Sharp 14LK20A User manual

1
14LK20A
COLOR TELEVISION
Chassis No. SN-70A
In the interests of user-safety (Required by safety regulations in some countries) the set should be restored to its
original condition and only parts identical to those specified should be used.
S49F614LK20A/
»ELECTRICAL SPECIFICATIONS......................................................................................................... 1
»IMPORTANT SERVICE SAFETY PRECAUTION ................................................................................2
»LOCATION OF USER'S CONTROL.....................................................................................................4
»INSTALLATION AND SERVICE INSTRUCTIONS ...............................................................................5
»CHASSIS LAYOUT ............................................................................................................................ 10
»BLOCK DIAGRAM ..............................................................................................................................11
»DESCRIPTION OF SCHEMATIC DIAGRAMS ................................................................................... 12
»SCHEMATIC DIAGRAMS .................................................................................................................. 13
»PRINTED WIRING BOARD ASSEMBLIES ........................................................................................ 16
»REPLACEMENT PARTS LIST ........................................................................................................... 19
»PACKING OF THE SET ..................................................................................................................... 25
Page
CONTENTS
SERVICE MANUAL
MODEL
POWER INPUT ....................................... 110-220 V AC 50/60 Hz
POWER RATING ....................................................................63 W
PICTURE SIZE ............................................. 580cm2(89.8sq inch)
CONVERGENCE............................................................. Magnetic
SWEEP DEFLECTION .....................................................Magnetic
FOCUS ............................................... Hi-Bi-Potential Electrostatic
INTERMEDIATE FREQUENCIES
Picture IF Carrier Frequency ..................................... 45.75 MHz
Sound IF Carrier Frequency ...................................... 41.25 MHz
Color Sub-Carrier Frequency..................................... 42.17 MHz
(Nominal)
AUDIO POWER
OUTPUT RATING.................................1.3W (at 10% distortion)
ELECTRICAL SPECIFICATIONS
SPEAKER
SIZE .............................................................................. 9 x 5 cm
VOICE COIL IMPEDANCE.............................16 ohm at 400 Hz
ANTENNA INPUT IMPEDANCE
VHF/UHF ....................................................75 ohm Unbalanced
TUNING RANGES
VHF-Channels .............................................................. 2 thru 13
UHF-Channels ............................................................ 14 thru 69
CATV Channels .......................................................... 1 thru 125
Specifications are subject to change without
prior notice.
SHARP CORPORATION
14LK20A

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14LK20A
IMPORTANT SERVICE SAFETY PRECAUTION
ËServiceworkshouldbe performed only by qualifiedservicetechnicianswhoare thoroughly
familiar with all safety checks and the servicing guidelines which follow:
X-RADIATION AND HIGH VOLTAGE LIMITS
1. Be sure all service personnel are aware of the
proceduresand instructions covering X-radiation.The
only potential source of X-ray in current solid state
TVreceivers is the picture tube.However, thepicture
tube does not emit measurable X-Ray radiation, if
the high voltage is as specified in the "High Voltage
Check" instructions.
It is only when high voltage is excessive that X-
radiation is capable of penetrating the shell of the
picture tube including the lead in the glass material.
The important precaution is to keep the high voltage
below the maximum level specified.
2. It is essential that servicemen have available at all
times an accurate high voltage meter.
The calibration of this meter should be checked
periodically.
3. Highvoltage should always be kept at therated value
−no higher. Operation at higher voltages may cause
a failure of the picture tube or high voltage circuitry
and;also, under certain conditions, may produce
radiation in exceeding of desirable levels.
4. Whenthehighvoltage regulator is operating properly
thereis no possibility of an X-radiation problem.Every
timeacolor chassis is serviced, the brightness should
be tested while monitoring the high voltage with a
meter to be certain that the high voltage does not
exceed the specified value and that it is regulating
correctly.
5. Do not use a picture tube other than that specified or
make unrecommended circuit modifications to the
high voltage circuitry.
6. Whentroubleshootingandtakingtestmeasurements
ona receiver with excessive high voltage, avoidbeing
unnecessarily close to the receiver.
Do not operate the receiver longer than is necessary
to locate the cause of excessive voltage.
WARNING
1. For continued safety, no modification of any circuit
should be attempted.
2. Disconnect AC power before servicing.
3. Semiconductor heat sinks are potential shock
hazards when the chassis is operating.
4. The chassis in this receiver has two ground systems
whichare separated by insulatingmaterial. The non-
isolated (hot) ground system is for the B+ voltage
regulatorcircuit and the horizontal outputcircuit. The
isolatedgroundsystemisforthelowB+ DCvoltages
and the secondary circuit of the high voltage
transformer.
To prevent electrical shock use an isolation
transformer between the line cord and power
receptacle, when servicing this chassis.
SERVICING OF HIGH VOLTAGE SYSTEM
AND PICTURE TUBE
When servicing the high voltage system,
remove the static charge by connecting a
10k ohm resistor in series with an insulated
wire (such as a test probe) between the pic-
ture tube ground and the anode lead. (AC
line cord should be disconnected from AC
outlet.)
1. Picture tube in this receiver employs integral
implosion protection.
2. Replace with tube of the same type number for
continued safety.
3. Do not lift picture tube by the neck.
4. Handle the picture tube only when wearing
shatterproof goggles and after discharging the high
voltage anode completely.

