Panasonic AG520VDH - COMB. DVD/VCR/TV, Service Manual

Page: 3 / 100

1 SAFETY PRECAUTIONS
1.1. GENERAL GUIDELINES
1. IMPORTANT SAFETY NOTICE
There are special components used in this equipment
which are important for safety. These parts are marked by
in the Schematic Diagrams, Circuit Board Layout,
Exploded Views and Replacement Parts List. It is essential
that
these critical parts should be replaced with
manufacturer’s specified parts to prevent X-RADIATION,
shock, fire, or other hazards. Do not modify the original
design without permission of manufacturer.
2. An Isolation Transformer should always be used during the
servicing of Combination DVD VCR whose chassis is not
isolated from the AC power line. Use a transformer of
adequate power rating as this protects the technician from
accidents resulting in personal injury from electrical shocks.
It will also protect Combination DVD VCR from being
damaged by accidental shorting that may occur during
servicing.
3. When servicing, observe the original lead dress, especially
the lead dress in the high voltage circuits. If a short circuit is
found, replace all parts which have been overheated or
damaged by the short circuit.
4. After servicing, see to it that all the protective devices such
as insulation barriers, insulation papers, shield, and
isolation R-C combinations are properly installed.
5. Before turning the receiver on, measure the resistance
between B+ line and chassis ground. Connect (-) side of an
ohmmeter to the B+ lines, and (+) side to chassis ground.
Each line should have more resistance than specified, as
follows :
B+ Line Minimum Resistance
130 V 110
Ω
(Cold chassis ground)
28 V 180
Ω
(Cold chassis ground)
220 V 1 k
Ω
(Cold chassis ground)
6. When the TV set is not used for a long period of time,
unplug the power cord from the AC outlet.
7. Potentials, as high as 33.0 kV are present when this TV set
is in operation. Operation of the TV set without the rear
cover involves the danger of a shock hazard from the TV
set power supply. Servicing should not be attempted by
anyone who is not thoroughly familiar with the precautions
necessary when working on high voltage equipment.
Always discharge the anode of the picture tube to the CRT
ground of receiver before handling the tube.
8. After servicing make the following leakage current checks to
prevent the customer from being exposed to shock
hazards.
1.2. LEAKAGE CURRENT COLD
CHECK
1. Unplug the AC cord and connect a jumper between the two
prongs on the plug.
2. For physically operated power switches, turn power on.
Otherwise skip step 2.
3. Measure the resistance value, with an ohmmeter, between
the jumpered AC plug and each exposed metallic cabinet
part on the receiver, such as screwheads, connectors, etc.
When the exposed metallic part has a return path to the
chassis, the reading should be between 1 M
Ω
and 12 M
Ω
.
When the exposed metal does not have a return path to the
chassis, the reading must be infinity.
1.3. LEAKAGE CURRENT HOT
CHECK
1. Plug the AC cord directly into the AC outlet.
Do not use a isolation transformer for this check.
2. Connect a 1.5 k
Ω
, 10 W resistor, in parallel with a 0.15 µF
capacitor, between each exposed metallic part on the set
and a good earth ground, as shown in Figure 1.
3. Use an AC voltmeter, with 1 k
Ω
/V or more sensitivity, to
measure the potential across the resistor.
4. Check each exposed metallic part, and measure the
voltage at each point.
5. Reverse the AC plug in the AC outlet and repeat each of the
above measurements.
6. The potential at any point should not exceed 0.75 V RMS.
A leakage current tester (Simpson Model 229 equivalent)
may be used to make the hot checks. Leakage current must
not exceed 1/2 mA. In case a measurement is outside of
the limits specified, there is a possibility of shock hazard,
and the receiver should be repaired and rechecked before
it is returned to the customer.
Figure 1
3
AG-520VDH