Sansui 5900Z - Page 4

59002Z/4900Z/3900Z
2. OPERATION
2-1. General
1) Band Select Operation
By depressing the AM (0Se, f) or FM (oS4c, d) mode selector
switch, +B is supplied to flC, voltage reguiator and Pin No. 6 (fIC,)
for AM or Pin No. 5 for FM, and regulated power supply is fed to
fIC, electronic tuning controller.
2) Search Tuning Operation
When UP (fSg) or DOWN (fSg) search button is depressed, Pin No.
14 (f1C,) or Pin No. 15 (fIC;) is grounded. Then automatic search
circuit starts for Upper or Lower frequency, and tuning voitage
(voltage of variable capacitance diode) from Pin No. 10 (fiC,) in-
creases for UP or decreases for DOWN.
When a radio station signal came into the receiver and S-curve volt-
age from Pin No. 10 (dIC,} on FM or AM S-curve detector on AM is
fed to Pin No. 13 (fIC,) via fIC3), the radio station is tuned as pro-
cedure of Fig. 2-1.
In case of UP or DOWN button is kept depressed, the automatic
search Circuit continues its operation even when any radio station
signal came into the receiver.
3) Preset Tuning Operation
One of the preset channel buttons, i.e. channel (1) is depressed. Pin
No. 41 (fIC,) and sLD23 are grounded and kept shorting to ground
by fIC,.
Digital signal of the radio station memorized on channet (1) comes
out from 10 pins from Pin No. 25 to Pin No. 34, and converted to
analog voltage and fed to Pin No. 11 (fIC,}. f{C, starts Fetch action
and tunes the radio station memorized on channel (1) as procedure
of Fig, 2-2.
4) Preset Memory Operation
During the unit is receiving a radio station either AM or FM, the
digital signal converted from the tuning voltage appears on 10 pins
from Pin No. 25 to Pin No. 34 (fIC,). On this position, one of the
preset channel buttons is depressed when the memory button is
kept depressed, the digital signal is memorized with tuning band
mode on the depressed preset channel. (Previous preset station is
erased when this preset memory is operated.)
2-2. Priority of Functions
1} Tuning Function
SU oe ge ea ee oa UP search tuning
DIG hott ates Bie eed DOWN search tuning
OPO: wil ate alates Ss ae de Preset tuning
2) Band Selector
USO oe Gb eee See SD FM
CNG sos 4) oo. ee a ee AM
3) Preset Channel
First depressed channel has priority.
2:3. Automatic Tuning Compensation Operation.
1) Fetch Action (Refer to Fig. 2-2)
On the preset tuning, when the S-curve is out of detection by tuner
drift, the tuning voltage swings up to +8 steps (about +56 mV) as
preset voltage center. But in case of no S-curve detection caused
weak station signal, the tuning voltage returns to first preset voltage
after Fetch action.
2) AFC Operation (Refer to Fig. 2-1 and Fig. 2-2)
On the automatic search and the preset tuning, the S-curve voltage
fed to Pin No. 13 (fIC,) to control 10 bit up/down counter through
window comparator. The output of the counter is converted to
analog voltage by external ladder resistor and fed to Pin No. 11
(f1C;) and controls the tuning voltage for optimum reception.
On the other hand, PWM (Pulse Width Modulation) signal from Pin
No. 23 (fI1C,) is also converted to analog voltage and added to above
analog voltage for exact tuning.
4
2-4. Other Operations
1) Muting Operation
Pin No. 22 (f!C,) holds H level (about +8 V) during the automatic
search tuning, the preset tuning and the band seiect operations. This
H level is fed to Base termianis of dQ< and eQ3 (F-3318), and both
AM and FM audio signals are grounded through transistors.
2) Back Up Control Operation
When the mode selector is not AM or FM mode, or Power switch is
OFF, privious tuner reception frequency must be memorized. For
this memorization, Back Up Control Circuit applies to BUC terminal
Pin No. 3 (fIC,).
The back up control circuit is controlled by output voltage of Pin
No. 8 (f1C4) which is connected to Emitter terminal of fQg (F-
3326).
The output voltage of Pin No. 8 turns off faster than tuner B voltage
which is connected to Base terminal of fQg when the made selector
is switched from AM or FM mode to another mode, or the Power is
switched off. This means Collector terminal of fQg turns to L level
before the tuner B turns off. Then the back up circuit is actuated,
and the tuner reception frequency is memorized in the fIC,.
Fig.2-1 Search Tuning
Variable Capacitance
Diode Voltage
Muting
Muting ON —~—-—---__—__+ +
! OFF
1
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SL Level I |
SH Level
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i*—— Fine Tuning
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UP
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AFC
Operation
Speed t
Search High Speed Search
S-Curve Voltage Time
Fig.2-2 Preset Tuning
Variable Capacitance
Diode Voltage
Muting
an
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Muting ON ——-————_+ >
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SL Level
SH Level
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m—Fine Tuning
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Button ae V4 Delay
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AFC Ope, ation
Fetch Action( + 8step)
S-Curve Voitage Time