Philips 20PT643F Manuel utilisateur

IMPORTANT SAFETY NOTICE

Proper service and repair is important to the safe, reliable operation of all Philips

Consumer Electronics Company** Equipment. The service procedures recommended by

Philips and described in this service manual are effective methods of performing service

operations. Some of these service operations require the use of tools specially designed

for the purpose. The special tools should be used when and as recommended.

It is important to note that this manual contains various CAUTIONS and NOTICES

which should be carefully read in order to minimize the risk of personal injury to service

personnel. The possibility exists that improper service methods may damage the

equipment. It also is important to understand that these CAUTIONS and NOTICES

ARE NOT EXHAUSTIVE. Philips could not possibly know, evaluate and advise the

service trade of all conceivable ways in which service might be done, or of the possible

hazardous consequences of each way. Consequently, Philips has not undertaken any such

broad evaluation. Accordingly, a servicer who uses a service procedure or tool which is

not recommended by Philips must first satisfy himself thoroughly that neither his safety

nor the safe operation of the equipment will be jeopardized by the service method

selected.

** Hereafter throughout this manual, Philips Consumer Electronics Company will be

referred to as Philips.

WARNING

Critical components having special safety characteristics are identified with a or

"S" by the 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 symbol

on the schematics or exploded views. Use of substitute replacement parts which

do not have the same specified safety characteristics may create shock, fire, or other

hazards. Under no circumstances should the original design be modified or altered

without written permission from Philips. Philips assumes no liability, express or

implied, arising out of any unauthorized modification of design. Servicer assumes all

liability.

* Broken Line ____ _ ____ _ ____ _ ____

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 from the service shop.

2.Never release a repaired unit unless all protective devices such as insulators, barriers, 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 ac cord). 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

deterioration 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 at 1 watt or more. Lead tension

around protruding metal surfaces or edges must be avoided.

6.Critical components having special safety characteristics are identified with an 'S' by the 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 symbol 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 servicer 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 ac leakage test or resistance test from the line cord to all

exposed metal parts of the cabinet. Also, check all metal control shafts (with knobs removed), antenna

terminals, handles, screws, etc., to be sure the unit may be safely operated without danger of electrical

shock.

* Broken line ____ _ ____ _ ____ _ ____

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 below.

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 0.5mA. If a measurement is outside of the specified limits,

there is 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.)

With the instrument completely reassembled, plug the ac line cord directly into a 120Vac outlet. (Do not

use an isolation transformer during this test.) Use a leakage current tester or a metering system that

complies with American National Standards Institute (ANSI) C101.1 Leakage Current for Appliances and

Underwriters Laboratories (UL) 1410, (50.7). With the instrument ac switch first in the on position and

then in the off position, measure from a known earth ground (metal water pipe, conduit, etc.) to all exposed

metal parts of the instrument (antennas, handle brackets, metal cabinet, screw heads, metallic overlays,

control shafts, etc.), especially any exposed metal parts that offer an electrical return path to the chassis.

Any current measured must not exceed 0.5mA. Reverse the instrument power cord plug in the outlet and

repeat the test. See the graphic below.

TV SAFETY NOTES

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 servicer 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

Implosion

X-Radiation

Leakage Current Cold Check

Leakage Current Hot Check

Picture Tube Replacement

Parts Replacement

WARNING: Before removing the CRT anode cap, turn the unit OFF and short the HIGH VOLTAGE to

the CRT DAG ground.

SERVICE NOTE: The CRT DAG is not at chassis ground.

IMPLOSION

1.All picture tubes used in current model receivers are equipped with an integral implosion system.

Care should always be used, and safety glasses worn, whenever handling any picture tube. Avoid

scratching or otherwise 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 personnel 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 is operating properly there is no possibility of an X-radiation problem. High

voltage should always be kept at the manufacturer's rated value -no higher -for optimum

performance. Every time a color set is serviced, the brightness should be run up and down while

monitoring the HV with a meter to be certain that the HV is regulated correctly and does not exceed

the specified value. We suggest that you and your technicians review test procedures so that HV and

HV regulation are always checked as a standard servicing procedure, and the reason for this prudent

routine is clearly understood by everyone. It is important to use an accurate and reliable HV meter. It

is recommended that the HV reading be 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 longer 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 some type 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.

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 type as the original, including suffix letter,

or a Philips approved type.

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 rated 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 shown in this service manual may create shock, fire, or other

hazards.

PRODUCT SAFETY GUIDELINES FOR ALL PRODUCTS

CAUTION: Do not modify any circuit. Service work should be performed only after you are thoroughly

familiar with all of the following safety checks. Risk of potential hazards and injury to the user increases if

safety checks are not adhered to.

USE A SEPARATE ISOLATION TRANSFORMER FOR THIS UNIT WHEN SERVICING.

