Pioneer QX-949A Series User manual

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Glx-g49A
CONTENTS
1.
2.
3.
4.
5.
6.
SPECIFICATIONS 3
5
I
FRONT PANEL FACILITIES ...
CONNECTION DIAGRAM
BLOCK DIAGRAM
LEVEL DIAGRAM
CIRCUIT DESCRIPTIONS
6.1 FM Tuner Section
6.2 AM Tuner Section
6.3 CD-4 Demodulator Section
6.4 SO Full Logic/RM Decoder Section
6.5 Control Amplifier
6.6 Power Amplifier Section
6.7 Protection Circuit
DISASSEMBLY
7.1 Wooden Gabinet
7.2 Bottom Plate .
7.3 Front Panel .
ADJUSTMENTS
8.1 AM Section
8.2 FM Section
9.3 FM MPX Section
C
8.4 Power Amplifier Section
DIAL CORD STRINGING
PARTS LOCATIONS
10.1 Front View 1
1O.2 Front View 2
10.3 TopView ...... 37
10.4 Bottom View. 39
10.5 Rear View 41
11. EXPLODED VIEWS 43
12. PACKING 52
13. SCHEMATIC DIAGRAMS, P.C. BOARD PATTERNS AND
PARTS LISTS
13.1 Schematic Diagrams and Miscellaneous Parts . 53
'13.2 TunerAssembly(AwE-041) .... 61
11
13
7.
8.
14
14
16
20
23
24
24
26
26
27
28
29
30
31
32
33
35
9.
10.

13.3 Headphone Jack Assembly (AWX-054) . . G7
13.4 Power Supply Circuit B Assembly (AWR-039) 68
13.5 CD-4Assembly(AWM-076) ...... 69
13.6 SO/RM Decoder Assembly (AWM-077) 77
13.7 ProtectionCircuitAssembly (AWM-079) ...... 83
13.8 Control Amplifier Assembly (AWG-023) 86
13.9 Power Supply Circuit A Assembly (AWR-080) 91
13.10 SwitchCircuitAssembly (AWS-048) ...... 94
13.11 Power Amplifier Assembly (AWH-027) gB
14. PARTS LIST OF EXPLODED VIEWS . . . . . .102
NOTE:
THE MODEL QX-949A COMES IN TWO VERSIONS DISTINGUISHED AS FOLLOWS:
Round label on
rear panel Voltage Type
F
KCU
110V, ]-20V,130V,220V,
and 240V (switchable)
120V only
General export model
UL (U.S.A.) and
CSA(Canada) approved

ABOUT 2CH POWER BOOSTING SWITCH
To increase available power when using the QX-949A for
2-channel reproduction, a convenient power select fea-
ture is incorporated. The covered compartment on the
rear panel houses a reversable connector panel. When
added power is desired during 2-channel operation tum
off set power. Open the cover, remove the connector
panel and rotate it 180o, then re-insert it and close the
cover. Be sure to reverse the connector again before
retuming to 4-channel operation.
These illustrations show how the boosting switch is employed.
:1 J
Pull out connector Rotate connector 180" and re-insert it
Loosen screw to open cover
CHANGING LINE VOLTAGE SETTING AND FUSE
(F MODEL)
To remove the fuse, unscrew the fuse cap located in the
center of the line voltage selector and withdraw it,
together with the fuse. Next, pull the line voltage
selector plug out of its socket, rotate it until the
cutaway aligns with the appropriate line voltage marked
on the back of the unit, then push it back into its socket.
It is important to check the rating of the fuse; a 3A
fuse should be used with either 220Y or 240V, while a
6.4 fuse should be used for 110V, 720V, or 130V
operation. If the fuse rating is correct, reinsert it and
screw in the fuse cap.
No selector plug is provided for "KCU" type (120V only
model).
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5. LEVEL DIAGRAM
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6. CIRCUIT DESCRIPTIONS
6.1 FM TUNER SECTION
Front End
This consists of. a 4-gang variable capacitor tuning
circuit, dual-gate MOS FET RF amplifier and
mixer, and local oscillator with buffer. By employ-
ing a glounded gate-Z of the dual-gate MOS FpT,
the circuit becomes equivalent to a cascade ampli-
fier, providing large gain with stable operation in
the RF amplifier.
In the mixer stage, the signal is applied from the
local oscillator to gate-2. This method allows input
power from the local oscillator to be minimized
and features low mutual interference. A variation
of a Clapp circuit forms the local oscillator and by
inserting a buffer amplifier between it and the
mixer, the oscillator load is reduced and waveform
distortion suppressed. The oscillation frequency
drawing effect is also eliminated, to provide
extremely stable operation even with strong inputs.
lF Amplifier and Detector
These are composed of three dual-element ceramic
filters and two integrated circuits. The first stage
IC (HA1201") incorporates a current limiter, while
the second stage IC (HA1137) is shown in Fig. 2.
When pin 12 of HA1137 is at more than xTOkHz
detuning and with an extremely low input level,
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a DC voltage is produced. By setting the FM
Muting switch to ON, pin 12 is connected to pin
5, and the analog switch in HA1137 is operated
ON-OFF to perform muting.
Multiplex Decoder
Demodulation is performed by switching detection
with the circuit contained in the IC (HA1156),
depicted in Fig. 3. A phase locked loop (PLL)
produces a 38kHz square wave synchronized to
the pilot signal. The two gates are alternately
switched ON-OFF by this signal to derive the L
and R channels from the composite signal. By
detecting the pilot signal level, the switching signal
from PLL to demodulator is operated ON-OFF.
The STEREO indicator lights at the same time.
6.2 AM TUNER SECTION
This consists of a 3-gang variable capacitor tuning
circuit, a dual element ceramic filter and an IC
(HA1138). The IC (Fig. 4) contains an RF stage
and two IF amplifier stages.
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