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ETC
ETC

LA76931 Datasheet

Color TV Receiver


LA76931 Datasheet Preview


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SERVICE MANUAL
Color Television Receiver
Model: -SZ2(MONO) series
1
Page 1

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System
Channel
Scanning
IF Frequency
Sensitivity
Audio Output Power
Antenna Impedance
Power Consumption
Power Supply
SPECIFICATION
TV PAL D/K , B/G , I
AV NTSC 4.43/3.58MHz
VHF LOW
VHF HIGH
UHF
CATV
49.7585.25 MHz
168.25216.25MHz
471.25863.25 MHz
112.25464.25MHz
Line 625 Line
Horizontal Frequency 15625Hz
Vertical
50/60 Hz
Video 38MHz
Sound 31.5/32/32.5 MHz
Chroma 33.57 MHz
VHF LOW 43 dBμV
VHF HIGH 45 dBμV
UHF
45 dBμV
CATV
45 dBμV
7% THD 2W + 2W
75Ω
60W (14" series)
75W (21" series)
AC 110/220/240V 50/60Hz
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Page 2

www.DataSheet4U.com IMPORTANT SERVICE SAFETY INFORMATION
Operating the receiver outside of its cabinet or with its back removed involves a shock hazard. Work on
these models should only be performed by those who are thoroughly familiar with precautions necessary when
working on high voltage equipment.
Exercise care when servicing this chassis with power applied. Many B plus and high voltage RF terminals
are exposed which, if carelessly contacted, can cause serious shock or result in damage to the chassis. Maintain
interconnecting ground lead connections between chassis, escutcheon, picture tube dag and tuner when operating
chassis.
These receivers have a "polarized" AC line cord. The AC plug is designed to fit into standard AC outlets
in one direction only. The wide blade connects to the 'ground side' and the narrow blade connects to the 'hot
side' of the AC line. This assures that the TV receiver is properly grounded to the house wiring. If an extension
cord must be used, make sure it is of the 'polarized' type.
Since the chassis of this receive is connected to one side of the AC supply during operation, service should
not be attempted by anyone not familiar with the precautions necessary when working on these types of
equipment.
When it is necessary to make measurements or tests with AC power applied to the receiver chassis, an
Isolation Transformer must be used as a safety precaution and to prevent possible damage to transistors. The
Isolation Transformer should be connected between the TV line cord plug and the AC power outlet.
Certain HV failures can increase X-ray radiation. Receivers should not be operated with HV levels
exceeding the specified rating for their chassis type. The maximum operating HV specified for the chassis used in
these receivers is 23.5kV±1.0kV at zero beam current with a liner voltage of 120V AC. Higher voltage may also
increase the possibility of failure in the HV supply.
It is important to maintain specified values of all components in the horizontal and high voltage circuits and
anywhere else in the received that could cause a rise in high voltage, or operating supply voltages. No changes
should be made to the original design of the receiver.
Components shown in the shaded areas on the schematic diagram and/or identified by in the replacement
parts list should be replaced only with exact factory recommended replacement parts. The use of unauthorized
substitute parts man creates may create shock, fire, X-ray radiation, or other hazards.
To determine the presence of high voltage, use accurate high impedance HV meter connected between the
second anode lead and the CRT dag grounding device. When servicing the High Voltage System remove static
charges from it by connecting a 10K Ohm resistor in series with an insulated wire (such as test probe) between the
picture tube dag and 2nd anode lead (Have AC line cord disconnected from AC supply).
The picture tube used in this receiver employ integral implosion protection. Replace with a tube of the same
type number for continued safety. Do not lift picture tube by the neck. Handle the picture tube only when wearing
shatterproof goggles and after discharging the high voltage completely. Keep others without shatter proof
goggles away.
Before returning the receiver to the user, perform the following safety checks:
1. Inspect all lead dress to make certain that leads are not pinched or that hardware is not lodged between the
chassis and other metal parts in the receiver.
2. Replace all protective devices such as non-metallic control knobs, insulating fishpapers, cabinet backs,
adjustment and compartment covers of shields, isolation resistor-capacitor networks, mechanical insulators etc.
3. To be sure that not shock hazard exists, a check for the presence of leakage current should be made at
each exposed metal part having a return path to the chassis (antenna, cabinet metal, screw heads knobs and/or
shafts, escutcheon, etc.) in the following manner.
Plug the AC line cord directly into a 110V/220V/240V, AC receptacle. (Do not use an Isolation Transformer
during these checks.) All checks must be repeated with the AC line cord plug connection reversed. (If necessary, a
nonpolarized adapter plug must be used only for the purpose of completing these checks.)
If available, measure current using an accurate leakage current tester. Any reading of 0.35mA or more is
excessive and indicates a potential shock hazard, which must be corrected before returning the receiver to the
owner.
If a reliable leakage current tester is not available, this alternate method of measurement should be used.
Using two clip leads, connect a 1500 Ohm, 10 Watt resistor paralleled by a 0.15MF capacitor in series with a
known earth ground, such as a water pipe or conduit and the metal part to be checked. Use a VTVM or VOM with
1000 Ohms per Volt, or higher, sensitivity to measure this AC voltage drop across the resistor. Any reading of
0.35 Volt RMS of more is excessive and indicates potential shock hazard which must be corrected before
returning the receiver to the owner.
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Page 3

ALIGNMENT PROCEDURES
www.DataSheet4U.com PLEASE READ BEFORE ATTEMPTING SERVICE
1. Use an Isolation Transformer when performing any service on this chassis.
2. Never disconnect any leads while receiver is in operation.
3. Disconnect all power before attempting any repairs.
4. Do not short any position of the circuit while the power is on.
5. For safety reasons, replace components any with identical replacement parts (SEE PARTS LIST).
6. Before alignment, warm up the TV for at least 30 minutes and demagnetize the CRT with an external
degaussing coil.
7. When removing a PCB or related component, after unfastening or changing a wire, be sure to put the wire back
in its original position.
8. Inferior silicon grease can damage IC's and transistors. When replacing IC's and transistors, use only specified
silicon grease. Remove all old silicon when applying new silicon.
9. Before removing the anode cap, discharge eletricity because it contains high voltage.
Service Flow Chart
4
Page 4
Part Number LA76931
Manufactur ETC
Description Color TV Receiver
Total Page 20 Pages
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