Hitachi 42V710 Service Manual

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LC48/B-LC47/B/K

SERVICING PRECAUTIONS
CAUTION: Before servicing instruments covered by this service data and its supplements and addenda, read and follow the SAFETY PRECAUTIONS on page 2 of this publication. NOTE: If unforseen circumstances create conflict between the following SERVICING PRECAUTIONS and any of the SAFETY PRECAUTIONS on page 2 of this publication, always follow the SAFETY PRECAUTIONS. Remember: Safety First. General Servicing Guidelines 1. Always unplug the instrument AC power cord from the AC power source before: a. Removing or reinstalling any component, circuit board, module, or any other instrument assembly. b. Disconnecting or reconnecting any instrument electrical plug or other electrical connection. Connecting a test substitute in parallel with an electrolytic capacitor in the instrument. CAUTION: A wrong part substitution or incorrect polarity installation of electrolytic capacitors may result in an explosion hazard. 1. Immediately before handling any semiconductor component or semiconductor-equipped assembly, drain off a
ny electrostatic charge on your body by touching a known earth ground. Alternatively, obtain and wear a commercially available discharging wrist strap device, which should be removed for potential shock reasons prior to applying power to the unit under test. After removing an electrical assembly equipped with ES devices, place the assembly on a conductive surface such as aluminum foil, to prevent electrostatic charge build-up or exposure of the assembly. Use only a grounded-tip soldering iron to solder or desolder ES devices. Use only an anti-static type solder removal device. Some solder removal devices not classified as "anti-static" can generate electrical charges sufficient to damage ES device. Do not use freon-propelled chemicals. These can generate electrical charges sufficient to damage ES devices. Do not remove a replacement ES device from its protective package until immediately before you are ready to install it. (Most replacement ES devices are packaged with leads electrically shorted together by
conductive foam, aluminum foil or comparable conductive material.) Immediately before removing the protective material from the leads of a replacement ES device, touch the protective material to the chassis or circuit assembly into which the device will be installed. CAUTION: Be sure no power is applied to the chassis or circuit, and observe all other safety precautions. Minimize bodily motions when handling unpackaged replacement ES devices. (Otherwise harmless motion such as the brushing together of your clothes fabric or the lifting of your foot from a carpeted floor can generate static electricity sufficient to damage an ES device.)

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Do not spray chemicals on or near this instrument or any of its assemblies. Unless specified otherwise in these service data, clean electrical contacts by applying the following mixture to the contacts with a pipe cleaner, cotton-tipped stick or comparable nonabrasive applicator: 10% (by volume) Acetone and 90% (by volume) ispropyle alchohol (90%-99% strength). CAUTION: This is a flammable mixture. Unless specified otherwise in these service data, lubrication of contacts is not required. Do not defeat any plug/socket B+ voltage interlocks with which instruments covered by this service data might be equipped. 7.

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Do not apply AC power to this instrument and/or any of its electrical assemblies unless all solid-state device heat-sinks are correctly installed. Always connect the test instrument ground lead to the appropriate instrument chassis ground before connecting the test instrument positive lead. Always remove the test instrument ground lead last. Use with this instrument only the test fixtures specified in this service data. CAUTION: Do not connect the test fixture ground strap to any heatsink in this instrument.

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Electrostatically Sensitive (ES) Devices Some semiconductor (solid state) devices can be damaged easily by static electricity. Such components commonly are called Electrostatically Sensitive (ES) Devices. Examples of typical ES devices are integrated circuits and some field-effect transistors and semiconductor "chip" components. The following techniques should be used to help reduce the incidence of component damage caused by static electricity.

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TABLE OF CONTENTS

LC48/B-LC47/B/K General Soldering Guidelines 1. Use a grounded-tip, low-wattage soldering iron and appropriate tip size and shape that will maintain tip temperature within the range 500°F to 600°F. 2. Use an appropriate lead free solder (see page 10). Lead solder can be used, but there is a possibility of failure due to insufficient strength of the solder. 3. 4. Keep the soldering iron tip clean and well-tinned. Thoroughly clean the surfaces to be soldered. Use a small wirebristle (0.5 inch or 1.25 cm) brush with a metal handle. Do not use freon-propelled spray-on cleaners. Use the following desoldering technique. a. Allow the soldering iron tip to reach normal temperature (500°F to 600°F). b. Heat the component lead until the solder melts. Quickly draw away the melted solder with an anti-static, suctiontype solder removal device or with solder braid. CAUTION: Work quickly to avoid overheating the circuit board printed foil. 3. 2. Draw away the melted solder with an anti-static suction-type sol der removal
device (or with solder braid) before removing the IC.

Replacement 1. Carefully insert the replacement IC in the circuit board. 2. Carefully bend each IC lead against the circuit foil pad and solder it. Clean the soldered areas with a small wire-bristle brush. (It is not necessary to reapply acrylic coating to areas.)

