Safety Precautions; General Guidelines; Leakage Current Cold Check; Leakage Current Hot Check (See Figure 1.) - Panasonic SC-HTB690EB Service Manual

1 Safety Precautions

1.1. General Guidelines

1. IMPORTANT SAFETY NOTICE
There are special components used in this equipment which are important for safety. These parts are marked by
the Schematic Diagrams, Circuit Board Layout, Exploded Views and Replacement Parts List. It is essential that these
critical parts should be replaced with manufacturer's specified parts to prevent X-RADIATION, 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 AC Adaptor 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 AC Adaptor 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.

1.2. 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 thechassis, the reading should be between 1 MΩ and 5.2 MΩ. When the exposed metal does not have a return path
to the chas-sis, the reading must be infinity.
1.3. 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 1.5 kΩ, 10 W resistor, in parallel with a 0.15 μF capacitor, between each exposed metallic part on the set and
a good earth ground, as shown in Figure. 1.
3. Use an AC voltmeter, with 1 kΩ/V 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 V RMS. A leakage current tester (Simpson Model 229 or equivalent)
maybe used to make the hot checks, leakage current must not exceed 1/2 mA. In case a measurement is outside of the
limitsspecified, there is a possibility of a shock hazard, and the equipment should be repaired and rechecked before it is
returned tothe customer.

1.4. Protection Circuitry

The protection circuitry may have operated if either of the following conditions are noticed:
• No sound is heard when the power is turned on.
• Sound stops during a performance.
The function of this circuitry is to prevent circuitry damage if, for example, the positive and negative speaker connection wires
are"shorted", or if speaker systems with an impedance less than the indicated rated impedance of the amplifier are used.If this
occurs, follow the procedure outlines below:
1. Turn off the power.
2. Determine the cause of the problem and correct it.
3. Turn on the power once again after one minute.
Note:
When the protection circuitry functions, the unit will not operate unless the power is first turned off and then on again
Figure. 1
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