SAMSUNG 793DF Service Manual Precaution

1 Precautions

!

DEVICE
UNDER
TEST

TEST ALL

EXPOSED METAL

SURFACES

(READING SHOULD

NOT BE ABOVE 0.5mA)

LEAKAGE
CURRENT

TESTER

2-WIRE CORD

ALSO TEST WITH

PLUG REVERSED
(USING AC ADAPTER
PLUG AS REQUIRED)

EARTH

GROUND

1-1 Safety Precautions

WARNINGS

1. For continued safety, do not attempt to modify the
circuit board.

2. Disconnect the AC power before servicing.

3. When the chassis is operating, semiconductor
heatsinks are potential shock hazards.

1-1-1 Servicing the High Voltage circuit

and CRT :

1. When servicing the high voltage circuit, remove the
static charge by connecting a 10 kohm resistor in
series with an insulated wire (such as a test probe)
between the chassis and the anode lead.

2. When troubleshooting a monitor with excessively
HV, avoid being unnecessarily close to the monitor.
Do not operate the monitor for longer than is
necessary to locate the cause of excessive voltage.

3. High voltage should always be kept at the rated
value, no higher. Only when high voltage is
excessive are X-rays capable of penetrating the shell
of the CRT, including the lead in glass material.
Operation at high voltages may also cause failure of
the CRT or high voltage circuitry.

4. When the HV regulator is operating properly, there
is no possibility of an X-ray problem. Make sure the
HV does not exceed its specified value and that it is
regulating correctly.

5. The CRT is especially designed to prohibit
X-ray emissions. To ensure continued X-ray
protection, replace the CRT only with one that is
the same or equivalent type as the original.

6. Handle the CRT only when wearing shatterproof
goggles and after completely discharging the high
voltage anode.

7. Do not lift the CRT by the neck.

2. Inspect all protective devices such as nonmetallic
control knobs, insulating materials, cabinet backs,
adjustment and compartment covers or shields,
isolation resistor-capacitor networks, mechanical
insulators, etc.

3. Leakage Current Hot Check (Figure 1-1):

WARNING: 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
Publication UL1410, 59.7).

4. With the unit completely reassembled, plug the AC
line cord directly into a 120V AC outlet. With the
unit’s AC switch first in the ON position and then
OFF, measure the current between a known earth
ground (metal water pipe, conduit, etc.) and all
exposed metal parts, including: metal cabinets,
screwheads and control shafts. The current
measured should not exceed 0.5 milliamp. Reverse
the power-plug prongs in the AC outlet and repeat
the test.

1-1-2 Fire and Shock Hazard :

Before returning the monitor to the user, perform the
following safety checks:

1. Inspect each lead dress to make certain that the
leads are not pinched or that hardware is not
lodged between the chassis and other metal parts in
the monitor.

1-1-3 Product Safety Notices

Some electrical and mechanical parts have special
safety-related characteristics which are often not
evident from visual inspection. The protection they give
may not be obtained by replacing them with
components rated for higher voltage, wattage, etc. Parts

Figure 1-1. Leakage Current Test Circuit

that have special safety characteristics are identified by

on schematics and parts lists. A substitute
replacement that does not have the same safety
characteristics as the recommended replacement part
might create shock, fire and / or other hazards. Product
safety is under review continuously and new

LE15V*/LE17LS/LE17LT/

LE17KS/LE17KT/LE17JS/LE17JT

instructions are issued whenever appropriate.

Components identified by on schematics and parts
lists must be sealed by a soldering iron after
replacement and adjustment.

1-1

1 Precautions

1-2 Servicing Precautions

WARNING1: First read the “Safety Precautions” section of this manual. If unforeseen circumstances

create conflict between the servicing precautions and safety precautions, always
follow the safety precautions.

WARNING2: A high voltage VR replaced in the wrong direction may cause excessive X-ray

emissions.

WARNING3: An electrolytic capacitor installed with the wrong polarity might explode.

1. Servicing precautions are printed on the cabinet,
and should be followed closely.

2. Always unplug the unit’s AC power cord from the
AC power source before attempting to: (a) remove
or reinstall any component or assembly, (b)
disconnect PCB plugs or connectors, (c) connect all
test components in parallel with an electrolytic
capacitor.

3. Some components are raised above the printed
circuit board for safety. An insulation tube or tape
is sometimes used. The internal wiring is
sometimes clamped to prevent contact with
thermally hot components. Reinstall all such
elements to their original position.

4. After servicing, always check that the screws,
components and wiring have been correctly
reinstalled. Make sure that the area around the
serviced part has not been damaged.

5. Check the insulation between the blades of the AC
plug and accessible conductive parts (examples:
metal panels, input terminals and earphone jacks).

6. Insulation Checking Procedure: Disconnect the
power cord from the AC source and turn the power
switch ON. Connect an insulation resistance meter
(500 V) to the blades of the AC plug.

The insulation resistance between each blade of the
AC plug and accessible conductive parts (see
above) should be greater than 1 megohm.

7. Never defeat any of the +B voltage interlocks. Do
not apply AC power to the unit (or any of its
assemblies) unless all solid-state heat sinks are
correctly installed.

8. Always connect a test instrument’s ground lead to
the instrument chassis ground before connecting
the positive lead; always remove the instrument’s
ground lead last.

1-3 Electrostatically Sensitive Devices (ESD) Precautions

Some semiconductor (solid state) devices can be easily damaged by static electricity. Such components are commonly
called Electrostatically Sensitive Devices (ESD). Examples of typical ESD are integrated circuits and some field-effect
transistors. The following techniques will reduce the incidence of component damage caused by static electricity.

1. Immediately before handling any semiconductor
components or assemblies, drain the electrostatic
charge from your body by touching a known earth
ground. Alternatively, wear a discharging wrist­strap device. To avoid a shock hazard, be sure to
remove the wrist strap before applying power to
the monitor.

2. After removing an ESD-equipped assembly, place it
on a conductive surface such as aluminum foil to
prevent accumulation of an electrostatic charge.

3. Do not use freon-propelled chemicals. These can
generate electrical charges sufficient to damage
ESDs.

4. Use only a grounded-tip soldering iron to solder or
desolder ESDs.

5. Use only an anti-static solder removal device. Some
solder removal devices not classified as “anti-static”
can generate electrical charges sufficient to damage
ESDs.

6. Do not remove a replacement ESD from its
protective package until you are ready to install it.
Most replacement ESDs are packaged with leads
that are electrically shorted together by conductive
foam, aluminum foil or other conductive materials.

7. Immediately before removing the protective
material from the leads of a replacement ESD,
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 body motions when handling
unpackaged replacement ESDs. Motions such as
brushing clothes together, or lifting your foot from
a carpeted floor can generate enough static
electricity to damage an ESD.

9. Indicates ESDs on the Schematic Diagram in
this manual.

1-2 LE15V*/LE17LS/LE17LT/

LE17KS/LE17KT/LE17JS/LE17JT