Sansui T77 Service Manual

Page 2

<> BLOCK DIAGRAM

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IM/FM (TIITZ)
L
1. OPERATION
1-1. General 1-2. Operation of quartz PLL synthesizer circuit
The main functions of the Quartz Synthesizer Tuner T-77 will be Fig-1'1 PLL Synthesizer bIOCk diagram
described below: RF
1 M l . f h 875 »meouuz(mi M e, IoliIEzILMI
) anua tuning 0 one step/one pus . Powwow Ix 460kHz(AM)
If UP or DOWN key switch is pushed once lightly, the receive fre- f
quency (every frequency displayed on the indicator tubes) changes Egg * W v ignorant/{fling
by one step (100 kHz in FM; 1 kHz in AM). ass-"W
2) Fast forwarding tuning E G-IIUIIZ
. . . . A l D -u , ,7 7v
While UP or DOWN key swuch is kept pushed slightly, the receive g 5 5 1 LRefiirfncelreq,
- I T: - ____________________
frequency continues to change. E g f I I 12??sz 1,
. . E . k
3) Automatic search tuning T § : 5:;ser5nc1a $223522: / z I
If UP or DOWN key switch is pushed once deeply, the receive fre- g 3:? : mm a" :
quency continues to change and stops when it reaches a frequency 1 :
of the next broadcasting station. Prescaler : P'Ofi'amwjfie 60"6' ~- Phase :
4) Memory write and memory read 'F MW" " mm / I IZSSEZéAZEEml l25kHZ(FM) :2?" I LPF
By pushing MEMORY and STATION key switches, it is possible to I : Nzntlonm) WW I
store the receive frequencies of six FM/AM stations. And also, by / I N'Mwuw J'
- . . . , L ______________________
pushing one of STATION key swnches once, it IS pOSSlbIe to select 12275-145375MHzirM) iPresetlnDUI
. . . 985 ~2oesmz(w) I "=3751°3°(FM)
any desired station automatically. 1n=525 ~1605(AM)
. . . . K t b d
5) Digital display of receive frequency mfiflnfilliméwcmo -- (5392:3303: :ar'eceive
The receive frequency is displayed digitally by using fluorescent "mum
indicator tubes. Fig. 1-1 shows a PLL circuit for stabilizing the local oscillator fre-
The Quartz Synthesizer Tuner T-77 comprises a PLL synthesizer quencies.

circuit (TC 9123P) for mainly stabilizing the local oscillator fre-
quencies, a synthesizer control circuit (TC 9124AP), a digital display
circuit (TC 502QBP) for displaying receive frequencies, and a muting
control circuit.

The local oscillator frequency fed from a VCO local oscillator is
divided by a Pre-Scaler section, and further divided by a program-
mable counter section (a counter by which a divide ratio N can be
predetermined freely by presetting it from outside) into l/N.

Page 6

2) When AM is received (See Fig. 1-8)

In the case where AM is received in the automatic search tuning, the
muting operates in the same way as in the case where FM is re-
ceived.

If the search operation begins, the AM/IF amplifier (fog and f0)
comes into operation. The output of the AM/IF amplifier is con-
nected to Pin 8 of NOR-3 and is usually kept at H level. Also, since
Pin 5 of NOR-2 is at H level in AM, Pin I of NOR-I is fixed at L
level. Since Pin 2 of NOR~1 is at H level during scanning operation,
Pin 9 of NOR-3 is at L level.

If a frequency of a broadcasting station is received, the AM wave is
amplified by ng and le3 and is then applied to Pin 8 of NOR-3.
As a result, when it reaches a threshold level of Pin 8 of NOR-3,
Pin 10 changes as shown in Fig. l-9 and this output turnsz ON
through a narrow.band ceramic filter.

This narrow-band ceramic filter is used to prevent error operation
due to noise in the automatic search. As a result, Pin 12 of NOR-4
changes to L level, At this time, if the signal indicator level exceeds
two, f0, is turned ON to change Pin 13 of NOR-4 to L level and
Pin I I to H level. The signal of Pin 11 is an AUTO/STOP control
signal for the control IC of TC 9124AP; therefore, the automatic
searCh operation stops. As a result, the pulse generated at Pin LD-
out of the PLL synthesizer IC TC 9123p is stopped to change Pin
2 of NOR-I to L level and Pin 3 to H level, and thus the muting
operation is released. In the case of manual tuning, the muting
operates for a moment when the UP/DOWN key switch is depressed,
in the same way as in the case of the manual tuning in FM MONO,

Fig. 1-8 AM Muting control circuit

m Tuna-r IC

'C' "197 Meier OUT

I5'-*

9
IF OUT

lama Lock~®ms
Unlock "I, 15
L0 OUT

IE2 rcstzsP

IOI2

IOn

" '-" LCHOv'
-6;

i

-OP CH OUT
60:»!

Till

0C 3 TCSIZIIP

A- STOP
I12

gontrul '0
Fig. 1-9

LBMIG
a

' | l
.-

NOR3 Pin 8
Input Signal

NOR 3 Pm 10
Output Signal

H. Level

L Level

2. INTERIOR BLOCK DIAGRAM OF IC

4. HA1197 (AM tuner IC)

1. uPC 1161 (MPX Decorder IC)

llfil I15 IUI ll3l IIZI llll IIOI 9|
PLOT smite
vco, ms: LOCK mm: 5 Tc
76 DETECTOR 0:1:ch LYWBMVER
i l I *
si-msw 76m: to m: to saw 10
P VLO STOP 38m I9lflz lkiz
94 mm owner: cum:
I L-Ol
[-i- I I I" P051 Aw
STEREO
PRU"? "FM Whoa H.
I__l 905nm
-1 l-""-
Ill [2II3II4II5116II7II8I

2. LA-123'I (IF amp & FM detector IC)
l1 s 9 l0

I Voltage Regulator I Quadrature V
LImItIer
IF Amp/Liming: f fife/(Tune _7
1-*1st 2nd am am 5th 6th t Quadrature Um
I #- Detector
3_ Audio 6
Amp
I Level Level Level imer- Level IX: Level _ _ _ _
4 De! Der, Der, ter Bet Bet mm __5
Mute
lF Amp Signal Meter Mute
Mite Drive Drive fl
. l l
15 13 16 12 H
3. MSM4001RS (NOR1 ~ 4)
VDD

14 13 II 10 9 8
I 112 l I

w <93

II

SUB

IFA-S

AGC DRlV

é)

" SM WIVI

5. LB-1416 (Signal LED drive IC)

Vcc Vref R02
8 5 4

6. MSM4011 RS (NAND 1 ~ 4)

VDD

O 8
I I

no

141312111
I I I I

D

GND