PREVENTION OF ELECTROSTATIC DISCHARGE (ESD)

Some semiconductor solid state devices can be damaged easily by static electricity. Such components

commonly are called Electrostatically Sensitive (ES) Devices, Examples of typical ES devices are

integrated circuits and some field-effect transistors and semiconductor "chip" components. The following

techniques should be used to help reduce the incidence of component damage caused by electrostatic

discharge (ESD).

1.Immediately before handling any semiconductor component or semiconductor-equipped assembly, drain

off any ESD on your body by touching a known earth ground. Alternatively, obtain and wear a

commercially available discharging ESD wrist strap, which should be removed for potential shock

reasons prior to applying power to the unit under test.

2.After removing an electrical assembly equipped with ES devices, place the assembly on a conductive

surface such as aluminum foil, to prevent electrostatic charge buildup or exposure of the assembly.

3.Use only a grounded-tip soldering iron to solder or unsolder ES devices.

4.Use only an anti-static solder removal device. Some solder removal devices not classified as "antistatic

(ESD protected)" can generate an electrical charge sufficient to damage ES devices.

5.Do not use Freon propelled chemicals. These can generate electrical charges sufficient to damage ES

devices.

6.Do not remove a replacement ES device from its protective package until immediately before you are

ready to install it (most replacement ES devices are packaged with leads electrically shorted together by

conductive foam, aluminum foil or comparable conductive material).

7.Immediately before removing the protective material from the leads of a replacement ES device, touch

the protective material to the chassis or circuit assembly into which the device will be installed.

CAUTION: Be sure no power is applied to the chassis or circuit and observe all other safety precautions.

8.Minimize bodily motions when handling unpackaged replacement ES devices. (Otherwise harmless

motion such as the brushing together of your clothes fabric or the lifting of your feet from a carpeted

floor can generate static electricity (ESD) sufficient to damage an ES device.)

NOTE to CATV system Installer:

This reminder is provided to call the CATV system installer's attention to article 820-22 of the NEC that

provides guidelines for proper grounding and, in particular, specifies that the cable ground shall be

connected to the grounding system of the building, as close to the point of cable entry as practical.

PRACTICAL SERVICE PRECAUTIONS

IT MAKES SENSE TO AVOID EXPOSURE TO ELECTRICAL SHOCK. While some sources are

expected to have a possible dangerous impact, others of quite high potential are of limited current and are

sometimes held in less regard.

ALWAYS RESPECT VOLTAGES. While some may not be dangerous in themselves, they can cause

unexpected reactions –reactions that are best avoided. Before reaching into the powered color TV set, it is

best to test the high voltage insulation. It is easy to do, and is just a good service precaution.

BEFORE POWERING UP THE TV WITH THE BACK OFF (or on a test fixture), attach a clip lead to

the CRT DAG ground and to a screwdriver blade that has a well insulated handle. After the TV is powered

on and high voltage has developed, probe the anode lead with the blade, starting at the bottom of the High

Voltage Transformer (flyback –IFT). Move the blade to within two inches of the connector of the CRT. IF

THERE IS AN ARC, YOU FOUND IT THE EASY WAY, WITHOUT GETTING A SHOCK! If

there is an arc to the screwdriver blade, replace the High Voltage Transformer or the lead, (if removable)

whichever is causing the problem.

PICTURE TUBE REPLACEMENT PROCEDURE

Note: a. Two (2) people are required to handle this picture tube.

b. Safety Glasses must be worn during this procedure or whenever directly handling a picture tube.

c. Take care in each step not to damage the CRT or the cabinet.

1.Remove the Chassis and the CRT Socket Board Module from the cabinet.

2.A furniture pad or blanket should be positioned on the floor to support only the CRT Face. This pad or

blanket should be high enough to keep the CRT Face approximately 12 to 14 inches off the floor.

3.Using two people, place the cabinet in a front down position with the CRT Face on the pad or blanket.

4.Place padded blocks under each corner of the cabinet to keep it from rocking.

5.Remove the four screws, at the corners of the CRT.

6.With two people lowering the cabinet to the floor, leave the CRT elevated by the pad or blanket.

Note: Take care not to grasp the neck of the CRT during this procedure, as it is extremely fragile.

7.Two (2) people may then lift the CRT from the cabinet.

8.Remove the degaussing coil from the defective CRT and mount on the replacement. Take care to

maintain the exact shape and fit.

To install the new CRT, reverse steps 1 to 7.

Technical Specifications and Connections

Note: Described specifications are valid for the whole product range.

Technical Specifications

Reception

Feature Data

Tuning system :

PLL

Color systems :

NTSC M/N

Sound systems :

BTSC non-DBX

BTSC DBX

Channel selections :

181, full cable

IF picture carrier :

45.75 MHz

Aerial input :

75 Ohm, F-type

A/V Connections :

NTSC M/N

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