SERVICE MANUAL Product Type: Chassis: Manual Series: Manual Part #: Model Line: Product Year: Commercial Directview TV CL SR24 923-03508 E 2002 Model Series: H20E35DT HPK20E35DT HW20E35DT H25E34Y H25E35DT HW25E35DT H25E39Y H27E35DT HPK27E35DT H27E35S H27E35DT8 H27E35S8 H32E35DT CONTENTS Overview ...................................................... 1 Service Menu ................................................ 2 Servicing ..................................................... 3 Parts ........................................................... 4 Diagrams ...................................................... 5 Schematics ................................................... 6 Published October 2002 by Technical Publications Zenith Electronics Corporation 201 James Record Road Huntsville, Alabama 35824-1513 Copyright Printed in U.S.A. 2002 by Zenith Electronics Corporation PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO-VIDEO PRODUCTS IMPORTANT SAFETY NOTICE This Manual was prepared for use only by properly trained audio-visual service technicians. When servicing this product, under no circumstances should the original design be modified or altered without permission from Zenith Electronics Corporation. All components should be replaced only with types identical to those in the original circuit and their physical location, wiring and lead dress must conform to original layout upon completion of repairs. Special components are also used to prevent x-radiation, shock and fire hazard. These components are indicated by the letter "x" included in their component designators and are required to maintain safe performance. No deviations are allowed without prior approval by Zenith Electronics Corporation. Circuit diagrams may occasionally differ from the actual circuit used. This way, implementation of the latest safety and performance improvement changes into the set is not delayed until the new service literature is printed. Caution: Do not attempt to modify this product in any way. Never perform customized installations without manufacturer's approval. Unauthorized modifications will not only void the warranty, but may lead to property damage or user injury. Service work should be performed only after you are thoroughly familiar with these safety checks and servicing guidelines. GRAPHIC SYMBOLS The exclamation point within an equilateral triangle is intended to alert the service personnel to important safety information in the service literature. The lightning flash with arrowhead symbol within an equilateral triangle is intended to alert the service personnel to the presence of non-insulated "dangerous voltage" that may be of sufficient magnitude to constitute a risk of electric shock. The pictorial representation of a fuse and its rating within an equilateral triangle is intended to convey to the service personnel the following fuse replacement caution notice: CAUTION: FOR CONTINUED PROTECTION AGAINST RISK OF FIRE, REPLACE ALL FUSES WITH THE SAME TYPE AND RATING AS MARKED NEAR EACH FUSE. SERVICE INFORMATION While servicing, use an isolation transformer for protection from AC line shock. After the original service problem has been corrected, make a check of the following: FIRE AND SHOCK HAZARD 1. Be sure that all components are positioned to avoid a possibility of adjacent component shorts. This is especially important on items transported to and from the repair shop. 2. Verify that all protective devices as such as insulators, barriers, covers, shields, strain reliefs, power supply cords, and other hardware have been reinstalled per the original design. Be sure that the safety purpose of the polarized line plug has not been defeated. 3. Soldering must be inspected to discover possible cold solder joints, solder splashes, or sharp solder points. Be certain to remove all loose foreign particles. 4. Check for physical evidence of damage or deterioration to parts and components, for frayed leads or damaged insulation (including the AC cord), and replace if necessary. 5. No lead or component should touch a receiving tube or a resistor rated at 1 watt or more. Lead tension around protruding metal surfaces must be avoided. 