Jvc THA 75 Service Manual
This is the 88 pages manual for Jvc THA 75 Service Manual.
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Extracted text from Jvc THA 75 Service Manual (Ocr-read)
Page 1
TH-A75 1-2 (No.22009) SECTION 1 Important Safety Precautions 1.1 Safety Precautions (1) This design of this product contains special hardware and many circuits and components specially for safety purposes. For continued protection, no changes should be made to the original design unless authorized in writing by the man- ufacturer. Replacement parts must be identical to those used in the original circuits. Services should be per- formed by qualified personnel only. (2) Alterations of the design or circuitry of the product should not be made. Any design alterations of the product should not be made. Any design alterations or additions will void the manufacturers warranty and will further relieve the manufacture of responsibility for personal injury or property damage resulting therefrom. (3) Many electrical and mechanical parts in the products have special safety-related characteristics. These characteris- tics are often not evident from visual inspection nor can the protection afforded by them necessarily be obtained by us- ing replacement components rated for higher voltage, watt- age, etc. Replacement parts which have these special safety characteristics are identified in the Parts List of Service Manu- al. Electrical components having such features are iden- tified by shading on the schematics and by ( ) on the Parts List in the Service Manual. The use of a substitute re- placement which does not have the same safety character- istics as the recommended replacement parts shown in the Parts List of Service Manual may create shock, fire, or oth- er hazards. (4) The leads in the products are routed and dressed with ties, clamps, tubings, barriers and the like to be separated from live parts, high temperature parts, moving parts and/or sharp edges for the prevention of electric shock and fire hazard. When service is required, the original lead routing and dress should be observed, and it should be confirmed that they have been returned to normal, after reassembling. (5) Leakage shock hazard testing) After reassembling the product, always perform an isolation check on the exposed metal parts of the product (antenna terminals, knobs, metal cabinet, screw heads, headphone jack, control shafts, etc.) to be sure the product is safe to operate without danger of electrical shock. Do not use a line isolation transformer during this check. - Plug the AC line cord directly into the AC outlet. Using a "Leakage Current Tester", measure the leakage current from each exposed metal parts of the cabinet, particular- ly any exposed metal part having a return path to the chassis, to a known good earth ground. Any leakage cur- rent must not exceed 0.5mA AC (r.m.s.). - Alternate check method Plug the AC line cord directly into the AC outlet. Use an AC voltmeter having, 1,000 ohms per volt or more sensitivity in the following manner. Connect a 1,500 ohm 10W resistor paralleled by a 0.15 µF AC-type capacitor between anexposed metal part and a known good earth ground. Measure the AC voltage across the resistor with the AC voltmeter. Move the resistor connection to each exposed metal part, particularly any exposed metal part having a return path to the chassis, and measure the AC voltage across the resistor. Now, reverse the plug in the AC outlet and repeat each measurement. Voltage measured any must not exceed 0.75 V AC (r.m.s.). This corresponds to 0.5 mA AC (r.m.s.). 1.2 Warning (1) This equipment has been designed and manufactured to meet international safety standards. (2) It is the legal responsibility of the repairer to ensure that these safety standards are maintained. (3) Repairs must be made in accordance with the relevant safety standards. (4) It is essential that safety critical components are replaced by approved parts. (5) If mains voltage selector is provided, check setting for local voltage. 1.3 Caution Burrs formed during molding may be left over on some parts of the chassis. Therefore, pay attention to such burrs in the case of pre- forming repair of this system. 1.4 Critical parts for safety In regard with component parts appearing on the silk-screen printed side (parts side) of the PWB diagrams, the parts that are printed over with black such as the resistor ( ), diode ( ) and ICP ( ) or identified by the " " mark nearby are critical for safety. When replacing them, be sure to use the parts of the same type and rating as specified by the manufacturer. (Except the JC version)
Page 2
