Pioneer TX-6800 User manual

AM/FM STEREO TUNER
x<-6800
TX-60S
PIONEER

Both Model TX-6800 and TX-608 have the same basic performance. The major difference is in appear-
ance, Model TX-6800 being fitted with wooden side and top panels, while Model TX-608 employs metal.
MODEL TX-6800 COMES IN TWO VERSIONS DISTINGUISHED AS FOLLOWS.
Voltage , Remarks
120V only U.S.A. model
120V only Canada model
Voltage Remarks
120V only U.S.A. model
220V and 240V (Switchable) Europe mode!
220V and 240V (Switchable) United Kingdom model
220V and 240V (Switchable) Oceania model
110V, 120V, 220V and 240V (Switchable) General export model
110V, 120V, 220V and 240V (Switchable) U.S. military model
This service manual is applicable to the TX-6800/KU. When repairing the TX-608/KU, please see page
23, and for the other types, please refer to the additional service manuals.
CONTENTS
1. SPECIFICATIONS .......... 0.0.0.0 eae 3 9. EXPLODED VIEW
2. FRONT PANEL FACILITIES.............. 4 9.1 Exterior Components ...........0005 13
3. BLOCK DIAGRAM ............... 00005 5 9.2 Interior Components............-00% 14
4. CIRCUIT DESCRIPTIONS ; 10. SCHEMATIC DIAGRAM, P.C. BOARD
4.1 AMTuner.... 0... eee eee ee eee) 8B Pa ee RSME EARS to
RD? SENNCE ME oh wee sas bogs tala oe UO 6 10.1 Miscellanea ........... 00.0002 eee 15
5. DISASSEMBLY ...............- 2 ee ee 7 10.2 Schematic Diagram ...... 0... 2 ee eee 16
6. PARTSLOCATION ............. 2... ee. 8 10.3 P.C. Boards Connection Diagram ........ 18
7. DIALCORDSTRINGING................ 9 10.4 Parts List of P.C. Board Assemblies ...... 21
8. ADJUSTMENTS Vt. PACKING is. cee ek ek elle ce eee wi «22
Bar) PNP Raner ey tns ubetanin: Tic te 8) y 10 12. SUPPLEMENTS FOR MODEL TX-608/KU..... 23
8.2 AMTuner... 2... 0.2... cee ee eee 12

1. SPECIFICATIONS
Semiconductors
FM Section
Usable Sensitivity .......
50dB Quieting Sensitivity ..
Signal-to-Noise Ratio
at 65dBf ...........
Distortion at 6S5dBf......
Capture Ratio
Alternate Channel Selectivity
Stereo Separation .......
30Hz to 15kHz:
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 .........
3
1
8
15
MONO: 10.8dBf (1.9uV)
MONO: 15dBf
STEREO: 38dBf
MONO: 80dB
STEREO: 74dB
MONO: 100Hz 0.1%
1kHz 0.1%
6kHz 0.15%
STEREO: 100Hz 0.2%
1kHz 0.2%
6kHz 0.25%
exces Tice 1.0dB
eon 60dB
1kHz: 40dB
35dB
20Hz to 15kHz *9:8 dB
70dB
60dB
80dB
55dB
50dB
17.2dBF (4.0uV)
25us - 75us
300ohms balanced
75o0hms unbalanced
AM Section
Sensitivity
IHF, ferrite antenna ..
{HF, external antenna ..
Selectivity 2.0... 42 en55
Signal-to-Noise Ratio. ....
Image Response Ratio
IF Response Ratio ......
Antenna .......0.0005
Audio Section
Output Level
Miscellaneous
Power Requirements .....
Power Consumption .....
Dimensions ...........
Weight (Without Package) .
Furnished Parts
FM T-type Antenna ......
Connection Cord with Pin Plugs
Operating Instructions .....
NOTE:
TX-6800
. 300unV/m
15yuV
35dB
50dB
. 40dB
70dB
Built-in Ferrite Antenna
650mV/4.3kQ
(FM 100% MOD.)
120V 60Hz
14W
451(W) x151(H) x 284(D) mm
17-3/4(W)x 5-15/16(H)
x11-3/16(D) in
. 5.3 kg (111b 110z)
Specifications and the design subject to possible modifica-
tion without notice due to improvements.

