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— 5 —

1) Before returning an instrument to the customer, always make a

safety check of the entire instrument, including, but not limited
to, the following items:

(1) Be sure that no built-in protective devices are defective or have

been defeated during servicing.
(1)Protective shields are provided to protect both the technician
and the customer. Correctly replace all missing protective
shields, including any removed for servicing convenience.
(2)When reinstalling the chassis and/or other assembly in the
cabinet, be sure to put back in place all protective devices,
including, but not limited to, nonmetallic control knobs,
insulating fish papers, adjustment and compartment covers/
shields, and isolation resistor/capacitor networks. Do not operate
this instrument or permit it to be operated without all protective
devices correctly installed and functioning.

(2) Be sure that there are no cabinet openings through which adults

or children might be able to insert their fingers and contact a
hazardous voltage. Such openings include, but are not limited
to, excessively wide cabinet ventilation slots, and an improperly
fitted and/or incorrectly secured cabinet back cover.

(3) Leakage Current Hot Check-With the instrument completely

reassembled, plug the AC line cord directly into a 120V AC
outlet. (Do not use an isolation transformer during this test.)
Use a leakage current tester or a metering system that complies
with American National Standards institute (ANSI) C101.1
Leakage Current for Appliances and Underwriters Laboratories
(UL) 1270 (40.7). With the instrument’s AC switch first in the
ON position and then in the OFF position, measure from a known
earth ground (metal water pipe, conduit, etc.) to all exposed
metal parts of the instrument (antennas, handle brackets, metal
cabinets, screwheads, metallic overlays, control shafts, etc.),
especially any exposed metal parts that offer an electrical return
path to the chassis.
Any current measured must not exceed 0.5mA. Reverse the
instrument power cord plug in the outlet and repeat the test. See
Fig. 1.
Any measurements not within the limits specified herein indicate
a potential shock hazard that must be eliminated before returning
the instrument to the customer.

(4) Insulation Resistance Test Cold Check-(1) Unplug the power

supply cord and connect a jumper wire between the two prongs
of the plug. (2) Turn on the power switch of the instrument. (3)
Measure the resistance with an ohmmeter between the jumpered
AC plug and all exposed metallic cabinet parts on the instrument,
such as screwheads, antenna, control shafts, handle brackets,
etc. When an exposed metallic part has a return path to the
chassis, the reading should be between 1 and 5.2 megohm. When
there is no return path to the chassis, the reading must be infinite.
If the reading is not within the limits specified, there is the
possibility of a shock hazard, and the instrument must be repared
and rechecked before it is returned to the customer. See Fig. 2.

DEVICE

UNDER

TEST

(READING SHOULD

NOT BE ABOVE

0.5mA)

LEAKAGE

CURRENT

TESTER

EARTH

GROUND

TEST ALL

EXPOSED METER

SURFACES

ALSO TEST WITH
PLUG REVERSED

(USING AC ADAPTER
PLUG AS REQUIRED)

2-WIRE CORD

Fig. 1 AC Leakage Test

Fig. 2 Insulation Resistance Test

2) Read and comply with all caution and safety related notes on or

inside the cabinet, or on the chassis.

3) Design Alteration Warning-Do not alter or add to the mechanical

or electrical design of this instrument. Design alterations and
additions, including but not limited to, circuit modifications and
the addition of items such as auxiliary audio output connections,
might alter the safety characteristics of this instrument and create
a hazard to the user. Any design alterations or additions will
make you, the servicer, responsible for personal injury or
property damage resulting therefrom.

4) Observe original lead dress. Take extra care to assure correct

lead dress in the following areas:
(1) near sharp edges, (2) near thermally hot parts (be sure that
leads and components do not touch thermally hot parts), (3) the
AC supply, (4) high voltage, and (5) antenna wiring. Always
inspect in all areas for pinched, out-of-place, or frayed wiring,
Do not change spacing between a component and the printed-
circuit board. Check the AC power cord for damage.

5) Components, parts, and/or wiring that appear to have overheated

or that are otherwise damaged should be replaced with
components, parts and/ or wiring that meet original
specifications.
Additionally, determine the cause of overheating and/or damage
and, if necessary, take corrective action to remove any potential
safety hazard.

