation ........
MONO: 8.8dBf (1.5uV)
MONO: = 13.2dBf (2.5uV)
STEREO: 36.1dBf (35uV)
MONO: = 83dB
STEREO: 80dB
MONO: 100Hz 0.05%
1kHz 0.04%
10kHz 0.06%
STEREO: 100Hz 0.1%
1kHz 0.07%
10kHz 0.2%
WIDE NARROW
eteNaege ye 0.8dB 2.0dB
puede ane et 30dB 85dB
TkHz: 55dB
20Hz to 10kHz: 40dB
Frequency Response .....
Spurious Response Ratio . .
Image Response Ratio ....
IF Response Ratio.......
AM Suppression Ratio ....
Subcarrier Product Ratio ..
Muting Threshold .......
De-Emphasis Switch
(Switchable).........
Antenna Input .........
AM Section
Sensitivity
IHF, ferrite antenna. ...
IHF, external antenna . .
Selectivity ............
Signal-to-Noise Ratio... ..
Image Response Ratio ....
IF Response Ratio.......
Antenna .............
Audio Section
Output (Level/Impedance)
FM (100% MOD.) .....
20Hz to 10kHz £0.2dB
20Hz to 15kHz +92 dB
110dB
120dB
110dB
65dB
70dB
19.2dBf(5uV)
25us ~ 75ys
300ohms balanced
75ohms unbalanced
300uV/m
15yuV
WIDE; 20dB
NARROW; 50dB
55dB
70dB
65dB
Ferrite Loopstick Antenna
FIXED: 650mV/4.2kQ
VARIABLE: S0mV to
1.3V/3.6kQ
AM (30% MOD.)...... FIXED: 200mV/4.2kQ
~ VARIABLE: 15mV to
400mV/3.6kQ
Multipath
V (Vertical)......... 300mV/10kQ
(AM 1kHz 30% MOD)
H (Horizontal) ....... 400mV/7kQ.
(FM 1kHz 100% MOD)
Miscellaneous
Power Requirements ..... 120V 60Hz only.
Power Consumption ..... 28W
Dimensions ........... 453(W) x 155(H) x390(D) mm
17-11/16 x 6-1/8 x 15-3/8in
Weight) so. ..005. 25003 29 Without Package:
9.3kg (20Ib 802)
With Package:
10.7kg (23lb 90z)
Furnished Parts
FM T-typeantenna................0002 cee eee 1
Connection Cord with Pin Plugs.................. 1
Operating Instructions ................0...000- 1
NOTE:
Specifications and the design subject to possible modifica-
tion without notice due to improvements.
POWER SWITCH
Set to ON position to turn on power. Pilot lamp will light up.
SIGNAL METER
This meter indicates the antenna input level of the AM
and FM broadcasting waves. The higher the input level,
the more the meter deflects toward right. When selecting
the desired station, find the position of the tuning knob
which effects the maximum deflection of the meter
pointer. When selecting an FM station, also observe the
tuning meter to determine the optimum tuning point.
TUNING METER
This meter indicates the optimum tuning point irrespec-
tive of the field strength when selecting an FM station.
With no signal, the pointer remains at the center; as a
signal is tuned in, it deflects to the right or left; when the
signal is tuned in accurately, the pointer will correctly
move to the center of the scale. If the tuning knob is ad-
justed further, the pointer deflects to the right or left; as
the signal moves off completely, the pointer returns to the
center position again.
MEMORY MARKERS
Convenient for designating most often tuned in stations.
Slide markers with fingertip to desired positions.
2. FRONT PANEL FACILITIES
FM/AM INDICATORS
These indicators light up during an FM or AM reception,
respectively.
FM-LOCKED INDICATOR
With the function switch set to FM and the FM muting/
mode switch set to ON, this indicator lights up when you
take your hand off the tuning knob at the optimum
tuning point. This light indicates that the quartz locking
circuit has been activated by the built-in touch sensor de-
tector circuit and the frequency of the circuit is locked to
the frequency of the station.
FM-TUNE INDICATOR
This indicator lights up when the optimum tuning point is
obtained.
FM-STEREO INDICATOR:
This indicator lights up when ‘the tuner is receiving a
stereo program if the FM MUTING/MODE switch is set to
AUTO.
Pilot lamp
isle =|
OUTPUT LEVEL KNOB—
This
knob
is
used
to
adjust
the
output
level
of
the
variable
output
jacks.
