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1 SAFETY PRECAUTIONS
GENERAL GUIDELINES
1. IMPORTANT SAFETY NOTICE
There are special components used in this equipment
which are important for safety. These parts are marked by
in the Schematic Diagrams, Circuit Board Layout,
Exploded Views and Replacement Parts List. It is essential
that
these
critical
parts
manufacturer's specified parts to prevent shock, fire or
other hazards. Do not modify the original design without
permission of manufacturer.
2. An Isolation Transformer should always be used during the
servicing of VCR whose chassis is not isolated from the AC
power line. Use a transformer of adequate power rating as
this protects the technician from accidents resulting in
personal injury from electrical shocks. It will also protect
VCR from being damaged by accidental shorting that may
occur during servicing.
3. When servicing, observe the original lead dress. If a short
circuit is found, replace all parts which have been
overheated or damaged by the short circuit.
4. After servicing, see to it that all the protective devices such
as insulation barriers, insulation papers shields are properly
installed.
5. 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 a jumper between the two
prongs on the plug.
2. Measure the resistance value, with an ohmmeter, 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 a return path to the chassis, the reading must be
infinity.
Figure 1
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 a 1.5K ohm, 10 watts resistor, in parallel with a
0.15 microfarad capacitor, between each exposed metallic
part on the set and a good earth ground, as shown in figure
1.
should
be
replaced
with
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 and repeat each of the
above measurements.
6. The potential at any point should not exceed 0.75 volts
RMS. A leakage current tester (Simpson Model 229 or
equivalent) may be used to make the hot checks. Leakage
current must not exceed 1/2 milliamp. In case a
measurement is outside of the limits specified, there is a
possibility of a shock hazard, and the equipment should be
repaired and rechecked before it is returned to the
customer.
3
PV-9661 / PV-9662
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