2.
FRONT
PANEL
FACILITIES
ARPPER FPP PP So cc ee
$ ao 0 a EJ 100 12
iz
Te ADK
@PIONEER
STEREO TUNER TX-6800
@ POWER SWITCH
Set
this
switch
to
ON
to
supply
power
to
the
tuner.
@
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
to-
ward
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
irrespective
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
accurate-
ly,
the
pointer
will
correctly
move
to
the
center
of
the
scale.
If
the
tuning
knob
is
adjusted
fur-
ther,
the
pointer
deflects
to
the
right
or
left;
as
the
signal
moves
off
completely,
the
pointer
re-
turns
to
the
center
position
again.
@
FUNCTION
INDICATORS
These
indicators
light
up
during
an
FM
or
AM
re-
ception,
respectively.
@® FM STEREO INDICATOR
This indicator lights up when the tuner is receiv-
ing a stereo program if the FM muting/mode
switch is set to ON.
© DIAL POINTER
This pointer indicates the broadcasting stations.
@ FUNCTION SWITCH
This switch is used to select the type of broad-
casting waves.
FM ....... For reception of FM broadcasting
AM
.......
For
reception
of
AM
broadcasting
FM MUTING/MODE SWITCH
When this switch is set to ON, unpleasant intersta-
tion 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 ex-
tremely weak, the station being received may also
disappear. In such areas, therefore, the muting
switch should be turned OF F (MONO). When this
switch is set to OFF (MONO), monaural recep-
tion will be obtained even though the station is
broadcasting a stereo program.
@ TUNING KNOB
This knob is used for selecting station. When
selecting an AM station, observe the signal meter,
and when selecting an FM station, observe both
the signal meter and the tuning meter.

TX-GS00
3.
BLOCK
DIAGRAM
ae
Lc
RF
Lc
tF
ae
DEMODULATOR
@)
MIXER
SCOR
ee
tt
esate
@®® Of
hive
:
CERAMIC
FILTER
a
H
AMO— |
ea
rae
LC
|LOCAL
DE-EMPHASIS
! TUNE| OSC.
SIGNAL TUNING
} rene TUNING (STEREO/MONO) &) 75/25us
‘@
Fs
Lo]
STEREO
H
ee
/ BAR-
/ ANT.
i
--——-JLC
TUNE
fe
@
B
TRANSFORMER
vi
!
abl
FUNCTION
RECTI~
oy,
V.R. Ord OS)
f
n
(AM
OSC)
CONTROL
FIER
ae
ti
ov
/
‘@
‘@
DQ
ILLUMINATION
Qe
eee
ke
FM
AM
OS)
FUNCTION
(6)
(©)
(C)
LAMPS
HNVULEYUOUAUUVTQQUDUANIQUEDLUUOUUCUQUDULTUUUUTVOCUALLSTHUOOUTTUUUEOOEUCOOU
QUAN
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TAO
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VCORE
4.
CIRCUIT
DESCRIPTIONS
4.1 AM TUNER
The
AM
tuner
employs
a
2-ganged
tuning
capaci-
tor,
a
single-element
ceramic
filter,
and
an
IC
(HA1138)
consisting
of
an
RF
amplifier,
mixer,
2-stage
IF
amplifier,
detector
and
AGC
amplifier.
See
Fig.
4-1
for
the
block
diagram.
When
the
FUNCTION
switch
(S3)
is
in
the
FM
position,
+B
is
applied
to
the
emitter
of
Qi:
via
Rs2,
Re2
and
Res.
Qii
will
turn
off,
and
the
local
oscillator
circuit
will
be
opened.
Fig. 4-1 AM tuner