When
it is
rotated
in
the
direction
of
MAX,
the output level is increased.
TUNING KNOB
This
knob
is
used
for
selecting
stations.
When
selecting
an
AM
station,
observe
the
signal
meter,
and
when
selecting
an
FM
station,
observe
both
the
signal
meter
and
the
tuning
meter.
FUNCTION SWITCH
This
switch
is
used
to
select
the
type
of
broadcasting
waves.
FM.... Forreception of FM broadcasting
AM.... For reception of AM broadcasting
=i
Tx-9SsoO
MPX NOISE FILTER SWITCH
If a comparatively high frequency noise is noticed during
reception of a stereo program, this switch is set to ON.
Stereo separation will thereby somewhat deteriorate.
This switch should normally be kept OFF.
FM MUTING/MODE SWITCH
When this switch is set to ON, unpleasant interstation
noise is eliminated, which makes selection of stations
easier. However, if the muting switch is set to ON in areas
where the field strength is extremely weak, the station be-
ing received may also disappear. In such areas, therefore,
the muting switch should be turned OFF. When this
switch is set to OFF, monaural reception will be obtained
even though the station is broadcasting a stereo program.
FM-AM IF BAND SWITCH
FM and AM IF (intermediate frequency) passband can be
set to for wide or narrow.
This switch is used to select between NARROW (narrow
band) and WIDE (wide band). In this way, it is possible
to change over the pass bandwidth of the intermediate
frequency signals.
NARROW ... When tuning in the desired station, and if
adjacent station interference is a problem
at the WIDE setting, set switch to this
position.
WIDE...... Set the switch to this position after the
desired station was received without ad-
jacent station interference.

3. BLOCK DIAGRAM
[” FM FRONT ENO aae
ANTENNA SINGLE
INGLE DOUBLE
eae TUNE TUNE
750
soon! fea | Leo pelea eae fi
/t BUFFER
AMP
SAMPLING | [BUFFER
HOL D AMP
Xtal PULSE
osc [Jf * “64 Flrormine
APC
AM
apitenna! [SINGLE
©
TUNE ° (2)
{ SINGLE
| TUNE
ee
a
AM TUNER —
4. CIRCUIT DESCRIPTIONS
4.1 SIGNAL CIRCUIT
FM Front-end
The FM front-end of this set uses a precision
frequency-linear type 5-ganged tuning capacitor.
The circuit is shown in Fig. 4-1. The antenna
input is made an unbalanced (752) by an M-
coupled single-tuned circuit. The RF stage uses two
dual-gate MOS FETs (Q,, Q,) having superior high-
frequency characteristics. The interstage tuning
circuits are C-coupled double-tuned for improved
reception. The phase characteristic, spurious
interference ratio, and IF interference ratio are
especially good. A dual-gate MOS FET (Q;) is
also used at the mixer stage. The received signal is
applied to gate 1 and the local oscillator signal is
input at gate 2. The converted output (10.7MHz)
is taken from the drain and applied to the IF
amplifier thru an IFT. The local oscillator (Q,) is
modified Clapp circuit. Its output is fed to the
mixer.
D, of the local oscillator is a vari-cap diode that
forms part of the tuning capacitance. A vari-cap
diode is an element whose capacitance can be
controlled by means of the impressed voltage, and
is designed to control the voltage relative to local
oscillator frequency deviation to within +100kHz.
This control voltage is obtained from an APC
LOCAL osc
(vco)
FM IF AMP
poe
roe ir DIODE
H SWITCH
ii
TUNING
KNOB
\\
Z
J
ZA
Q
Touch | |RecTIFIER | [SCHMITT
SENSOR | |
}
\"§ SENSOR GAIN
BUFFER
AMP
------------ ------------5
ie; =
(Automatic Phase Control) circuit. (See the de-
scription of the APC circuit on page 7.)
IF Amplifier
This tuner employs a dual IF amplifier consist-
ing of a wide band IF amplifier designed for high
separation, low distortion reproduction, and a
narrow band IF amplifier used for rejection of
interference signals (Fig. 4-2).
