Sony ST JX421 Service Manual

Page 2

ST-JX421/JX521

SAFETY CHECK~OUT TABLE OF CONTENTS
32mm title Rage
After correcting the original service problem,
perform the following safety check before releasing Specification ..........

the set to the customer:
Check the antenna terminals, metal trim, metallized

Safety Check-out

knobs, screws, and all other exposed metal parts for 1_ GENERAL
AC leakage. Check leakage as described below. 1-1. Location of Controls
1-2. Connections ~~~~~~~~~~~~~~~~~
LEAKAGE TEST
2. ELECTRICAL ADJUSTMENTS """""""""""""" 6
The AC leakage from any exposed metal part to
earth ground and from all exposed metal parts to any 3. DIAGRAMS
exposed metal part having a return to chassis, must 31 Printed Wiring Boards ......................................... 7
01 exceed 05 mA (500 microampers). Leakage 32. Schematic Diagrams (Tuner Section) N 11
cum can b9 measured by any one Of three 8-3. Semiconductor Lead Layouts ~~~~~~~~~~~~~~ 13
methods. 34 Wavefoms ........................................................ 13
I. A commercial leakage tester, such as the 3'5 Schematic Diagram
Simpson 229 or RCA WT-SAOA. Follow the (Control and Power Seam) """ 14
manufacturers instructions to use these instru-
ments. 4. EXPLODED VIEW ............................................... 17
2. A battery-operated AC milliammeter. The Data 6. ELECTRICAL PARTS LIST ................................ 19

Precision 245 digital multimeter is suitable for
this job.

3. Measming the voltage drop across a resistor by
means of a VOM or batterycperated AC volt-
meter. The limit" indication is 0.7SV, so
analog meters must have an accurate low-
voltage scale The Simpson 250 and Sanwa
SH-63Trd are examples of a passive VOM that

To change the AM tuning interval

The AM tuning interval is preset at the factory to 10 kHz
to match the frequency allocation system of your
country. To change the interval to 9 kHz, proceed as
follows.

1 Depress the POWER switch to turn on the unit.

2 Set the BAND FM/AM selectorto AM.

3 Press the POWER switch to turn off the unit.

4 Hold the TUNlNG knob in the + " position. and
depress the POWER switch to turn on the unit.
To reset the interval to 10 kHz, tollow the same
procedure.

is suitable. Nearly all battery operated digital
multimeters that have 3 2V AC range are
suitable. (See Fig. A)

Ta Exposed Metal
Part: on Set

AC
|: $1.5 ktl / voltmeter

(0t 75 V}
'._J

'5? Earth Ground

Note

When the interval is changed. all preset stations which
you have memorized using the numeric buttons will be
erased from the memory. Alter changing the interval, be
sure to preset the stations again,

0.15uF

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

SAFETY-RELATED COMPONENT WARNING
COMPONENTS IDENTIFIED BV MARK A OR DOTTED

ATTENTION AU composmr AVANT RAPPORT
A LA SECURITEI

LINE WITH MARK A 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 MANUAL OR IN SUPPLEMENTS PUB-
LISHED 8V SONY.

LES COMPOSANTS IDENTIFIES PAR UNE MAROUE A
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DE FONCTIONNEMENT. NE REMPLACER CES COM-
POSANTS QUE PAR DES PIECES SONV DONT LES
NUMEROS SONr DONNES DANS cs MANUEL ou
DANS LES SUPPLEMENTS PUBLIES PAR souv.