Sharp 21FL94 Service Manual - Page 5

21FL94 Note: INSTALLATION AND SERVICE INSTRUCTIONS (1) When performing any adjustments to resistor controls and transformers use non-metallic screwdrivers or TV alignment tools. (2) Before performing adjustments, the TV set must be on at least 15 minutes. CIRCUIT PROTECTION The receiver is protected by a 3.15A fuse (F701), mounted on PWB-A, wired into one side of the AC line input. X-RADIATION PROTECTOR CIRCUIT TEST After service has been performed on the horizontal deflection system, high voltage system, B+ system, test the X-Radiation protection circuit to ascertain proper operation as follows: 1. Apply 110~220V AC using a variac transformer for accurate input voltage. 2. Allow for warm up and adjust all customer controls for normal picture and sound. 3. Receive a good local channel. 4. Connect a digital voltmeter to P603 pin3 and make sure that the voltmeter reads 20 ±1.1V. 5. Apply external 27V DC at P603 pin3 by using an external DC supply, TV must be shut off. 6. To reset the protector, unplug the AC cord and make a short circuit between P603 pin1 and P603 pin2. Now make sure that normal picture appears on the screen. 7. If the operation of the horizontal oscillator does not stop in step 5, the circuit must be repaired before the set is returned to the customer. HIGH VOLTAGE CHECK High voltage is not adjustable but must be checked to verify that the receiver is operating within safe and efficient design limitations as specified checks should be as follows: 1. Connect an accurate high voltage meter between ground and anode of picture tube. 2. Operate receiver for at least 15 minutes at 110~220V AC line voltage, with a strong air signal or a properly tuned in test signal. 3. Enter the service mode and set Y-mute ON by using Service R/C. 4. The voltage should be approximately 28.7kV (at zero beam). If a correct reading cannot be obtained, check circuitry for malfunctioning components. After the voltage test, make Y-mute off to the normal mode. 5