Sony ICF-C793, ICF-C793L Service Manual

ICF-C793/C793L

SERVICE MANUAL

Ver 1.0 1999. 02

Photo: ICF-C793L

SPECIFICATIONS

US Model

Canadian Model

Australian Model

ICF-C793

AEP Model

ICF-C793/C793L

UK Model

ICF-C793L

MICROFILM

ICF-C793

FM/AM PLL SYNTHESIZED CLOCK RADIO

ICF-C793L

FM/MW/LW PLL SYNTHESIZED CLOCK RADIO

TABLE OF CONTENTS

2

1. GENERAL ................................................................... 3

2. DISASSEMBLY ......................................................... 5

3. ELECTRICAL ADJUSTMENTS......................... 6

4. DIAGRAMS

4-1. Block Diagram ................................................................ 9

4-2. Printed Wiring Boards .................................................... 11

4-3. Schematic Diagram ......................................................... 13

4-4. IC Pin Function Description ........................................... 16

5. EXPLODED VIEWS................................................ 17

6. ELECTRICAL PARTS LIST ............................... 19

SAFETY CHECK-OUT

After correcting the original service problem, perform the follow­ing safety check before releasing the set to the customer:
Check the antenna terminals, metal trim, “metallized” knobs,
screws, and all other exposed metal parts for AC leakage.
Check leakage as described below.

LEAKAGE TEST

The AC leakage from any exposed metal part to earth ground and
from all exposed metal parts to any exposed metal part having a
return to chassis, must not exceed 0.5 mA (500 microampers.).
Leakage current can be measured by any one of three methods.

1. A commercial leakage tester , such as the Simpson 229 or RCA
WT -540A. Follo w the manufacturers’ instructions to use these
instruments.

2. A battery-operated AC milliammeter. The Data Precision 245
digital multimeter is suitable for this job.

3. Measuring the voltage drop across a resistor by means of a
VOM or battery-operated AC voltmeter. The “limit” indica­tion is 0.75 V, so analog meters must have an accurate low­voltage scale. The Simpson 250 and Sanwa SH-63Trd are ex­amples of a passive VOM that is suitable. Nearly all battery
operated digital multimeters that have a 2 V A C range are suit­able. (See Fig. A)

To Exposed Metal
Parts on Set

Notes on chip component replacement

• Never reuse a disconnected chip component.

• Notice that the minus side of a tantalum capacitor may be dam­aged by heat.

SAFETY-RELATED COMPONENT WARNING!!

COMPONENTS IDENTIFIED BY MARK ! OR DOTTED
LINE WITH MARK ! ON THE SCHEMATIC DIAGRAMS
AND IN THE PARTS LIST ARE CRITICAL TO SAFE
OPERATION. REPLACE THESE COMPONENTS WITH
SONY PARTS WHOSE PART NUMBERS APPEAR AS
SHOWN IN THIS MANU AL OR IN SUPPLEMENTS PUB­LISHED BY SONY.

AC

1.5 k

0.15 µF

Fig. A. Using an AC voltmeter to check AC leakage.

Ω

Earth Ground

voltmeter
(0.75 V)

HOW TO CHANGED THE CERAMIC FILTERS

This model is used two ceramic filters of CF2 and CF3.
You must used same type of color marked ceramic filters in order
to meet same specifications.
Therefore, the ceramic filter must changed two pieces together
since it’s supply two pieces in one package as a spare parts.

Mark Center frequency

CF

mark

red 10.70 MHz

blue 10.67 MHz

ATTENTION AU COMPOSANT AYANT RAPPORT

LES COMPOSANTS IDENTIFIÉS P AR UNE MARQUE !
SUR LES DIAGRAMMES SCHÉMATIQUES ET LA LISTE
DES PIÈCES SONT CRITIQUES POUR LA SÉCURITÉ
DE FONCTIONNEMENT. NE REMPLACER CES COM­POSANTS QUE PAR DES PIÈCES SONY DONT LES
NUMÉROS SONT DONNÉS DANS CE MANUEL OU
DANS LES SUPPLÉMENTS PUBLIÉS PAR SONY.

À LA SÉCURITÉ!

– 2 –

CF3

orange 10.73 MHz

black 10.64 MHz

white 10.76 MHz

LOCATION OF CONTROLS

SECTION 1

GENERAL

This section is extracted from
instruction manual.

– 3 –

– 4 –

SECTION 2

)

t

DISASSEMBLY

Note: Follow the disassembly procedure in the numerical order given.

CHASSIS ASS’Y

7

chassis assy

5

Break the soldering of
speaker lead.

6

button (DST)

2

claw

4

connector
(CN301)

3

rear cabinet

1

four screws (P3 × 14

2

three claws

POWER CORD SETTING

Set the power cord as illustrated below,
then install the cabinet.