6. After re-assembly of the set, always perform an AC leakage test on all exposed metallic parts of the cabinet (the channel selector knobs, antenna terminals, handle and screws) to be sure that set is safe to operate without danger of electrical shock. DO NOT USE A LINE ISOLATION TRANSFORMER DURING THIS TEST. Use an AC voltmeter having 5000 ohm, 10 watt resistor, paralleled by a .15 mfd 150V AC type capacitor between a known good earth ground (water pipe, conduit, etc.) and the exposed metallic parts, one at a time. Measure the AC voltage across the combination of 1500 ohm resistor and .15 mfd capacitor. Reverse the AC plug by using a non-polarized adaptor and repeat AC voltage measures for each exposed metallic part. Voltage measured must not exceed 0.75 volts RMS. This corresponds to 0.5 milliamp AC. Any value exceeding this limit constitutes a potential shock hazard and must be corrected immediately. A.C. Voltmeter 0.15uF Good Earth Ground such as the Water Pipe, Conduit, etc. 1500 OHM Place this probe on each exposed metal part. 10 WATT X-RADIATION 1.Be sure procedures and instructions to all service personnel cover the subject of x-radiation. The only potential source of x-rays in current TV receivers is the picture tube. However, this tube does not emit x-rays when the HV is at the factory-specified level. The proper value is given on the applicable schematic. Operation at higher voltages may cause a failure of the picture tube or high-voltage supply and, under certain circumstances, may produce radiation in excess of desirable levels. 2.Only factory-specified CRT anode connectors must be used. 3.It is essential that the service personnel have available an accurate and reliable high-voltage meter 4.When the high-voltage circuitry is operating properly, there is no possibility of an x-radiation problem. Every time a color chassis is serviced, the brightness should be run up and down while monitoring the high voltage with a meter, to be certain that the high voltage does not exceed the specified value and that it is regulating correctly. 5.When troubleshooting and making test measurements in a product with a problem of excessively high voltage, avoid being unnecessarily close the picture tube and the high voltage power supply. Do not operate the product longer than necessary to locate the cause of excessive voltage. 6.Refer to HV, B+, and shutdown adjustment procedures described in the appropriate schematics and diagrams (where used). IMPLOSION 1.All direct view picture tubes are equipped with an integral implosion protection system; take care to avoid damage during installation. 2.Use only the recommended factory replacement tubes. TIPS ON PROPER INSTALLATION 1.Never install any receiver in a closed-in recess, cubbyhole, or closely fitting shelf space over, or close to, a heat duct, or in the path of heated air flow. 2.Avoid conditions of high humidity such as: outdoor patio installations where dew is a factor, near steam radiators where steam leakage is a factor, etc. 3.Avoid placement where draperies may obstruct venting. The customer should also avoid the use of decorative scarves or other coverings that might obstruct ventilation. 4.Wall and shelf-mounted installations using a commercial mounting kit must follow the factory-approved mounting instructions. A product mounted to a shelf or platform must retain its original feet (or the equivalent thickness in spacers) to provide adequate air flow across the bottom. Bolts or screws used for fasteners must not touch any parts or wiring. Perform leakage tests on customized installations. 5.Caution customers against mounting a product on a sloping shelf or in a titled position, unless the receiver is properly secured. 6.A product on a roll-about cart should be stable in its mounting to the cart. Caution the customer on the hazards of trying to roll a cart with small casters across thresholds or deep pile carpets. 