Precautions - NEC MultiSync V720 Service Manual

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 the circuit board, and always disconnect the AC 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 only be attempted by service personnel who are thoroughly
familiar with all necessary safety precautions and procedures for working on high voltage equipment.
3. Do not lift the CRT by the neck. After completely discharging the high voltage anode, handle the CRT
only when wearing shatterproof goggles. Try to keep the CRT away from the body during handling.
4. High voltage should always be kept at the rated value, no higher. Only when high voltage is excessive
are X-rays capable of penetrating 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 X-ray emission to 0.5mR/HR at 300 microamperes anode
current. To ensure continued X-ray protection, replace the CRT with only the same or equivalent type
as the original, and adjust 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 nonmetallic control knobs, insulating materials, 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,
screwheads and control shafts, as follows:
a) Plug the AC line cord directly into a rated AC outlet. Do not use an isolation transformer during the
check.
b) Use an AC voltmeter with at least 5000 ohms per volt sensitivity as follows:
Connect a 1500 ohms, 10 watt resistor paralleled by a 0.15uF AC capacitor in series with all ex-
posed 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 combi-
nation of resistor and capacitor.
Figure 1-1. Set Up For AC Leakage Current Check
To known
Earth ground
0.15ufd
1500 ohm 10 watt
To exposed metal
Cabinet part
1