Sansui 5900 Z Service Manual

Page 4

SEOUZKQBODZ/CJJOOZ

2. OPERATION

2-1 . General

1) Band Select Operation

8y depressing the AM (053e, f) or FM (asac, d) mode selector
switch, +8 is supplied to "C; voltage regulator and Pin No. 6 lth.)
for AM or Pin No. 5 for F M, and regulated power supply is fed to
flCl electronic tuning controller.

2) Search Tuning Operation
When UP (69) or DOWN US.) search button is depressed, Pin No.

14 (nc,) or Pin No. is VIC.) is grounded. Then automatic search
circuit starts for Upper or Lower frequency, and tuning voltage

(voltage of variable capacitance diode) tram Pin No. 10 ("(1) 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 (dlCl) on PM or AM S-curve detector on AM is
led to Pin No. 13 ((21) via flC3). 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, Le. channel (1) is depressed. Pin
No. 4i ((2) and sLDu are grounded and kept shorting to ground
by rtc..

Digital signal of the radio station memorized on channel (1) comes
out from 10 pins from Pin No. 25 to Pin No. 34.and converted to
analog voltage and fed to Pin No. )1 mcu. llC( 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 (rig). On this position,one of the
preset channel buttons is depressed when the memory button is
ltept 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

lst ........... UP search tuning
2nd ........... DOWN search tuning
3rd ........... Preset tuning

2) Band Selector
1st FM
2nd ........... AM

3) Preset Channel

First depressed channel has priority.

23. 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. Out 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)

09 the automatic search and the preset tuning, the S~curve voltage
fed to Pin No. 13 (flcl) to control 10 bit up/down counter through
wildow comparator. The output of the counter is converted to
analog voltage by external ladder resistor and fed to Pin No. )1
(fig) and controls the tuning voltage for optimum reception.

On the other hand, PWM (Pulse Width Modulation) signal from Pin
No. 23 UK.) is also converted to analog voltage and added to above
analog voltage (or exact tuning.

4

2-4. Other Operations

1) Mating Operation

Pin No. 22 NC.) holds H level (about #8 V) during the automatic
search tuning, the preset tuning and the band select operations. This
H level is fed to Base termianls of do; and co; (F3318). 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 (flC. ).

The back up control circuit is controlled by output voltage of Pin
No. 8 (flCz) which is connected to Emitter terminal of .09 (F-
3326).

The output voltage 0! Pin No. 8 turns off fasrer than tuner 8 voltage
which is connected to Base terminal of fog when the mode selector
is switched from AM or FM mode to another mode, or the Power is
switched off. This means Collector terminal of fog turns to L level
before the tuner 8 turns off. Then the back up circuit is actuated.
and the tuner reception frequency is memorized in the HQ.

Fig.2-i Search Tuning
Variable Capacitance
Diode Voltage
I
cu-.- Mining ON -.. ---- M3229

u-.;:'~a".o- 9-..; ---

.
t
t
I
I
I
I
I
I
r
d
I
t

.- Fine Turing

---~-~

/
UP Button"> W AFC Operation

32"
arch High Speed Search
C O

S-Curve Voltage Time

Fig.2-2 Preset Tuning

Variable Capacitance
Diode Volteoe
a

:"'

ll-OO-Oluyiuob-Ioun-ne
o f
.g
C

I I
l I
I
I I
l I
I I
I I
I I
: I
: i "'"I
- l
(3an [IEOW'T' - 7;
I ; 1 ; AFC Operation
. Fetch Act-om - Est-oi
4.
S-Curve Voltage Time