7.Caution customers against using a cart or stand that has not been listed by Underwriters Laboratories, Inc. for use with its specific model of television receiver or generically approved for use with TVs of the same or larger screen size 8.Caution customers against using extension cords. Explain that a forest of extensions, sprouting from a single outlet, can lead to disastrous consequences to home and family. SR24 - 923-03508 i CL - SAFETY PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO-VIDEO PRODUCTS X-RADIATION To prevent possible exposure to radiation caused by excessive CRT Anode voltage, the CH/CL Chassis incorporates a "High Voltage Shutdown" circuit. This circuit senses the level of flyback pulse from the "Flyback Transformer" representative of the actual high voltage on the CRT anode. When this level exceeds a predetermined voltage, the circuit shuts down the horizontal drive, preventing further generation of anode voltage. In this condition, the horizontal drive is "latched" off for about 5 seconds, after which, restart is attempted. SHUTDOWN CIRCUIT OPERATION The flyback pulse voltage from Pin 6 of TX3201 (Flyback Transformer) is peak detected (rectified) by the action of diode D3000 and capacitor C3001. This forms a DC voltage appearing on C3001 representative of the CRT anode voltage (HV) produced by T3201. This voltage is divided down by precision resistors RX3001, RX3002, & RX3003. This lower voltage, appear on the positive input of IC3101. If the CRT anode voltage becomes excessive, pin 5 of IC3101 will be higher than the negative input of pin 6. This will cause the output of pin 7 to rise to approximately 15 volts. This signal (SD_DRV) is sent to the base of Q4000 causing the Horizontal Drive to be disabled and latched, which causes the HV to shutdown. In about 5 seconds, the shutdown circuit resets (Pins 8, 9 & 14 of IC2900), the Horizontal Drive and HV will be reestablished. The circuit formed by Q3104, C3108, C3113, D3107, R3134, R3132, R3131, and R3133 disables the HV compensation output (Q3102-B signal) during turn on and shutdown conditions (transients). CRT ANODE HIGH VOLTAGE MEASUREMENT PROCEDURE Each CRT screen has its own safe operating Anode Voltage and shutdown voltage. Critical Safety components (designed with an `X' in the component designator) are designed to operate the CRT at a safe operating Anode voltage and provide proper shutdown thresholds. If replacement of any of these components are deemed necessary, it is important to use original type Zenith replacement components. After a replacement is made, confirm proper Anode voltage using the following procedure. Measurement of the CRT Anode voltage must be performed with no visible raster on the screen and operating at nominal horizontal scanning frequency 37.9 khz (TV or SVGA signal). After discharging the CRT, connect a high impedance high voltage meter to the CRT anode. Turn the television `On' and confirm a good signal is being displayed. Reduce Brightness and Contrast settings until the picture is well extinguished. Observe the Anode voltage meter reading and compare with the table below for the proper CRT screen size. If the voltage reading is higher than the maximum, verify circuit component values and proper operation. HV SHUTDOWN MEASUREMENT PROCEDURE 1. Adjust the beam current to OmA in NTSC mode. 2. Apply a variable DC voltage to pin 10 of the PDT1 connector, from 20 to 0 VDC, starting at 20 VDC. 3. Slowly decrease supply towards zero. 4. Remove DC voltage from pin 10 of PTD1. 5. After approximately 5 seconds, verify that the HV must be reestablished (High Voltage Reset). SHUTDOWN SAFETY CIRCUIT D3003 103-471A R3006 D3001 RX3001 P/L R3004 1K RX3000 H-FLYBK +15 PDR 103-471A C3113 10uF 50V +15 PDR 47K R3134 2.7K C3108 .0047 Q3102-B D3000 103-344-02A RX3002 P/L C3001 10MF 100V RX3003 10K 1% C3002 0.1 50V 5 3 2 6 4 7 1 8 SD-DRV 50V R3132 10K C D3107 R3131 B E R3133 1K 100 F.S. IC3101 5V REF 221-240 Q3104 121-1310A 103-471A 4.7K TP3004 SL SL SL SL SL SR24 - 923-03508 ii CL - SAFETY - iii - TABLE OF CONTENTS SECTION 1 .................... OVERVIEW OVERVIEW ..................................................... 1-1 INTERFACES ................................................... 1-2 LT-2000 CLONE PROGRAMMER ........................... 1-5 USER MENUS .................................................. 1-7 SETUP MENU .............................................. 1-7 AUDIO MENU .............................................. 1-8 VIDEO MENU ............................................... 1-8 PARENTAL CONTROL ...................................... 1-8 ON-SCREEN DISPLAYS ................................... 1-9 MPAA RATING SYSTEM ................................ 1-10 TV PARENTAL GUIDELINE RATING SYSTEM ....... 1-10 SECTION 4 PARTS PARTS .............................. ...