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"Small-signal" Discrete Transistor Removal/Replacement 1. Remove the defective transistor by clipping its leads as close as possible to the component body. 2. Bend into a "U" shape the end of each of three leads remaining on the circuit board. Bend into a "U" shape the replacement transistor leads. Connect to replacement transistor leads to the corresponding leads extending from the circuit board and crimp the "U" with long nose pliers to insure metal to metal contact, then solder each connection.

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Use the following soldering technique. a. Allow the sodering iron tip to reach normal temperature (500°F to 600°F). b. First, hold the soldering iron tip and solder strand against the component lead until the solder melts. Quickly move the soldering iron tip to the junction of the component lead and the printed circuit foil, and hold it there only until the solder flows onto and around both the component lead and the foil. CAUTION: Work quickly to avoid overheating the circuit board printed foil or components. Closely inspect the solder area and remove any excess or splashed solder with a small wire-bristle brush.

Power Output Transistor Devices Removal/Replacement 1. Heat and remove all solder from around the transistor leads. 2. 3. 4. 5. 6. Remove the heatsink mounting screw (if so equipped). Carefully remove the transistor from the circuit board. Insert new transistor in circuit board. Solder each transistor lead, and clip off excess lead. Replace heatsink.

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Diode Removal/Replacement 1. Remove defective diode by clipping its leads as close as possilbe to diode body. 2. Bend the two remaining leads perpendicularly to the circuit board. Observing diode polarity, wrap each lead of the new diode around the corresponding lead on the circuit board. Securely crimp each connection and solder it. Inspect (on the circuit board copper side) the solder joints of the two "original leads". If they are not shiny, reheat them and, if necessary, apply additional solder.

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Use Soldering Iron to Pry Leads

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IC Removal/Replacement Some Hitachi unitized chassis circuit boards have slotted holes (oblong) through which the IC leads are inserted and then bent flat against the circuit foil. When holes are the slotted type, the following technique should be used to remove and replace the IC. When working with boards using the familiar round hole, use the standard technique as outlined in paragraphs 5 and 6 above. Removal 1. Desolder and straighten each IC lead in one operation by gently prying up on the lead with the soldering iron tip as the solder melts.

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LC48/B-LC47/B/K Fuses and conventional Resistor Removal/Replacement 1. Clip each fuse or resistor lead at top of circuit board hollow stake. 2. Securely crimp leads of replacement component around stake 1/8 inch from top. Solder the connections. CAUTION: Maintain original spacing between the replaced component and adjacent components and the circuit board, to prevent excessive component temperatures.

At Other Connections Use the following technique to repair defective copper pattern at con-

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DEFECTIVE COPPER REMOVED

Circuit Board Foil Repair Excessive heat applied to the copper foil of any printed circuit board will weaken the adhesive that bonds the foil to the circuit board, causing the foil to separate from, or "lift-off" the board. The following guidelines and procedures should be followed whenever this condition is encountered. In Critical Copper Pattern Areas High component/copper pattern density and/or special voltage/current characteristics make the spacing and integrity of copper pattern in some circuit board areas more critical than in others. The circuit foil in these area is designated as Critical Copper Pattern. Because Critical Copper Pattern requires special soldering techniques to ensure the maintenance of reliability and safety standards, contact your Hitachi personnel. At IC Connections To repair defective copper pattern at IC connections, use the following procedure to install a jumper wire on the copper pattern side of the circuit board. (Use this technique only on IC connections.) 1. Carefully remov
e the damaged copper pattern with a sharp knife. (Remove only as much copper as absolutely necessary.) 2. Carefully scratch away the solder resist and acrylic coating (if used) from the end of the remaining copper pattern.

Insulated Jumper Wire nections other than IC Pins. This technique involves the installation of a jumper wire on the component side of the circuit board. 1. Remove the defective copper pattern with a sharp knife. Remove at least 1/4 inch of copper, to ensure hazardous condition will not exist if the jumper wire opens. 2. Trace along the copper pattern from both wire sides of the pattern break and locate the nearest component directly connected to the affected copper pattern. Connect insulated 20-gauge jumper wire from the nearest component on one side of the pattern break to the lead of the nearest component on the other side. Carefully crimp and solder the connections. CAUTION: Be sure the insulated jumper wire is dressed so that it does not touch components or sharp edges.

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BARE JUMPER WIRE

Frequency Synthesis (FS) Tuning Systems 1. Always unplug the instrument AC power cord before disconnecting or reconnecting FS tuning system cables and before removing or inserting FS tuning system modules. 2. The FS tuner must never be disconnected from the FS tuning control module while the power is applied to the instrument. When troubleshooting intermittent problems that might be caused by defective cable connection(s) to the FS tuning system, remove the instrument AC power as soon as the defective connector is found and finish confirming the bad connection with a continuity test. This procedure will reduce the probability of electrical overstress of the FS system semi-conductor components.

CRIMP AND SOLDER

3. Install Jumper Wire and Solder 3. Bend a small "U" in one end of a small-gauge jumper wire and carefully crimp it around the IC pin. Solder the IC connection. Route the jumper wire along the path of the cut-away copper pattern and let it overlap the previously scraped end of the good copper pattern. Solder the overlapped area, and clip off any excess jumper wire.

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