Sony ST JX390 Service Manual

Page 2

ST-JX295/JX390

SAFETY CH ECK-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.

I. A commercial leakage tester, such as the
Simpson 229 or RCA WT-54OA. Follow the
manufacturers instructions to use these instru-
ments.

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 volt-
meter. The limit indication is 0.75V, so
analog meters must have an accurate low-
voltage 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 2V AC range are
suitable. (See Fig. A)

To Exposed Metal
Paris on Set

i-
§1.5kn /
L.

_ Earth Ground

A C
voltmeter

0. 75uF
{0. 75 V)

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

TABLE OF CONTENTS
Section Title Pa e
Specification ~~~~~~~~~ 1
Safety Check-out . 2

1, GENERAL

2. ELECTRICAL ADJUSTMENT

FM Section -~ 4
AM Section - 4
3. DIAGRAM
3»1_ Block Diagram ~~~~~~~~~~~~~
32. Printed Wiring Boards
33. Schematic Diagram -------
4. EXPLODED VIEWS ................................. 21
5. ELECTRICAL PARTS LIST ~~~~~~~~~~~~~~~~~~~~~ 22

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 selector to AM.

3 Press the POWER switch to turn off the unit.

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

Note

When the interval is changed. all preset stations which

you have memorized using the numeric buttons will be

erased from the memory After changing the interval, be
sure to preset the stations againr