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68
231E1 LCD
Safety Checks
After the original service problem has been corrected, a complete safety
check should be made. Be sure to check over the entire set, not just the
areas where you have worked. Some previous service may have left an
unsafe condition,
which could be unknowingly passed on to your customer. Be sure to
check all of the following:
Fire and Shock Hazard
1. Be sure all components are positioned in such a way as to avoid the
possibility of adjacent component shorts. This is especially important on
those chassis which are transported to and form the service shop.
2. Never release a repaired unit unless all protective devices such as
insulators, barries, covers, strain reliefs, and other hardware have been
installed in accordance with the original design.
3. Soldering and wiring must be inspected to locate possible cold
solder joints, solder splashes, sharp solder points, frayed leads,
pinched leads, or damaged insulation(including the accord). Be
certain to remove loose solder balls and all
other loose foreign particles.
4. Check across-the-line components and other components for physical
evidence of damage or deteriortion and replace if necessary. Follow
original layout, lead length and dress.
5. No lead or component should touch a receiving tube or a resistor rated
at1watt or more. Lead tension around protruding metal surfaces or edges
must be avoided.
6. Critical components having special safety characteristics are identified
with ans bythe Ref.No in the parts list and enclosed within a broken line
*( Where several critical components are grouped in one area) along with
the safety symbols on the schematic diagrams and/or exploded views.
7.When servicing any unit, always use a separate isolation transformer
for the chassis failure to use a separate isolation transformer may
expose you to possible shock hazard, and may cause damage to
servicing instruments.
8. Many electronic products use a polarized ac line cord(one wide pin
on the plug).
Defeating this safety feature may create a potential
hazard to the service and the user. Extension cords which do not
incorporate the polarizing feature should never be used.
9. After reassembly of the unit, always perform an leakage test or
resistance test from the line cord to all exposed metal parts of the
cabinets. Also check all metal control shafts(with knobs removed),
antenna terminals, handles, screws, etc. To be sure the unit may be
safety operated without danger of electrical
shock.
Broken line
Implosion
1. All picture tubes used in current model receivers are equipped with an
intergral implosion system care should always be used, and safety
glasses worn, whenever handling any picture tube. Avoid scratching or
other wise damaging the picture tube during installation.
2. Use only replacement tubes specified by the manufacturer.
X-radiation
1. Be sure procedures and instructions to all your service personal
cover the subject of X-radiation. Potential sources of X-rays in TV
receivers are the picture tube and the high voltage circuits. The basic
precaution which must be exercised is to keep the high voltage at the
factory recommended level.
2. To avoid possible exposure to X-radiation and electrical shock, only
the manufacturer ' s specified anode connectors must be used.
3. It is essential that the service technician has an accurate HV meter
available at all times. The calibration of this meter should be checked
periodically against a reference standard.
4. When the HV circuitry isoperating properly there is no possibility of an
X- radiation problem. High voltage should always be kept at the
manufacture, rated value-no higher- for optimum performance. Every
time a color set is serviced, the brightness should be run up and while
monitoring the HV with a meter to be certain that the HV is requation
correctly and does not exceed the specified value. We suggest that
you and your technicians review test procedures so that HV requation
are always checked as a standard servicing procedure, and the
reason for this prudent routine is cleanly understood by everyone. It is
important
ot
use
an
accurate
recommended that the HV recorded on each customer ' s invoice,
which will demonstrate a proper concern for the customer ' s safety.
5. When troubleshooting and making test measurements in a receiver with
a problem of excessive high voltage, reduce the line voltage by means of
a variac to bring the HV into acceptable limits while troubleshooting. Do not
operate the chassis loner than necessary to locate the cause of the
excessive HV.
WARNING: Before removing the back cover, turn the unit OFF and short the HIGH VOLTAGE to the ground.
Safety Check Process
and
reliable
HV
meter.
It
(safety)
6. New picture tubes are specifically designed to withstand higher
operating voltages without creating undesirable X-radiation. It is strongly
recommended that any shop test fixture which is to be used with the new
higher voltage chassis be equipped with one of the new type tubes
designed for this service. Addition of a permanently connected HV meter
to the shop test fixture is advisable. The CRT types used in these new
sets should never be replaced with any other types, as this may result in
excessive X-radiation.
7. It is essential to use the specified picture tube to avoid a possible
X-radiation problem.
8. Most TV receivers contain come types of emergency" Hold Down"
circuit to prevent HV from rising to excessive levels in the presence
of a failure mode.
These various circuits should be understood by all technicians
servicing them, especially since many hold down circuits are
inoperative as long as the receiver performs normally.
Leakage Current Cold Check
1. Unplug the ac line cord and connect a jumper between the two
prongs of the plug.
2. Turn on the power switch.
3. Measure the resistance value between the jumpered ac plug and
all exposed cabinet parts of the receiver, such as screw heads,
antennas, and control shafts. When the exposed metallic part has a
return path to the chassis, the reading should be between 1 megohm
and 5.2 megohms. When the exposed metal does not have a return
path to the chassis, the reading must be infinity. Remove the jumper
from the ac line cord.
To
INSTRUMENTS
EXPOSED
METAL
PARTS
1500 ohm, 10W 0.15uF
Leakage Current Hot Check
1. Do not use an isolation transformer for this test. Plug the
completely reassembled receiver directly into the ac outlet.
2. Connect a 1.5k, 10w resistor paralleled by a 0.15uf capacitor between
each exposed metallic cabinet part and a good earth ground such as a
water pipe, as shown above.
3. Use an ac voltmeter with at least 5000
measure the potential across the resistor.
4. The potential at any point should not exceed 0.75 volts. A
leakage current tester may be used to make this test; leakage
current must not exceed a possibility of shock hazard. The
receiver should be repaired and rechecked before returning it to
the customer.
5. Repeat the above procedure with the ac plug reversed.(note: an
ac adapter is necessary when a polarized plug is used. Do not
defeat the polarizing
feature of the plug.)
Picture Tube Replacement
The primary source of X-radiation in this television receiver is the
picture tube. The picture tube utilized in this chassis is specially
constructed to limit X-radiation emissions. For continued X-radiation
protection, the replacement tube must be the same types as the
original, including suffix letter, or a Philips approved tube.
Parts Replacement
Many electrical and mechanical parts in Philips television sets have
is
specialsafety related characteristics. These characteristics are often not
evident from visual inspection nor can the protection afforded by them
necessarily be
obtained by using replacement components r=ated for higher voltage,
wattage, etc. The use of a substitute part which does not have the
same safety characteristics as the Philips recommended
replacement part should in this service manual may create shock, fire,
or other hazards
WATER
PIPE
EARTH
GROUND
ohms volt sensitivity to
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