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14LK20A
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SAFETY NOTICE
Many electrical and mechanical parts in television
receivers have special safety-related characteristics.
These characteristics are often not evident from visual
inspection, nor can protection afforded by them be
necessarilyincreased by using replacement components
rated for higher voltage, wattage, etc.
Replacement parts which have these special safety
characteristics are identified in this manual; electrical
components having such features are identified by "å"
and shaded areas in the Replacement Parts Lists and
Schematic Diagrams.
IMPORTANT SERVICE SAFETY PRECAUTION
(Continued)
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. Inspect all protective devices such as non-metallic
control knobs, insulating materials, cabinet backs,
adjustment and compartment covers or shields,
isolation resistor-capacity networks, mechanical
insulators and etc.
3. To be sure that no shock hazard exists, check for
leakage current in the following manner.
•PlugtheACcorddirectlyintoa 110~120 voltACoutlet,
(Do not use an isolation transformer for this test).
•Using two clip leads, connect a 1.5k ohm, 10 watt
resistorparalleled by a 0.15µF capacitor in series with
all exposed metal cabinet parts and a known earth
ground,suchaselectricalconduitorelectricalground
connected to earth ground.
•Use anAC voltmeter having with 5000 ohm per volt,
or higher, sensitivity to measure theAC voltage drop
across the resistor. 1.5k ohm
10W
0.15µF
TEST PROBE
TO EXPOSED
METAL PARTS CONNECT TO
KNOWN EARTH
GROUND
For continued protection, replacement parts must be
identical to those used in the original circuit. The use of
substitutereplacement parts which do not have thesame
safety characteristics as the factory recommended
replacement parts shown in this service manual, may
create shock, fire, X-radiation or other hazards.
BEFORE RETURNING THE RECEIVER
(Fire & Shock Hazard)
Before returning the receiver to the user, perform
the following safety checks.
•Connect the resistor connection to all exposed metal
parts having a return to the chassis (antenna, metal
cabinet, screw heads, knobs and control shafts,
escutcheon and etc.) and measure the AC voltage
drop across the resistor.
AII checks must be repeated with the AC ine cord
plug connection reversed. (If necessary, a non-
polarized adapter plug must be used only for the
purpose of completing these check.)
Anycurrent measured must not exceed0.5 milliamp.
Any measurements not within the limits outlined
above indicate of a potential shock hazard and
corrective action must be taken before returning the
instrument to the customer.

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14LK20A
LOCATION OF USER'S CONTROL

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14LK20A
CIRCUIT PROTECTION
The receiver is protected by a 3.15A fuse (F701),
mounted on PWB-A, wired into one side of the AC
line input.
+115V DC REGULATOR ADJUSTMENT
The + 115V DC Adj. control (R721) is adjusted at the
factory. However, should readjustment be required
proceed as follows.
1. Actuate the receiver with 220V AC input voltage.
2. Receive a local channel.
3. Connect positive lead of digital voltmeter to R603
TP751 (positive side) on PWB-A; negative lead to
chassis ground.
4. Adjust R721 to obtain a +115V DC reading.
CAUTION: The reading should be within +115 ± 1V DC
to ensure normal function and circuitry
reliability.
X-RADIATION PROTECTOR CIRCUIT TEST
After service has been performed on the horizontal
deflection system, high voltage system, B+ system,
test the X-Radiation protection circuit to ascertain
proper operation as follows:
1. Apply 220V AC using a variac transformer for
accurate input voltage.
2. Allow for warm up and adjust all customer controls
for normal picture and sound.
3. Receive a good local channel.
4. Connect a digital voltmeter to TP653 and make sure
that the voltmeter reads 20.6 ± 1.5 V.
5. Apply external 26.8V DC at TP653 by using an
external DC supply, TV must be shut off.
6. To reset the protector, unplug the AC cord and make
ashortcircuitbetweenTP651 andTP652.Nowmake
sure that normal picture appears on the screen.
7. If the operation of the horizontal oscillator does not
stop in step 5, the circuit must be repaired before the
set is returned to the customer.
HIGH VOLTAGE CHECK
High voltage is not adjustable but must be checked
to verify that the receiver is operating within safe
and efficient design limitations as specified checks
should be as follows:
1. Connect an accurate high voltage meter between
ground and anode of picture tube.
2. Operatereceiverfor at least 15 minutesat 110~220V
AC line voltage, with a strong air signal or a properly
tuned in test signal.
3. Enter the service mode and select the service
adjustment "S19" and Bus data "01" (Y-mute on).
4. Thevoltageshouldbe approximately,24.0kV(atzero
beam).
Ifa correct readingcannotbeobtained,checkcircuitry
formalfunctioningcomponents.Afterthe voltage test,
make Y-mute off to the normal mode.
INSTALLATION AND SERVICE INSTRUCTIONS
Note: (1)When performing any adjustments to resistor controls and transformers use non-metallic
screwdrivers or TV alignment tools.
(2)Before performing adjustments, the TV set must be on at least 15 minutes.

