Panasonic SA-VK680EE Service Manual

41 Safety Precautions1.1. GENERAL GUIDELINES1. When servicing, observe the original lead dress. If a short circuit is found, replace all parts which have been overheated ordamaged by the short circuit.2. After servicing, see to it that all the protective devices such as insulation barriers, insulation papers shields are properlyinstalled.3. After servicing, carry out the following leakage current checks to prevent the customer from being exposed to shock hazards.1.1.1. LEAKAGE CURRENT COLD CHECK1. 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 onthe equipment such as screwheads, connectors, control shafts, etc. When the exposed metallic part has a return path to thechassis, the reading should be between 1MΩ and 5.2MΩ.When the exposed metal does not have a return path to the chassis, the reading must be1.1.2. LEAKAGE CURRENT HOT CHECK1. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check.2. Connect a 1.5kΩ, 10 watts resistor, in parallel with a 0.15μF capacitors, between each exposed metallic part on the set and agood earth ground such as a water 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 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 thelimits specified, there is a possibility of a shock hazard, and the equipment should be repaired and rechecked before it isreturned to the customer.Figure 11.2. Before Repair and AdjustmentDisconnect AC power to discharge unit AC Capacitors as such (C5700, C5701, C5703, C5704, C5705, C5706, C5707) through a10 Ω, 10 W resistor to ground.Caution:DO NOT SHORT-CIRCUIT DIRECTLY (with a screwdriver blade, for instance), as this may destroy solid state devices.After repairs are completed, restore power gradually using a variac, to avoid overcurrent.Current consumption at AC 230V, 50 Hz at power on (in FM Tuner, no signal at volume minimum) should be ~ 500 mA.1.2.1. Caution for fuse replacement1.3. Protection CircuitryThe 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