Sanyo DS31590 Service Manual

Also see for DS31590: Owner's manual

Contents

— 2 —SAFETY PRECAUTIONSWARNING: The chassis of this receiver has a floatingground with the potential of one half the AC line voltage inrespect to earth ground. Service should not be attempted byanyone not familiar with the precautions necessary whenworking on this type of equipment.The following precautions must be observed:1. An isolation transformer must be connected in the powerline between the receiver and the AC line before any ser-vice is performed on the receiver.2. Comply with all caution and safety-related notes provid-ed on the side of the cabinet, inside the cabinet, on thechassis, and the picture tube.3. When replacing a chassis in the cabinet, always be cer-tain that all the protective devices are installed properly,such as control knobs, adjustment covers, shields andbarriers.DO NOT OPERATE THIS TELEVISION RECEIVERWITHOUT THE PROTECTIVE SHIELD IN POSITION ANDPROPERLY SECURED.4. Before replacing the back cover of the set, thoroughlyinspect the inside of the cabinet to see that no stray partsor tools have been left inside.Before returning any television to the customer, theservice technician must perform the following safetychecks to be sure that the unit is completely safe tooperate without danger of electrical shock.ANTENNA COLD CHECKRemove AC plug from the 120 VAC outlet and place ajumper across the two blades. Connect one lead of an ohm-meter to the jumpered AC plug, and touch the other lead toeach exposed antenna terminal (UHF and VHF antenna ter-minals). The resistance must measure between 1M ohmand 5.2M ohm. Any resistance value below or above thisrange indicates an abnormality which requires correctiveaction.LEAKAGE CURRENT CHECKPlug the AC line cord directly into a 120 VAC outlet. (Do notuse an isolation transformer for this check.) Use an AC volt-meter, that has 5000 ohms per volt or more sensitivity.Connect a 1500 ohm 10 watt resistor, paralleled by a 0.15 μF150 VAC capacitor, between a known good earth ground(water pipe, conduit, etc.) and all exposed metal parts of thecabinet (antennas, handle bracket, metal cabinet, screwheads, metal overlays, control shafts, etc.). Measure the ACvoltage across the 1500 ohm resistor. The AC voltageshould not exceed 750 mV. A reading exceeding 750 mVindicates that a dangerous potential exists. The fault mustbe located and corrected. Repeat the above test with thereceiver power plug reversed.NEVER RETURN A RECEIVER TO THE CUSTOMERWITHOUT TAKING THE NECESSARY CORRECTIVE ACTION.X-RADIATION PRECAUTIONThe primary source of X-RADIATION in solid-state receivers isthe picture tube. The picture tube is specially constructed tolimit X-Ray emission. For continued X-RADIATION protection,the replacement tube must be the same type as the original(including the suffix letter in the part numbers). Excessive highvoltage may produce potentially hazardous X-RADIATION. Toavoid such hazards, the high voltage must be maintained withinspecific limits. Refer to the X-RADIATION WARNING NOTE onthe CHASSIS SCHEMATIC in this service manual for specifichigh voltage limits. If the high voltage exceeds specified limits,check the components specified on the chassis schematicdiagram and take the necessary corrective action. Carefullyfollow the instructions for the +B Voltage Check and the HighVoltage Check to maintain the high voltage within the specifiedlimits.HIGH VOLTAGE HOLD-DOWN TESTTo prevent X-RADIATION from the picture tube due toexcessive high voltage, a HOLD-DOWN circuit is provided inthe high voltage circuit. Every time the receiver is serviced,the high voltage HOLD-DOWN circuit must be tested forproper operation. Refer to the HIGH VOLTAGE HOLD-DOWN TEST in service adjustments.PRODUCT SAFETY NOTICEWhen replacing components in a receiver, always keep inmind the necessary product safety precautions. Pay specialattention to the replacement of components marked with aSAFETY INSTRUCTIONS