SAFETY PRECAUTIONS
GENERAL GUIDELINES
1. When servicing, observe the original lead
dress. If ashort circuit is found, replace all
parts which have been overheated or damaged by
the short circuit.
2. After servicing, see to it that all the
protective devices such as insulation barriers,
insulation papers shields are properly
installed.
3. After servicing, make the following leakage
current checks to prevent the customer from
being exposed to shock hazards.
LEAKAGE CURRENT COLD CHECK
1. Unplug the AC cord and connect ajumper between
the two prongs on the plug.
2. Measure the resistance value, with an ohm
meter, between the jumpered AC plug and each
exposed metallic cabinet part on the equipment
such as screwheads connectors, control
shafts, etc. When the exposed metallic part has a
return path to the chassis, the reading
should be between 1M ohm and 5.2M ohm.
When the exposed metal does not have areturn
path to the chassis, the reading must be oo.
LEAKAGE CURRENT HOT CHECK (See Figure 1)
1. Plug the AC cord directly into the AC outlet.
Do not use an isolation transformer for this
check.
2. Connect a1.5k ohm, 10 watts resistor, in
parallel with a0.1 5uF capacitor, between each
exposed metallic part on the set and agood
earth ground such as awater pipe, as shown in
Figure 1.
3. Use an AC voltmeter, with 1000 ohms/volt or
more sensitivity, to measure the potential
across the resistor.
4. Check each exposed metallic part, and measure
the voltage at each point.
5. Reverse the AC plug in the AC outlet repeat
each of the above measurements.
6. The potential at any point should not exceed
0.75 volts RMS. Aleakage current tester
(Simpson Model 229 equivalent) may be used to
make the hot checks, leakage current must not
exceed 1/2 milliamp. In case ameasurement is
outside of the limits specified, there is a
possibility of ashock hazard, and the
equipment should be repaired and rechecked
before it is returned to the customer.
ELECTROSTATICALLY SENSITIVE(ES) DEVICES
Some semiconductor (solid state) devices can be
damaged easily by static electricity. Such
components commonly are calledElectrostatically
Sensitive (ES) Devices. Examples of typical ES
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 aknown earth ground.
Alternatively, obtain and wear acommercially
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 ES 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 agrounded-tip soldering iron to
solder or unsolder ES devices.
4. Use only an anti-static solder removal device
classified as "anti-static" can generate
electrical charges sufficient to damage ES
devices.
5. Do not use freon-propelled chemicals. These can
generate electrical charges sufficient to
damage ES devices.
6. Do not remove areplacement ES device from its
protective package untilimmediately before you
are ready to install it. (Most replacementES
devices are packaged with leads eletcrically
shorted together by conductive foam, aluminum
foil or comparable conductive material).
7. Immediately before removing the protective
material from the leads of replacement ES
device, touch the protective material to the
chassis or circuit assembly into which the
device will be installed.
CAUTION :Be sure no power is applied to
the chassis or circuit, and observe all otner
asfety precautions.
8. Minimize bodily motions when handling
unpackaged replacement ES devices. (Otherwise
harmless motion such as the brushing together
of your clothes fabric or the lifting of your
foot from acarpeted floor can generate static
electricity sufficient to damage an ES device).
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