Pioneer SX-303/S Instrukcja serwisowa - Strona 6
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5. CIRCUIT
DESCRIPTIONS
FM Front End
A
unitized
variable
capacitor
type
front end
unit 1s used consisting of an FET RF single stage
amp,
local
oscillator/mixer
IC and an IF trans-
former.
FM IF Amp, Detector and MPX Circuit
A 2-transistor IF amp with ceramic filter is used
and the next stage has an IC (M51533L) contain-
ing the FM IF detector and MPX circuit. The block
diagram of IC M51588L is shown in Fig. 5-1. This
IC uses a peak detection
method
which
can
be
adjusted with a single coil. The PLL method is
employed
to reconstitute
the 38kHz
sub-carrier
for the MPX circuit.
The IF signal is input at pin 1 and the detection
output is obtained from pin 5. The detection out-
put passes through the muting Q4, goes to pin 9,
passes through the MPX circuit and the stereo
signals
are
obtained
from
pins
11
and
12. In
addition, this unit detects the presence or absence
TUNING
y)
|
Z
T.P 6
TP |
a t
©
m s
3rd
1F
AM
oO
FM
S1-3
f
ai
L OUT
Fig. 5-1
paar,
f
(6)
PHASE
\/2
\/2
ile
Shan
COMPARATOR|
|
"°°
DIVIDER
DIVIDER
1
!
nes
L
LEVEL
INPUT
@)
alae
BUFFER
CIRCUIT
STEREO
(13)
: SWITCH
Fiancee
J
IND
7
MPX
On
of a pilot signal to automatically switch between
stereo and mono
reception by R14 which is con-
nected to pin 14. When a stereo signal is received,
—
pin 13 drops to the low level to light the stereo
indicator. When pin 2 is grounded, the PLL VCO
and FM IF operation stop (for AM).
FM Muting and LED Driver
A
RI4
LL]
M5i533L
(10)
:
+B2
1/2
STEREO
PHASE
FM 1F, Detector and MPX circuit