Dell E773c Series, Service Manual

Page: 5 / 50

5
2. PRECAUTIONS AND NOTICES
2-1 SAFETY PRECAUTIONS
1. Observe all caution and safety related notes located inside the display cabinet.
2. Operation of the display with the cover removed, may cause a serious shock hazard from the
display power supply. Work on the display should not be attempted by anyone who is not
thoroughly familiar with precautions necessary when working on high voltage equipment.
3. Do not install, remove or handle the picture tube in any manner unless shatter-proof goggles are
worn. People who are not so equipped should be kept away while handling picture tube. Keep
picture tube away from the body while handling.
4. The picture tube is constructed to limit X-RAY radiation to 0.5 mR/HR. For continued protection,
use the designated replacement tube only, and adjust the voltages so that the designated
maximum rating at the anode will not be exceeded.
5. Symbol“ “ means safety relative parts. The use of substitute replacement parts which do not
have the same characteristics as specified in the parts list may create shock, fire or explode etc.
6. Symbol “ ” means X-ray relative parts. Before replacing any of these components please
read the parts list in this manual carefully to avoid creating higher anode voltage or x-ray.
Especially for sealed controls, such as VR902 and FBT screen VR etc, which were sealed by the
manufacturer once their optimum position has been set, please don’t dismantle them as your
likes, otherwise you will break or damage the component. If you need replace the parts with
sealed control, please adjust the relative VR to make sure the B+ voltage about 66.0V and well
seal it with A+B glue or equivalent, which you can not move away with one screw driver
7. Before returning a serviced display to the customer, a thorough safety test must be performed to
verify that the display is safe to operate without danger or shock. Always perform an AC leakage
current check on the exposed metallic parts of the cabinet, such as screw heads.
Test method for current leakage is described as follow.
(a) Plug the AC line cord directly into rated AC outlet (do not use a line isolation transformer
during this check).
(b) Use an AC voltmeter having 5000 ohms per volt or with more sensitivity in the following
manner: Connect a 1500 ohms 10 Watt resistor, paralleled by a 0.15UF, AC type capacitor
between a known good earth ground (water pipe, conduit, etc.) and the exposed metallic
parts simultaneously. Measure the AC voltage across the combination of 1500 ohms
resistor and 0.15UF capacitor.
(c) Reverse the AC plug at the AC outlet and repeat AC voltage measurements for each
exposed metallic part.
(d) Voltage measured must not exceed 0.5 volts RMS. This corresponds to 0.35 milliamp AC.
Any value exceeding this limit constitutes a potential shock hazard and must be corrected
immediately.