Panasonic PV-M2738 Operating, Service Manual

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1-1
EARTH GROUND
1500
Ω
. 10W
0.15
µ
F
AC VOLTMETER
Hot-Check Circuit
TO
APPLIANCES
EXPOSED
METAL PARTS
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 VCR whose chassis is not iso-
lated from the AC power line. Use a transformer of ad-
equate power rating as this protects the technician from
accidents resulting in personal injury from electrical shocks.
It will also protect Combination 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 isola-
tion 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
130V 1K ohm (Hot chassis ground)
27V 180 ohms (Cold chassis ground)
17V 110 ohms (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 32.0KV 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. Al-
ways 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.
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 ohm and 12
M ohms. When the exposed metal does not have a return
path to the chassis, the reading must be infinity.
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 1.5K ohms, 10 watts resistor, in parallel with a
0.15 micro farad capacitor, between each exposed metal-
lic part on the set and a good earth ground , as shown in
Figure 1.
3. Use an AC voltmeter, with 1000 ohms/volt or more sensi-
tivity, to measure the potential across the resistor.
4. Check each exposed metallic part, and measure the volt-
age 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 volt RMS.
A leakage current tester (Simpson Model 229 equivalent)
may be used to make the hot checks. Leakage current
must not exceed 1/2 milliampere. 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
X-RADIATION
WARNING :
1. The potential source of X-Radiation in TV sets is the High
Voltage section and the picture tube.
2. When using a picture tube test fixture for service, ensure
that the fixture is capable of handling 32.0KV without
causing X-Radiation.
NOTE :
It is important to use an accurate periodically calibrated
high voltage meter.
1. Reduce the brightness to minimum.
2. Set the SERVICE switch to SERVICE .
3. Measure the High Voltage. The meter reading should indi-
cate 30.0 +/- 2.0KV .
If the meter indication is out of tolerance, immediate service
and correction is required to prevent the possibility of
premature component failure.
4. To prevent an X-Radiation possibly, it is essential to use the
specified picture tube.
SAFETY PRECAUTIONS