Sanyo DP26648 Service Manual - Page 2

SAFETY INSTRUCTIONS SAFETY PRECAUTIONS WARNING: The chassis of this receiver has a floating ground with the potential of one half the AC line voltage in respect to earth ground. Service should not be attempted by anyone not familiar with the precautions necessary when working on this type of equipment. The following precautions must be observed: 1. An isolation transformer must be connected in the power line between the receiver and the AC line before any service is performed on the receiver. 2. Comply with all caution and safety-related notes provided inside the cabinet, on the chassis, and on the back. 3. When replacing a chassis in the cabinet, always be certain that all the protective devices are installed properly, such as control knobs, adjustment covers, shields and barriers. 4. Before replacing the back cover of the set, thoroughly inspect the inside of the cabinet to see that no stray parts or tools have been left inside. Before returning any television to the customer, the service technician must perform the following safety checks to be sure that the unit is completely safe to operate without danger of electrical shock. ANTENNA COLD CHECK Remove AC plug from the 120 VAC outlet and place a jumper across the two blades. Connect one lead of an ohmmeter to the jumpered AC plug, and touch the other lead to each exposed antenna terminal (UHF and VHF antenna terminals). The resistance must measure between 1M ohm and 5.2M ohm. Any resistance value below or above this range indicates an abnormality which requires corrective action. LEAKAGE CURRENT CHECK Plug the AC line cord directly into a 120 VAC outlet. (Do not use an isolation transformer for this check.) Use an AC voltmeter, that has 5000 ohms per volt or more sensitivity. Connect a 1500 ohm 10 watt resistor, paralleled by a 0.15 µF 150 VAC capacitor, between a known good earth ground (water pipe, conduit, etc.) and all exposed metal parts of the cabinet (antennas, handle bracket, metal cabinet, screw heads, metal overlays, control shafts, etc.). Measure the AC voltage across the 1500 ohm resistor. The AC voltage should not exceed 750 mV. A reading exceeding 750 mV indicates that a dangerous potential exists. The fault must be located and corrected. Repeat the above test with the receiver power plug reversed. NEVER RETURN A RECEIVER TO THE CUSTOMER WITHOUT TAKING THE NECESSARY CORRECTIVE ACTION. PRODUCT SAFETY NOTICE When replacing components in a receiver, always keep in mind the necessary product safety precautions. Pay special attention to the replacement of components marked with a in the parts list and in the schematic diagrams. To ensure safe product operation, it is necessary to replace those components with the exact same PARTS. READING SHOULD NOT EXCEED 750 mV. AC VOLTMETER (5000 ohms per volt or more sensitivity) TELEVISION RECEIVER 1500 ohm 10 watt Good earth ground such as a water pipe, conduit, etc. 0.15 μF 150V AC AC OUTLET To be touched to all of exposed metal parts. Voltmeter Hook-up for Leakage Current Check. SERVICING ELECTROSTATICALLY SENSATIVE DEVICES Semiconductors (solid-state devices) that can be damaged by static electricity are referred to as Electrostatically Sensitive (ES) devices. Examples of typical ES devices are: Integrated Circuits (IC), Field-Effect Transistors (FET), and "chip" components. The following techniques should be observed strictly, to reduce the occurrence of semiconductor damage due to electrostatic discharge. 1. Immediately prior to handling any semiconductor component or an assembly containing a semiconductor device or devices, discharge the electrostatic buildup on your body by touching a known earth ground. You may also obtain and wear a commercially available discharging wrist strap device. CAUTION: Be sure to remove the wrist strap before applying power to any unit being serviced. 2. After removing an ES equipped assembly, place it on a conductive surface, such as, aluminum foil, to prevent buildup or exposure to static electricity. 3. Use only grounded-tip soldering irons to solder or unsolder ES devices. 4. Use only anti-static solder removal devices. Some suction-type devices can generate static electricity adequate to damage ES devices. 5. A replacement ES device will come packaged in protective material (conductive foam, aluminum foil, or some comparable conductive material). Do Not remove an ES device from its protective packaging unless you are prepared to install it immediately. 6. Precisely prior to removing an ES device from its protective packaging, touch the protective packaging to the chassis or assembly in which the device will be installed. CAUTION: Be sure that no power is applied to the chassis or circuit assembly. 7. Incidental body movements, such as, lifting a foot from a carpeted floor or the rubbing of fabric together can generate static electricity sufficient to damage ES devices. Therefore, minimize all body movements while handling exposed (unpackaged) ES devices. -2-