TH-A75 (No.22009)1-3 1.5 Preventing static electricity Electrostatic discharge (ESD), which occurs when static electricity stored in the body, fabric, etc. is discharged, can destroy the laser diode in the traverse unit (optical pickup). Take care to prevent this when performing repairs. 1.5.1 Grounding to prevent damage by static electricity Static electricity in the work area can destroy the optical pickup (laser diode) in devices such as DVD players. Be careful to use proper grounding in the area where repairs are being performed. (1) Ground the workbench Ground the workbench by laying conductive material (such as a conductive sheet) or an iron plate over it before placing the traverse unit (optical pickup) on it. (2) Ground yourself Use an anti-static wrist strap to release any static electricity built up in your body. (3) Handling the optical pickup - In order to maintain quality during transport and before installation, both sides of the laser diode on the replacement optical pickup are shorted. After replacement, return the shorted parts to their original condition. (Refer to the text.) - Do not use a tester to check the condition of the laser diode in the optical pickup. The tester's internal power source can easily destroy the laser diode. 1.6 Handling the traverse unit (optical pickup) (1) Do not subject the traverse unit (optical pickup) to strong shocks, as it is a sensitive, complex unit. (2) Cut off the shorted part of the flexible cable using nippers, etc. after replacing the optical pickup. For specific details, refer to the replace- ment procedure in the text. Remove the anti-static pin when replacing the traverse unit. Be careful not to take too long a time when attaching it to the connector. (3) Handle the flexible cable carefully as it may break when subjected to strong force. (4) I t is not possible to adjust the semi-fixed resistor that adjusts the laser power. Do not turn it. 1.7 Attention when traverse unit is decomposed *Please refer to "Disassembly method" in the text for the DVD pickup unit. - Apply solder to the short land sections before the flexible wire is disconnected from the connector CN101 on the DVD servo board. (If the flexible wire is disconnected without applying solder, the DVD pickup may be destroyed by static electricity.) - In the assembly, be sure to remove solder from the short land sections after connecting the flexible wire. DVD mechanism assembly CN101 DVD servo board Short land sections Flexible wire
Page 13
TH-A75 1-14 (No.22009) 2.3.10 Removing the spindle motor board (See Figs.13 and 14.) - Remove the DVD servo board. - Remove the clamper base. - Remove the DVD traverse mechanism assembly. (1) From the top side of the DVD traverse mechanism assem- bly, remove the feed motor wire that is soldered to the spin- dle motor board. (See Fig.13.) (2) From the bottom side of the DVD traverse mechanism as- sembly, remove the three screws G attaching the spindle motor board. (See Fig.14.) Fig.13 Fig.142.3.11 Removing the feed motor (See Figs.15 to 17.) - Remove the DVD servo board. - Remove the clamper base. - Remove the DVD traverse mechanism assembly. (1) From the top side of the DVD traverse mechanism assem- bly, remove the feed motor wire that is soldered to the spin- dle motor board. (See Fig.15.) (2) Remove the screws H attaching the feed holder assembly and then take out the feed holder assembly. (See Fig.15.) (3) Remove the screw J attaching the thrust spring. (See Fig.16.) (4) Remove the feed gear and lead screw in the direction of the arrow. (See Fig.16.) (5) Remove the two screws K attaching the feed motor. (See Fig.17.) Fig.15 Fig.16 Fig.17 Remove the solders. DVD traverse mechanism assembly Spindle motor board Feed moto r wire G G DVD traverse mechanism assembly H Feed motor H Remove the solders. DVD traverse mechanism assembly Feed motor wire Spindle motor board Feed holder assembly Feed holder assembly J Feed motor Feed gear Lead screw Thrust spring Feed holder assembly K
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TH-A75 1-54 (No.22009)214 DREQ O DVD Parallel mode data request 215 DCLK I Data sampling clock 216 DSTB I Parallel mode data valid, serial mode left/right clock 217 DVD0 I DVD Drive parallel data port 218 VSSio - Connect to ground 219~223 DVD1~5 I DVD Drive parallel data port 224 VDDio - Power supply terminal 3.3V 225,226 DVD6,7 I DVD Drive parallel data port 227 MD0 I/O SDRAM Data bus terminal 228 VSSio - Connect to ground 229 MD1 I/O SDRAM Data bus terminal 230 VSS - Connect to ground 231,232 MD2,3 I/O SDRAM Data bus terminal 233 VDDio - Power supply terminal 3.3V 234~236 MD4~6 I/O SDRAM Data bus terminal 237 VSSio - Connect to ground 238~240 MD7~9 I/O SDRAM Data bus terminalPin No. Symbol Description