Fm Tuner Section; Am Tuner Section; If Amplifier And Detector; Multiplex Decoder - Pioneer sx-d5000 Service Manual

3. Memory
o A total of 6 FM frequencies and 6 AM fre-
quencies may be stored in the memory.
o Also auto memory of the previous tuned fre-
quency when switching back and forth between
FM and AM bands.
o Last-one memory (the last frequency tuned
when the power is switched off will be auto-
matically retuned when the power is switched
back on).
o Memory maintained by a separate power supply
when the main power is switched off (i.e. when
the POWER switch is turned to STAND BY
position).
. Memory also maintained (for 3 to 4 days) when
the power is turned off completely (i.e. when
power cord is disconnected or a power failure
occurs).
4. Indicators
o The received frequency is displayed in digital
form by fluorescent indicator tube.
o Signal strength is indicated by the SIGNAL
indicator composed of fluorescent indicator
tube 5-point indicator display.
o Tuning indicator.
o Memory read-out indicator.
o Memory write-in indicator.
o FM STEREO indicator.
4 . 2 F M T U N E R S E C T I O N
Front-End
The FM front-end includes a dual-gate MOS
FET RF amplifier (single stage) and a variable
capacitance diode corresponding to a 4-ganged
tuning capacitor. The local oscillator signal is
applied to the synthesizer circuit for comparison
with a reference signal, the resultant tuning voltage
then being applied to variable capacitance diode
for
determination
of the oscillator frequency
(i.e. tuning frequency).
lF Amplifier and Detector
These employ 3 ICs and 3 dual-element ceramic
filters. The IC (HA1201) of the first 2 stage
constitutes
a single-stage differential
amplifier
current-limiting limiter. The IC (PA3007-A) in
the third stage, an improvement on the former IF
system IC (PA3001-A), includes an IF limiter
amplifier, quadrature detector, meter drive, and
other circuits. Performance in terms of distortion,
S-N ratio, delay characteristics, and other para-
meters, shows a marked improvement in com-
parison to the PA3001-A.
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 fur-
ther improved by incorporating a chopper type
MPX decoder. The chopper type switching circuit
operates by switching the signal either to ground or
to the through circuit, thereby eliminating the
generation of unwanted noise or distortion. Fur-
thermore, since the PA4006-A features DC direct-
coupled switching with the detector, there is no
deterioration in separation at the low frequency
end.
Besides the decoder and muting circuits, the
PA4006-A also incorporates the pilot
signal
canceller, stereo auto selector, VCO killer circuit,
muting amplifier, and muting control circuit.
De-emphasis involves the use of the audio
amplifier NFB circuit, while the muting gate is
opened and closed according to the various muting
signals from the internal control circuit and other
external circuits.
4 . 3 A M T U N E R S E C T I O N
See Fig. 4-1 for an outline of the AM tuner IC
(HA1138). The tuning circuit employs a variable
capacitance diode (vari-cap) which corresponds to
a 2-ganged tuning capacitor. The local oscillator
signal is compared with a reference signal in the
synthesizer circuit, and the resultant tuning fre-
quency then applied to the vari-cap for determina-
tion of the oscillator frequency (tuning frequency).
And in order to improve performance with strong
input signals, the IC has been equipped with an
AGC (automatic gain control) circuit, and the bar-
antenna fitted with a. damping coil. The AGC
varies the damping current by means of an FET
according to the RF amplifier output level.
AM STEREO
O U T
TO TUNING DETECTOR
I O S Y N T H E S I Z E R
C I R C U I T
B A R -
T U N I N G
ANTENNA
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A M T U N E R I C { H A i I 3 8 )
F i g . 4 - 1 A M T u n e r C i r c u i t