The wide band IF amplifier has been designed
with the minimum number of frequency selective
elements, with emphasis being placed on linear
phase characteristics. The narrow band IF amplifier
on the other band, has been designed with em-
phasis on selectivity. When the selector switch is
in the wide position, the signal path is FM front-
end > Q, > F, > Q,> T, > Ds, Ds > PA8001-A,
while in the narrow position it is FM front-end
> Q, > F, > Q, > T, > D, > narrow IF amp. D,>
PA38001-A. The changeover between wide and
narrow is performed of diode switches (D, to D,).
When the selector switch is in the wide position,
D, and D, are biased in the forward direction and
D, and D, are biased in the reverse direction, thus
bypassing the narrow IF amplifier. When the
selector switch is in the narrow position, D, and
D,-are forward biased and D, and Dg, are reverse
biased.
INDICATOR
@ © @@
DIODE
q é
lie
i a
Soe eee ee ee Ae eet
= (X) ®
(PA3OOI- A)
FUNCTION
ANTENNA {
—— oF!
75Q 1
Sat
FM STEREO DEMODULATOR
(PAIOOI -
MPX
A)
ears
‘@ ©
CERAMIC
FILTER
IF
AMP
MPX
NOISE
ta
MPX NOISE FILTER
rowan EE
SEPARA- aa —
i TION fle
ricter |JcontroiL ta @ ® 6 fa
so,
IF BAND
APC +8
+8
Function|
S
VOLTAGE oo 7
| REGULATOR Oo
recririen|
CONSTANT
VOLTAGE
&) DE-
MEHASIS ouTPuT
Oi
FIXED
es
OUTPUT
LEVEL
& aa
oa
sanikate
Aon
Dx5
MULTI PATH
avs
POWER SUPPLY
Ez!
FUNCTION INDICATOR
BUFFER AMP
ee
osc
to APC CIRCUIT
Fig. 4-1 FM front-end
Q7
Fig. 4-2
FM IF amplifier
: “ae van: CAP
towe R
E —=to IF AMP
— AGC
from f CIRCUIT
NARROW
O
O
WIDE
\F BAND
+B

Multiplex Decoder
An IC (PA1001-A) developed by Pioneer is used
in the stereo demodulation circuit. PA1001-A
contains a PLL system VCO (Voltage Controlled
Oscillator), NFB demodulator, automatic pilot
conceller, and stereo/mono automatic switch.
The NFB demodulator and automatic pilot can-
celler are special features of this IC. The NFB
demodulator suppresses distortion caused by the
non-linearity of the demodulation circuit. The
automatic pilot canceller cancels the pilot signal
(19kHz) in the stereo demodulation signal. This
circuit cancels the pilot signal (19kHz) in the
stereo demodulated signal by applying the 19kHz
from the VCO synchronized with the pilot signal
(19kHz) in the composite signal to the stereo
demodulated signal thru an AGC amp. Moreover,
since the cancel signal level tracks the input pilot
signal level by means of the AGC amp., the re-
jection ratio remains the same even with changes
in input pilot signal level.
Output Amplifier
An AF MUTE IC (PA1002-A) is employed in
the final stage of the tuner. This IC contains two
AF amplifiers for L and R channels, together with
a muting gate circuit. These AF amplifiers employ
time constant NFB to provide de-emphasis charac-
teristics. The muting gate circuit is electrically
connected to the signal circuit when a DC voltage
is applied to pin no.8 of the PA1002-A (Refer to
muting control in page 10).
4.2 APC CIRCUIT
The APC circuit stablizes the receiving state by
suppressing changes in the FM front-end local
oscillator frequency.
This circuit is a PLL circuit that controls the
frequency of the local oscillator (VCO; Voltage
Controlled Oscillator) by comparing the phase
of a reference frequency produced by a crystal
oscillator and the phase of the local oscillator
frequency, and then using the DC voltage corre-
sponding to their phase difference to control the
local oscillator. The capture range (range over
M5S003P
ft XI/I6
MS3273P M53293P
6.4MHz
Ar {Ot 100k Hz
TX-9800
which
circuit
is
locked)
of
this
APC
is
approxi-
mately
+12kHz,
and
its
lock
range
(range
which
can
be
controlled
by
APC)
is
+75kHz.
Fig.
4-3
is
the
block
diagram
of
this
circuit.
to IF AMP
LOCAL OSCILLATION
SIGNAL
VOLTAGE
SAMPLING
CIRCUIT
SAMPLING PULSE
GENERATOR
Fig. 4-3 Block diagram of APC circuit
HOLD
Sampling Pulse Generator
This circuit uses 3 digital ICs and one crystal
(Fig. 4-4). The crystal and two NAND gates on
M5S008P from an oscillator circuit that oscillates
at the reference frequency (6.4MHz).