Put the secondary flat cable
between bosses to fix.

power cord

1

screw (P3 × 14)

6

knob (brightness)

rear cabine

boss

rear cabinet

power cord

– 5 –

SECTION 3

r

ELECTRICAL ADJUSTMENTS

0 dB = 1 µV

[FM]

Setting:

Band switch: FM

FM RF signal

generator

22.5 kHz frequency
deviation by 400 Hz
signal
Output level: as low as possible

[AM (MW/LW)*]
*AM : ICF-C793

MW/LW: ICF-C793L

Setting:

Band switch: AM (MW/LW)

AM RF signal

generator

30% amplitude
modulation by
400 Hz signal
Output level: as low as possible

Put the lead-wire
antenna close to
the set.

FM antenna in

0.01 µF

set

MAIN board
TP (SP +)

level meter

8

Ω

set

MAIN board TP (SP GND)

MAIN board
TP (SP +)

level meter

8

Ω

+
–

MAIN board TP (SP GND)

FM VCO VOLTAGE ADJUSTMENT

Adjustment Part Frequency Display Reading on Digital Voltmeter

L4 87.5 MHz 3 V ± 0.1V

Confirmation 108 MHz Less than 11.8 V

FM TRACKING ADJUSTMENT

Adjust for a maximum reading on level meter.

+
–

Adjustment Part Frequency Display Reading on Digital Voltmeter

Confirmation

Adjustment Part Frequency Display Reading on Digital Voltmeter

Confirmation 279 kHz Less than 9.5 V

L3 87.5 MHz

TC3 108 MHz

AM (MW) VCO VOLTAGE ADJUSTMENT

L5 530 kHz (531kHz *1) 2.65 V ± 0.1V

1,710 kHz

(1,602 kHz *1)

AM (MW) TRACKING ADJUSTMENT

Adjust for a maximum reading on level meter.

L1 (L1-1 *2) 580 kHz (621 kHz *1)

TC1 1,490 kHz (1,404 kHz *1)

LW VCO V OLTAGE ADJUSTMENT *2

TC4 153 kHz 2.25 V ± 0.05V

Less than 10 V (9.5 V *1)

• Repeat the procedures in each adjustment several times, and the
frequency coverage and tracking adjustments should be finally
done by the trimmer capacitors.

• Remove FM antenna in FM adjustments.

digital voltmete

MAIN board

TP (VT)

+
–

Adjustment Location: Main Board (See page 7)

LW TRA CKING ADJUSTMENT *2

Adjust for a maximum reading on level meter.

L1-2 162 kHz

TC2 243 kHz

AM IF ADJUSTMENT

Adjust for a maximum reading on level meter.

T1 450 kHz

*1) Except US, Canadian models
*2) -ICF-C793L

– 6 –

TC2 L1-2 L1 (L1-1*)

AM (MW) Tracking Adjustment

LW Tracking Adjustment

*

L3 TC3

FM T rac king Adjustment

T1 AM IF

TC1 AM (MW) Tracking Adjustment

L4 FM VCO Voltage Adjustment

L5 AM (MW) VCO Voltage Adjustment

TC4 LW VCO V oltage Adjustment

*

TP (VT)

TP (SP+)

TP (SP GND)

TP (FM-IN)

– MAIN BOARD (Component Side) – – MAIN BOARD (Conductor Side) –

Adjustment Location:

*) ICF-C793L

– 7 –

SECTION 4

DIAGRAMS

ICF-C793/C793L

4-1. BLOCK DIAGRAM

ANT1

FM LEAD

ANTENNA

(C793)

L1

L1-1

(MW)

(C793L)

AM (MW/LW)
FERRITE-ROD

ANTENNA

L1-2

(LW)

LW TRACKING

L1-2, TC2

TC2

L1, TC1

AM TRACKING

Q1

MW/LW

SWITCH

D1-2

B.P.F.

BPF1

(C793L)

L1-1, TC1

MW TRACKING

TC1

FM TRACKING

L3

FM RF

(C793)

D4-1
D1-1

(C793L)

L3, TC3

D2

AM (MW) VCO VOLTAGE

L5

AM (MW/LW)

OSC

LW VCO

VOLTAGE

(C793L)

TC4

MW/LW
SWITCH

• SIGNAL PATH

TC3

9

FM

FM RF
IN

12

AM RF
IN

10

L5

TC4

Q3

RF

FM

FRONT-END

AM

FRONT-END

AM OSC

5 7

(C793)

(C793L)

D4-2
D1-3

FM/AM
FE OUT

14 17

+

AM IF

FM OSC

L4

FM VCO VOLTAGE

L4

FM OSC

D3

(C793L)

CF2

10.7MHz

CF3

10.7MHz

T1

CF1

450kHz

2

16

FM/AM FRONT-END,

FM/AM IF AMP, DET, AGC, AF AMP

FM
IF IN

FM
DISCRI

AM
IF IN

FM/AM

BAND

SELECT

15

IC1

FM

IF AMP

FM

DISCRIMINATOR

AM IF AMP,

AGC, DET

TUNING METER

19

METER

DET
OUT

23

+

(C793L)

