Workshop Maintenance; Important Safety Notice; Esd--Sensitive Parts; Test Equipment - Nokia 445PRO Service Manual

5. Workshop Maintenance

5.1. Important Safety Notice

The components, which are important for safety, are marked with special mark ! on the circuit dia-
gram. It is essential that these critical parts should be replaced with manufacture's specified parts to
prevent X--radiation, shock, fire or other hazards.
For your own safety, use always safety isolating transformer when repairing the monitor.
5.1.1. Discharging the CRT
High voltage circuitry includes bleeder resistor which normally discharges the tube in about 5 se-
conds after the power is switched off. If you -- for safety reasons -- want to be sure about the dis-
charging, do as follows:
Wear safety goggles. A cracked CRT may implode when discharged.
The signal cable must be disconnected from the computer.
To discharge the CRT, a flat--head screwdriver with grounding cable is required.
Disconnect the signal cable.
--
Connect the metal chassis of the monitor to reliable earth.
--
Connect the grounding wire to the screwdriver.
--
Connect the other end of the grounding wire to the chassis (earth).
--
Insert the screwdriver under the rubber cap of the EHT connector to discharge the tube.
--
5.2. ESD- -Sensitive Parts
To prevent damage, when working with electrostatic discharge (ESD) sensitive parts, observe the
following instructions:
Keep the ESD--sensitive part in its original shipping container until you are ready to install the
--
part into the component card.
Just before touching the ESD--sensitive part, discharge to the monitor any static electricity in
--
your body; do this by touching the metal frame or cover of the machine. If possible, keep one
hand on the frame when inserting or removing a logic card, for example.
-- Hold the ESD--sensitive part by its edge; do not touch its pins.

5.3. Test Equipment

The following test equipment are required to adjustment procedure.
-- Safety isolating transformer
Digital multimeter: Fluke 87 or equivalent true RMS multimeter
--
High voltage probe: e.g. Fluke 80--40k
--
-- Signal generator: VTG220 + PC or programmable video generator
Colour analyzer: e.g. Minolta TV Colour Analyzer CA100
--
Convergence Gauge (CM7AR or equivalent)
--
Oscilloscope 40--100 MHz band width
--
-- Hi--Pot tester (Flash tester with insulation measurement / Leakage current / Break down voltage)
ESD protection necessary
--

5.4. Test Patterns

1 2
Black Picture
1
Signal level = 0 V at each RGB input
--
Highlight grey scale tracking
2
Signal level = 700 mV in the window at each RGB input
--
Crosshatch Picture
3
-- Squares e.g. 20 mm x 20 mm
Outmost lines correspond the active vertical/horizontal video time
--
Convergence test pattern
4
Focus test pattern
5
20
3 Active
vertical
video time
Active horizontal video time
445N
4 5
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A--- area
B--- area