This reference frequency is converted to a
100kHz square wave by dividing it by four with
M53273P and then dividing it by sixteen with
M53298P. This 100kHz square wave is applied to
two NAND gates on M5S0038P and shaped to a
100kHz sampling pulse (Fig. 4-5). This sampling
pulse is then applied to the sampling hold circuit.
|
©) lOO kHz
O°
to SAMPLING HOLD
CIRCUIT
Fig. 4-5 Sampling pulse generator

Sampling Hold Circuit
The sampling hold circuit compares the phases
of the local oscillation frequency and sampling
pulse, and generates a voltage corresponding to
their phase difference (Fig. 4-6). When the sampl-
ing pulse is applied to the base of Q;, Q; is turned
on, and current flows thru Q,. When the pulse
is removed, Q, is turned off, and a flyback pulse
is generated at the base of Q, at this instant by
the inductance component of the circuit. C, is
charged by this flyback pulse and Q, is then turned
off. When the next sampling pulse is applied, the
charge across C, is discharged thru Q,; and C; is
recharged by the flyback pulse generated at the
base of Q; at this time. The voltage waveforms
of each part are shown in Fig. 4-7. This becomes as
shown in Fig. 4-8 when the local oscillation fre-
quency is applied to the base of Q,.
Fig. 4-8a is the waveform when the sampling
pulse and local oscillation frequency are in phase,
and Fig. 4-8b is the composite waveform when
there is a phase difference. Therefore, a voltage
corresponding to the phase difference between
the sampling pulse and local oscillation frequency
is hold. The C, hold voltage waveform is shown
in Fig. 4-9.
+B -~—_+>—
2
LOCAL
OSCILLATION +
Pao’
to
LPF,
OC
AMP
™
SAMPLING PULSE
ee
Fig. 4-6 Sampling hold circuit
SAMPLING PULSE i ens cee
FLYBACK PULSE
FET SWITCH
CONTROL
to APC BEAT
DETECTOR
Q2
BASE
!
!
'
Q2 EMITTER |
(C5 HOLD VOLTAGE)
DISCHARGED BY CHARGED BY
SAMPLING PULSE FLYBACK PULSE
Fig. 4-7 Voltage waveforms
a Local osc. signal
Flyback
pulse
Q2 base
biase
b Local osc. signai
Flyback
pulse
~<— Level according to
phase of local osc.
signal
<— Q) base biase
Y
Fig. 4-8 Q2 base waveforms
a When tuned at center of hold range
\ Standerd voltage
{Cs hold voltage)
b When focal osc. has attempted to move
to a lower frequency Standerd
SSS
ee
eer
tev
voltage
“Cs hold
r voltage
c¢ When local osc. has attempted to move
to a higher frequency “ Cs hold
voltage
~~ Standerd
voltage
d When deviated from APC lock
Cs hold
o voltage
Fig. 4-9 Cs hold voltage waveforms

4.2 CONTROL CIRCUIT
NOTE:
The control circuit is operated digitally. Consequently,
voltage changes are represented by “‘H”’ (high level volt-
age) and “‘L”’ (low level voltage) in the description.
APC Operation Control
The FET switch (Q;) in the APC circuit is
turned off when the tuning knob is touched.
During this time, a reference voltage (+8V) is
applied to the variable capacitance diode in the FM
front-end local oscillator to permit station tuning
operations with the APC turned off.
When an input signal whose antenna input level
is at least 20dBf (5.5uV) is tuned, the TUNE
indicator LED is turned on. And when the tuning
knob is then released, the FET switch (Q;) is
turned on, thereby completing the APC circuit
loop to “lock” the local oscillator frequency. The
TUNE indicator LED subsequently turns off, and
the LOCKED indicator LED turns on instead.
These operations are all controlled by the touch
sensor, APC beat detector, and the output from
pin no.12 of the IF system IC (PA38001-A). (See
Fig. 4-10).
