Compaq CRT Monitor s7500 Service Guide - Page 4

HP S7500/MV7500/CV7500 1 Precautions Follow these safety and servicing precautions to prevent damage and to protect against potential hazards such as electrical shock and X-rays. 1-1 Safety Precautions 1-1-1 Warnings 1. For safety purpose, do not attempt to modify thecircuit board,and always disconnect theAC power before performing servicing on the monitor. 2. Operation of the monitor outside its cabinet or with the cover removed involves the risk of shock hazard. Repair work on the monitor should onlybe attempted byservice personnel who are thoroughlyfamiliar with all necessary safety precautions and proceduresfor working onhighvoltage equipment. 3. Do not lift the CRT by the neck. After completelydischargingthe highvoltageanode, handlethe CRTonlywhen wearingshatterproof goggles. Try to keep the CRT away from the bodyduringhandling. 4. High voltageshould always be keptat the rated value, no higher. Only when high voltage is excessiveare X-rayscapable ofpenetrating the shell of the CRT. Operation at high voltages may also cause failure of the CRT or high voltage circuitry. 5. The CRT is especially constructed to limit Xrayemissionto0.5mR/HRat 300microamperes anode current. To ensure continued X-ray protection, replace theCRT withonly the same orequivalenttype as the original,andadjust the anode's voltage to the designated maximum rating, never to exceed. 1-1-2 Safety Checks Before returning the monitor to the user, perform the following safety checks: 1. Inspect to make certain that each lead dress is not pinched or that hardware is not lodged between the chassis and other metal parts in the monitor. 2. Inspect all protective devices such as Page 2 nonmetalliccontrolknobs, insulatingmaterials, cabinet backs, adjustment and compartment covers or shields, isolation resistor-capacitor networks, mechanical insulators, etc. 3. AC Leakage Current Check Always perform the AC Leakage Current Check on the exposed metal parts, including metal cabinets, screwheadsand control shafts, as follows: a) Plug the AC line cord directly into a rated AC outlet. Do not use an isolation transformer duringthe check. b) Use an AC voltmeter with at least 5000 ohms pervolt sensitivityas follows: Connect a 1500 ohms, 10 watt resistor paralleledby a0.15uF ACcapacitor inseries with all exposed metal cabinet parts and a known earth ground, such as electrical conduct or electrical ground connected to earth ground, as shown in the Figure 1-1. Measure the AC voltage across the combination of resistor and capacitor. Figure1-1. Set Up For AC Leakage Current Check To known earth ground 0.15ufd To exposed metal cabinet part 1500 ohm 10 watt c) Reverse the AC plug at the AC outlet and re pe at the ste ps fo r AC v olta ge measurements foreach exposedmetal part. d) Voltage reading must not exceed 0.3 volts RMS,equivalentto0.2 milliampereAC. Any value exceeding this limit ill constitute a potential shock hazard and must be corrected immediately.