4.2 FM TUNER
Front-End
A frequency linear 3-gang variable capacitor is
used with a single stage FET RF amplifier.
The FET possesses high input impedance com-
pared with a transistor, and allows simple coupling
with the input tuning circuit, plus a significant ad-
vantage in terms of noise.
The local oscillator, Q3 employs a modified
Clapp circuit, thereby reducing the amount of
drift caused by changes in time, ambient tempera-
ture, and power supply voltage. Also since the
oscillator signal is obtained from the tuning circuit,
there are far fewer higher harmonics, resulting in
a much cleaner waveform with less spurious inter-
ference.
The oscillator signal is applied to the base of
the mixer transistor Q2.via low capacity capacitor.
When the FUNCTION switch (S3) is in the AM
position, +B is applied to the cathode of D1 via
R34. D1 will be cut-off and Q3 will turn off.
Q1 RF AMP. Q2 MIXER IFT
a
le
a@
Fig. 4-2 FM front end
IF Amplifier and Detector
This stage includes 2 dual-element ceramic fil-
ters, a transistor and an IC (PA3001-A) with a high
SN ratio and very little distortion. The transistor
inserted between the two ceramic filters is employ-
ed for impedance matching purposes as well as to
increase the gain.
PA3001-A includes the IF limiter amplifier, FM
detector (quadrature detector), AF amplifier,
muting circuit and the meter. drive circuit.
The muting circuit is turned on when pins 5 and
12 are connected by means of the FM MUTING
switch. If the dial pointer is moved approx.
+70kHz away from a station, and the input level is
very low (equivalent antenna input less than 4uV),
a 5V DC signal is generated at pin 12, and applied
to pin 5, thereby activating the muting circuit
within the IC.
FM MPX Stereo Demodulator
The IC (PA1001-A) employed in the FM multi-
plex stereo demodulator stage also features a high
SN: ratio and reduced distortion. Due to the in-
corporation of a pilot auto-canceller circuit, very
good frequency characteristics are obtained. Un-
like the more conventional pilot signal (19kHz)
canceller circuits, which fail to completely remove
the pilot signal if it is not at standard level,
PA1001-A pilot auto-canceller circuit also includes
a pilot signal level detector circuit. Changes in
pilot signal level are consequently responded to
immediately, resulting in very effective suppression
of the pilot signal leak level.
Filter Circuit
Besides eliminating the sub-carrier signals (more
than 23kHz), this PNP transistor 18dB/oct. active
filter also serves as an amplifier for the low-pass
region, and as a crosstalk canceller.

TX-6800
5. DISASSEMBLY
Side Panels and Top Panel
Remove the four screws (A), and remove the side
panels.
Bottom Plate
Remove the screw (B).
Front Panel
Pull off all the knobs, and remove the four screws
(C).
Top panel
Side panel
CG. 1n wAanmal
eo panel
Front panel
Bottom plate
n¢a—

6. PARTS LOCATION e The A mark found on some component parts indicates
the importance of the safety factor of the part. There-
fore, when replacing, be sure to use parts of identical
designation.
Front Panel View
Side
panel
L
Side
panel
R
AMS-033
AMS-034
Front
panel
ANB-721
Knob
(TUNING)
AAA-058
Knob (POWER,
FUNCTION,
FM
MUTING)
AAD-183
Front View
with
Panel
Removed
LED
(AM,
FM)
AEL-319
i
TUNING
Taytee
eieueree
LED
(STEREO)
AEL-315
A\Lever switch (POWER)
ASK-514
Tuning
shaft
assembly
AXA-228
Lever
switch
(FUNCTION)
Lever
switch
(FM
MUTING)
ASK-155
ASK-157
’ De-emphasis assembly
Top View GWS-188
Tuner assembly
Fuse
assembly
GWM-135
AWR-200
A Power transformer
ATT612
A\
Fuse
(1A)
Switch
assembiy
AEK-106
GWS-187
:
Lamp
(wedge
type)
Rear
Panel
View
AEL-029
Top
panel
Bar-antenna
AMS-035
ATB-505
Antenna holder
AXB-012
Terminal (OUTPUT)
AKB-062
A AC power cord
ADG-023
Terminal (ANTENNA) Slide switch (DE-EMPHASIS)
AKA-014 ASH-015