When the tuning knob is touched by hand,
noise voltage induced by the human body is
detected and amplified by the touch sensor. The
sensor output is then rectified and employed as
the Schmitt A control voltage. When an APC beat
signal of at least 7kHz appears at the output of
the sampling hold circuit, it is detected, and then
amplified by the APC beat detector. (APC beat
signals are generated at the sampling hold circuit
output if the FM front-end local oscillator fails
APC-—PLL
Tx-9800
to remain at an integer multiple of 100kHz. The
frequency of this beat signal lies within the DC ~
50kHz range, and is determined by the phase dif-
ference between the sampling pulse and the oscil-
lator frequency). The output of the APC beat
detector is rectified, and employed as the Schmitt
B control voltage. When a station is tuned away by
more than +65kHz, or if the antenna input level is
below 20dBf, a DC voltage appears at pin no.12 of
the IF system IC (PA3001-A), this also being used
to control Schmitt B.
Consequently, when the antenna input level of
the tuned signal exceeds 20dBf, the collector volt-
age of Q;, in Schmitt A will be set to “‘L’’, and the
collector voltage of Q33 set to ‘‘H’’. And with the
collector voltage of Q3, in Schmitt B at ““H”’, the
collector voltage of Q3, is also set to “H” (by the
Q3,. collector voltage). The base voltage of Q3; is
thereby increased, resulting in this transistor being
turned on to light up the TUNE indicator. Since
Q34 remains off because of a low base voltage, the
LOCKED indicator does not light up at this time.
And since Q3, has already been turned on by the
collector voltage of Q37, the gate voltage of the
APC circuit FET switch (Q;) will be low, which
means this switch will also remain off.
When the tuning knob is then released, the col-
lector voltages of Schmitt A Q3, and Qs3;, and
Schmitt B Q3, will all be inverted, resulting in Q3;
(TUNE indicator LED) being turned off, and Q3,4
(LOCKED indicator LED) being turned on. Qa. is
also turned off to turn the FET switch (Q;) on.
BUFFER vco
AMP {LOCAL OSC)
SAMPLING HOLD
CIRCUIT
FET
?,.
SAMPLING PULSE
GENERATOR
TOUCH SENSOR SCHMITT A
TUNING
KNOB Q30 Q31
POWER
TRANSFORMER
ac Line 3
TIMING TRIGGER
CIRCUIT
APC BEAT
DETECTOR
FUNCTION
Fig. 4-10 APC operation control circuit
F
[
!

Timing Trigger Circuit
This circuit is designed to delay the lighting up
of
the
indicator
LEDs
(TUNE,
LOCKED,
STE-
REO) when the power is switched on, and to turn
them off immediately when the power is switched
off again. (See Fig. 4-10).
When the power is switched on, Q2. is turned
off immediately by a negative voltage applied via
D,.- The base voltage of Q,, is thereby increased
gradually, the increase being controlled by the
Rii3/C1;3 time constant. Once the voltage reaches
+1.2V (approx.), Q,7 and Q., are both turned on,
thereby tuming on all relevant indicator LEDs.
When the power is switched off again, the
negative voltage applied via D,, is cut immediately,
resulting in Q., being turned on. C,,3; therefore
discharges directly via Q.. to turn Q,7 and Q2, off.
All indicator LEDs will consequently turn off
immediately. This same result is also achieved
when the FUNCTION selector is in the AM posi-
tion. This is due to the fact that the base of Q,, is
connected to ground by the FUNCTION selector,
thereby turning Q,7 and Q», off.
Re-lock Trigger Circuit
When the power is switched on, this re-lock
trigger circuit activates a sweep of the local oscil-
lator frequency, covering a range of up to 100kHz
both sides of the frequency indicated by the dial
pointer at the time. If a signal of antenna input
level in excess of 20dBf is detected in this range,
the frequency is automatically re-locked by the
APC circuit. (See Fig. 4-11).
In this case, when the power is switched on
Q.3 is turned off immediately by the negative volt-
age applied via D,,, resulting in the voltage changes
at different places describing different curves as
shown in Fig. 4-12. The voltage applied to the
variable capacitance diode in the local oscillator is
represented by curve (e), thereby causing the local
oscillator frequency to change, or ‘“‘sweep” within
a limited range. If an input signal whose antenna
input level exceeds 20dBf is detected during this
sweep, the APC circuit FET switch is turned on,
Fig. 4-11 Re-lock trigger circuit
10
resulting
in
the
frequency
of
that
input
signal
being
locked
by
the
APC
circuit.
Muting Control Circuits
This tuner features 3 major muting actions.
