Philips 190EW9FB 00 Service Manual Download Page 62

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190EW9 LCD

Safety Check Process

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  and  reliable  HV  meter.  It  is
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.

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.

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 ohms volt sensitivity to
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

special safety 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

WARNING:

Before

removing

the

back

cover,

turn

the

unit

OFF

and

short