Antenna
Terminal

Exposed
Metal Part

ohm

ohmmeter

— 6 —

6) Product Safety Notice-Some electrical and mechanical parts

have special safety-related characteristics which are often not
evident from visual inspection, nor can the protection they give
necessarily be obtained by replacing them with components rated
for higher voltage, wattage, etc. Parts that have special safety
characteristics are identified by shading, an (

) or a (

) on

schematics and parts lists. Use of a substitute replacement that
does not have the same safety characteristics as the
recommended replacement part might create shock, fire and/or
other hazards. Product safety is under review continuously and
new instructions are issued whenever appropriate.

— 7 —

 Before servicing units covered by this service manual

and its supplements, read and follow the Safety Precautions section
of this manual.

  If unforseen circumstances create conflict between the

following servicing precautions and any of the safety precautions,
always follow the safety precautions. Remember: Safety First.

(1) a. Always unplug the instrument’s AC power cord from the AC

power source before (1) re-moving or reinstalling any
component, circuit board, module or any other instrument
assembly, (2) disconnecting any instrument electrical plug or
other electrical connection, (3) connecting a test substitute in
parallel with an electrolytic capacitor in the instrument.

b. Do not defeat any plug/socket B+ voltage interlocks with

which instruments covered by this service manual might be
equipped.

c. Do not apply AC power to this instrument and/or any of its

electrical assemblies unless all solid-state device heat sinks
are correctly installed.

d. Always connect a test instrument’s ground lead to the

instrument chassis ground before connecting the test
instrument positive lead. Always remove the test instrument
ground lead last.

 Refer to the Safety Precautions section ground lead last.

(2) The service precautions are indicated or printed on the cabinet,

chassis or components. When servicing, follow the printed or
indicated service precautions and service materials.

(3) The components used in the unit have a specified flame

resistance and dielectric strength.
When replacing components, use components which have the
same ratings. Components identified by shading, by (

) or by

(

) in the circuit diagram are important for safety or for the

characteristics of the unit. Always replace them with the exact
replacement components.

(4) An insulation tube or tape is sometimes used and some

components are raised above the printed wiring board for safety.
The internal wiring is sometimes clamped to prevent contact
with heating components. Install such elements as they were.

(5) After servicing, always check that the removed screws,

components, and wiring have been installed correctly and that
the portion around the serviced part has not been damaged and
so on. Further, check the insulation between the blades of the
attachment plug and accessible conductive parts.

Disconnect the attachment plug from the AC outlet and turn the
power ON. Connect the insulation resistance meter (500V) to the
blades of the attachment plug. The insulation resistance between
each blade of the attachment plug and accessible conductive parts
(see note) should be more than 1 Megohm.

 Accessible conductive parts include metal panels, input

terminals, earphone jacks, etc.

— 8 —

Some semiconductor (solid state) devices can be damaged easily
by static electricity.
Such components commonly are called Electrostatically Sensitive
Devices (ESD). Examples of typical ESD devices are integrated
circuits and some field-effect transistors and semiconductor chip
components. The following techniques should be used to help reduce
the incidence of component damage caused by static electricity.

(1) Immediately before handling any semiconductor component or

semiconductor-equipped assembly, drain off any electrostatic
charge on your body by touching a known earth ground.
Alternatively, obtain and wear a commercially available
discharging wrist strap device, which should be removed for
potential shock reasons prior to applying power to the unit under
test.

(2) After removing an electrical assembly equipped with ESD

devices, place the assembly on a conductive surface such as
aluminum foil, to prevent electrostatic charge buildup or
exposure of the assembly.

(3) Use only a grounded-tip soldering iron to solder or unsolder

ESD devices.

(4) Use only an anti-static solder removal devices. Some solder

removal devices not classified as “anti-static” can generate
electrical charges sufficient to damage ESD devices.

(5) Do not use freon-propelled chemicals. These can generate

electrical charges sufficient to damage ESD devices.

(6) Do not remove a replacement ESD device from its protective

package until immediately before your are ready to install it.
(Most replacement ESD devices are packaged with leads
electrically shorted together by conductive foam, aluminum foil
or comparable conductive materials).

(7) Immediately before removing the protective materials from the

leads of a replacement ESD device, touch the protective material
to the chassis or circuit assembly into which the device will be
installed.

 Be sure no power is applied to the chassis or circuit,

and observe all other safety precautions.

(8) Minimize bodily motions when handling unpackaged

replacement ESD devices. (Otherwise harmless motion such as
the brushing together of your clothes fabric or the lifting of
your foot from a carpeted floor can generate static electricity
sufficient to damage an ESD device).