(1)
Inter-station
muting
in
the
FM
band
and
mut-
ing of weak FM stations.
(2)
Muting
of
switching
noises
when
FUNCTION
selector
and
IF
BAND
switch
are
operated.
(3)
Muting
when
POWER
switch
is
turned
on
and
off.
All
muting
action
is
controlled
by
the
muting
gate
included
in
the
AF
MUTE
IC
(PA1002-A).
(See Fig. 4-13).
(1) Inter-station Muting in FM Band
When
any
FM
input
signal
whose
antenna
input
level
is
below
20dBf
(5.5uV)
is
received
(which
also
covers
the
case
when
no
input
signal
is
re-
ceived),
a
DC
voltage
appears
at
pin
no.12
of
the
IF
system
IC
(PA3001-A).
If
the
MUTING
switch
has
been
turned
on,
this
DC
voltage
is
applied
to
pin
no.8
of
the
AF
MUTE
IC
(PA1002-A)
to
activate
the
muting
circuit.
(2)
Muting
of
Switching
Noises
(FUNCTION
Selector
and
IF
BAND
Switch)
When
either
the
FUNCTION
selector
or
the
IF
BAND
switch
is
switched
to
another
position,
the
Q,»
base
potential
is
dropped
momentarily,
result-
ing
in
Q.5
being
turned
on
during
the
same
brief
moment.
During
this
interval,
C,,,
is
charged
up,
the
charge
then
being
applied
to
pin
no.8
of
PA1002-A.
The
muting
time
is
thus
determined
by
the
C,,4/Ri15
time
constant.
(3) Power Switch Muting
The
muting
trigger
employed
when
the
POWER
7 res ON
© 2 oe
@) Cee ee ah
1 5 es ee ON
I
© ) canter
oo <
Fig. 4-12 Voltage waveforms

switch is turned on and off is formed by Q,; and
Q.;. When the POWER switch is turned on, Q,;
is tured off by the negative voltage applied via
D,.. The consequent voltage changes at points (a)
and (b) are shown in Fig. 4-14. The point (b)
voltage is applied to pin no.8 of PA1002-A. When
the POWER switch is turned off, Q.3 is turned on
due to the immediate cut off of the negative
voltage applied via D,,. Q.,;5 is then turned off as
a result of the voltage at point (a) dropping to OV,
thereby generating a muting trigger action at point
(b).
4.4 AMTUNER
The AM tuner stage is equipped with a 3-ganged
tuning capacitor and an IC (HA1197). The IF
amplifier stage includes a ‘‘wide IF amplifier’
stage (for improved quality of sound) and a “nar-
row IF amplifier” stage (for better selectivity).
(See Fig. 4-15).
The WIDE and NARROW positions are switched
by switching the bias of D,, and D,;, thereby
altering the signal path. In the NARROW position,
D,s is turned on, resulting in the inverse biasing
of D,,, and the IF signal being passed via F,
(narrow band-pass filter). In the WIDE position,
the D,, bias is removed, resulting in D,, being
biased in the forward direction, and the IF signal
being bypassed via D,,.
ANTENNA HAII97
O
TX-9800
AM
SIGNAL
( PAIOOI~A) (PAIO02~-A )
MPX OUTPUT
F MUTE IC
a
(PAZ00I—A)
FM IF
SYSTEM IC
DECORDER
1c (8)
OFE D8
+B=O
O
O
ON | MUTING
+B
POWER
TRANSFORMER
Ac LINE 3}
Fig. 4-13 Muting control circuit
POWER ON POWER OFF
oo !
i
(0) 2 ae
|
v
|
|
025 ON
© Ea
POWER ON MUTING POWER OFF MUTING
TRIGGER TRIGGER
Fig. 4-14 Voltage waveforms
a ee ep
SIGNAL
METER
PA3ZOOI-A
ARROW KPA IO0I-A
+B AM
°
WIDE +B °
IF BAND FM
FUNCTION
Fig. 4-15 AM tuner
11
Pea SE EPS RAAT, Sere NR PAY PSA CANT oe RR te NRA ee Pa

5. DISASSEMBLY
Wooden Case
Remove the two screws (A) on each side of the
wooden case.
Bottom Plate
Remove the eight screws (B) to detach the
bottom plate.
Front Panel
Remove the all control knobs. Remove the five
screws (C) from the front panel.
Wooden case
Bottom plate
12