Q5

TONE

CONTROL

SWITCH

24

AF
IN

POWER AMP

AF

NF

3 4

VOL

MUTING

Q4

OUT

AF

27

VR1
VOL

: FM
: AM (MW/LW)

SP301

(SPEAKER)

D74

LOW-PASS FILTER

Q50, 51

15

XOUT

X50

75kHz

05

1

2

XIN

X1

22 23

4.19MHz

X101

PD1

X2

5

27

XT1

19 20

X100

32.768kHz

DA

4

26

DATA

XT2

CK

CLK

FM/AM PLL

CE

3

34

CE

IC50

S0 – S23

60 – 37

LIQUID CRYSTAL DISPLAY

LCD100

11

12

AM IN

COM0 – COM3

61 – 64

FM IN

P1

KS0 – KS4
10 – 13, 8

S101, 201 – 218

(KEY MATRIX)

78

P0

Q52
MW/LW
SWITCH

CONTROL

B+

SYSTEM CONTROLLER,

LCD DRIVER, KEY CONTROL

IC100

KR0 – KR3

14 – 17

A RADIO

(LCD BACK LIGHT)

D74 D75

6

(SYSTEM CONTROLLER IC100 B+)

LED DRIVE

Q53, 54

ALM A

18

BACKUP B+

D75

B BUZZER

7

ALM B

RESET

D70 – 73

(LCD BACK LIGHT)

RESET SIGNAL

GENERATOR

IC101

S50

BRIGHTNESS

D60, 61

–2

–1

D100

VT B+

B+

HIGH

LOW

D102

35

36

33

MUTE

BUZZER

BZ-CTRL

PDET

28

D101

T301

POWER

TRANSFORMER

B+

REGULATOR

Q57

RECT

D351 – 354

RECT
D355

AC IN

– 9 – – 10 –

4-3. SCHEMATIC DIAGRAM

• IC Block Diagrams
– MAIN BOARD –

IC1 CXA1019M

FM/AM

IF OUT

14 13

FE GND

FM RF IN

12

FM IF

NC

11

AM RF IN

FM RF

10 9 8 7 2 16 5 34

TUNING METER

FM OSC

REG OUT

FM FE

FM

DISCRIMINATOR

AM FE

AM IF DET AGC

AFC

AM OSCNFVOL

AF POWER AMP

FM DISCRI

ICF-C793/C793L

GND

• Waveforms
– MAIN BOARD –

1 IC50 2 (X IN)

1 V/DIV, 10 µs/DIV

15

SELECT

FM/AM BAND

16

AM IF IN

17

FM IF IN

IC50 BU2614FS

PD1

VSS

16 12131415

PHASE

DETECT

XOUT

2 IC100 !ª (XT1)

1 V/DIV, 20 µs/DIV

3 IC100 @™ (X1)

1 V/DIV, 500 ms/DIV

XIN

30.5 µs

18

19

NC

VDD2

VDD1

MAIN CONTROL

PRESCALLER

I/O CONTROL

REGISTER

5

4

CE

CK

METER

DA

20

IF GND

FM IN

11

61 2 3 7

CD

2 Vp-p

21

AFC AGC

AM IN

10

OUTPUT

CONTROL

P0

P2

8

P1

22

AFC AGC

IF-IN

9

IF

COUNTER

23

DET OUT

24

AF IN

26

25

RIPPLE FILTER

VCC

28

27

GND

AF OUT

Note on Schematic Diagram:

• All capacitors are in µF unless otherwise noted. pF: µµF
50 WV or less are not indicated except for electrolytics
and tantalums.

• All resistors are in Ω and 1/
specified.

¢

•

: internal component.

4

W or less unless otherwise

• C : panel designation.

Note:

The components identi­fied by mark ! or dotted
line with mark ! are criti­cal for safety.
Replace only with part
number specified.

Note:

Les composants identifiés par
une marque ! sont critiques
pour la sécurité.
Ne les remplacer que par une
piéce portant le numéro
spécifié.

• U : B+ Line.

• H : adjustment for repair.

• Voltages and waveforms are dc with respect to ground
under no-signal (detuned) conditions.
no mark : FM
( ) : AM (MW/LW)

• V oltages are taken with a VOM (Input impedance 10 MΩ).
Voltage variations may be noted due to normal produc­tion tolerances.

• Waveforms are taken with a oscilloscope.
Voltage variations may be noted due to normal produc­tion tolerances.

• Circled numbers refer to waveforms.

• Signal path.

F : FM
f : AM (MW/LW)

• Abbreviation
AUS : Australian model
CND : Canadian model
FR : French model

– 13 –

– 14 –

13.3 µs

1.9 Vp-p

238.7 ns

2 Vp-p

Note:

• Press either [+] or [–] key when RADIO is being
operated, oscillation will be given out for 250 ms.

• Oscillation will be given out for 250 ms when the
power is turned on.

– 15 –