7.
DIAL
CORD
STRINGING
1.
Remove
the
wooden
case
and
front
panel
as
described
in
the
‘Disassembly’?
section
on
page
7.
Turn
the
tuning
capacitor
shaft
fully
clockwise.
Fix
the
tuning
drum
to
the
tuning
capacitor
shaft
so
that
the
set-screw
is
uppermost.
Tie
on
end
of
the
dial
cord
to
the
hook
on
the
tuning
drum.
Pass
the
cord
through
the
cut-out
section
in
the
tuning
drum,
and
then
take
it
over
pulleys
A,
B
and
C
in
that
sequence.
Wind
the
cord
around
the
tuning
shaft
2
times.
Pass
it
over
pulley
D,
wind
it
around
the
tuning
drum
2
times,
and
finally
tie
it
to
the
spring
hook
so
that
it
is tensioned.
Tuning drum
11.
12.
138.
TX-6GS00
Turn the tuning shaft, and check that the cord
moves smoothly.
Cut off any excess cord.
. Turn the tuning shaft counter-clockwise as far
as it will go.
Align the dial pointer with the starting point
of the dial scale (second division from the left),
and then pass the cord over it.
Check that the dial pointer is in line with the
starting point of the dial scale.
Finally apply the locking paint to the cord
securing positions (tuning drum hook and
spring hook) and the dial pointer connection.
Tuning shaft
VW AAA

8. ADJUSTMENTS
8.1 FM TUNER
e Connect the FM SG (FM signal generator) to
the FM ANTENNA 30002 terminals via a 3000
dummy antenna.
e Switch the FUNCTION selector to the FM
position, the FM MUTING switch to the OFF
position.
e The tuning coils in the FM front end dose not
have an adjusting core. Consequently, tracking
adjustments at 90OMHz are performed by regulating
the gap between rotor and stator of the tuning
capacitors (VC1, VC3 and VCs). The expression
“adjust VC (VC:i, VC3, VCs) found in the text
means that the two outer rotor blades of each of
these tuning capacitors are to be extended out-
wards with spatula (Part No. GGK-066) as shown
in Fig. 8-1.
Stator
Rotor blade | l
Stator
Rotor blade
~ Pd
A
Spatula > fL a
(GGK-066)
Fig. 8-1 Adjustment of tuning capacitor
1. Set the TX-6800 dial point to a frequency in
' the 106MHz region so that there will be no
input signal.
2.
Rotate
the
N
core
of
T2
to
bring
the
TUNING
meter
indicator
to
dead
center.
8. Next tune more accurately to 1O6MHz, and set
the FM SG output to 106MHz, 60 to 80dB
(modulation—400Hz, +75kHz deviation).
4. Adjust TCs to obtain maximum deflection of
the SIGNAL meter indicator, and a dead center
reading in the TUNING meter.
10
5. Then tune the dial pointer to 90MHz, and set
the FM SG output frequency to 90MHz.
6. Adjust the VCs to obtain maximum deflection
in the SIGNAL meter, and a dead center read-
ing in the TUNING meter.
7. Repeat steps 3 to 6 above.
8. Reset the FM SG output level to 20—30dB,
and adjust TC: and TCs at 106MHz, ‘and
VC: and VCs at 90MHz in the same manner
as described above in steps 3 to 7. These ad-
justments will ensure optimum sensitivity in
the 90 to 106MHz range, and minimum dif-
ference in sensitivity between the two extreme
frequencies.
9. Retum to a position with no input signal.
10. Rotate the N core of T2 again to set the
TUNING meter indicator to dead center.
11. Set the FM SG output to 98MHz and 66dB
(modulation—400Hz, +75kHz deviation), and
tune the TX-6800 to this position.
12. Then rotate the D core of Tz to reduce dis-
tortion in the demodulator output (OUTPUT
terminal) to a minimum.
18. Repeat steps 9 to 12 above until both specifi-
cations (center TUNING meter reading in the
absence of input signal, and minimum dis-
tortion in demodulator output) are satisfacto-
rily met.
Multiplex Decoder
e Connect the MPX SG (FM multiplex generator)
to the FM SG external modulator terminal.
e Set the FM MUTING switch to the ON position.
14. Set the FM SG output to 98MHz and 66dB
(unmodulated), and tune the TX-6800 to this
position.
15. Adjust VR: to obtain a 76kHz signal at TP .
terminal,
16. Then set the FM SG output level to 86dB, and
the modulation mode to external. Then with
the MPX SG, set Main to 1kHz, L+R to
+67.5kHz deviation, and pilot signal to
+7.5kHz deviation.
17. Rotate the T: core around by up to 90° in
either direction to reduce the demodulator
output (OUTPUT terminal) distortion to a
minimum,