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14LK20A
For adjustments of this model, the bus data is converted to various analog signals by the D/A converter
circuit.
Note: There are still a few analog adjustments in this series such as focus and master screen voltage.
Follow the steps below whenever the service adjustment is required. See "Table-B" to determine, if serv-
ice adjustments are required.
1. Service mode
Before putting unit into the service mode, check that
customer adjustments are in the normal mode. Use
the reset function in the video adjustment menu to
ensure customer controls are in their proper (reset)
position.
2. Service number selection
Once in the service mode, press the Ch-up or Ch-
down button on the remote controller or at the set.
The service adjustment number will vary in
increments of one, from "S01" to "M05". Select the
item you wish to adjust.
3. Data number selection
Press the Vol-up or down button to adjust the data
number.
To enter the service mode and exit serv-
ice mode.
While pressing the Vol-up and Ch-up buttons at the
sametime, plug the AC cord into a wall socket.
Now the TV set is switched on and enters the service
mode.
To exit the service mode, turn the television off by
pressing the power button.
0255S01
DATA NUMBER
(HEX )
(HEXADEC:MAL)
SERVICE ADJUSTMENT NUMBER
Figure A.
CHANNEL

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14LK20A
SERVICE
NUMBER DATA ADJUSTMENT CONTENTS
ADJUSTMENT ITEM RANGE
INITIAL VALUE
S01 PICTURE 55 00-7F
S02 TINT 46 00-7F
S03 COLOR 32 00-7F
S04 BRIGHTNESS 40 00-7F
S05 SHARPNESS 28 00-3F Must be set to "24"
S06 VERTICAL PHASE 00 00-07 Must be set to between "0" and "03"
S07 HORIZONTAL PHASE 12 00-1F
S08 RF-AGC 2A 00-3F
S09 VERTICAL AMP 20 00-3F
S10 VCO 2C 00-7F
S11 R CUT-OFF 00 00-FF
S12 G CUT -OFF 00 00-FF
S13 B CUT-OFF 00 00-FF
S14 G GAIN 7F 00-FF
S15 B GAIN 7F 00-FF
S16 TRAP(3.58MHz) 00 00 or 01 Must be set to "00"
S17 BALANCE 20 00-3F Must be set to "20"
S18 C.C.POSITION 18 00-7F
S19 Y-MUTE 00 00,01,03 00=NORMAL, 01=No Y, 03=No VERTICAL
OP OPTION 80 00-FF Must be set to "08"
M01 MTS LEVEL 0A 00-0F
M02 STEREO-VCO 20 00-3F
M03 FILTER 1C 00-3F
M04 LOW SEPARATION 20 00-3F
M05 HIGH SEPARATION 1B 00-3F
IC2001
IC2101 X
CRT X
IC201
Data is stored in IC2101.
Adjust items related to picture tube only.
Table - A
Holdingdown both the Ch-up/downbuttons ontheTV setat servicemodefor more than 2seconds willautomatically
write the above initial values into IC2101.
Table - B
The adjustment is needed to compensate for characteristics
of parts including IC201.
Holding down both the Ch-up/down bottons on the TV set in
the service mode for more than 2 seconds will automatically
write the above initial values into IC2101.
X
X
ADJUSTMENT
NECESSARY UNNECESSARY
PART REPLACED NOTES

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14LK20A
SERVICE ADJUSTMENT
VCO Adjustment
1. Connectadigital voltmeter between pin (44) of IC201
and ground.
2. Select a good local channel.
3. Enter the service mode and select the service
adjustment "S10".
4. Adjust the data so that digital voltmeter reads 2.2V.
5. Adjustment is completed, remove the voltmeter,
return to "normal" mode.
RF AGC Adjustment
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S08".
3. Set the data value to point where no noise or beat
appears.
4. Select another channel to confirm that no noise or
beat appears.
Note 1 : You will have to come out of the service
mode to select another channel.
Note 2 : Setting the data to"00" willproduce ablack
raster.
Screen Adjustment
1. Connect a digital voltmeter between TP852 and
TP853 on the CRT Unit.
Note: These test points may not be provided.
Then connect the voltmeter to both ends of
R852 located near Q852 on the foil side.
2. Receive a good local channel.
3. Enter the service mode and select the service
adjustment "S03" and set the data value to "00" to
set the color level to minimum (Record original data
code under adjustment "S03" before changing). You
may skip this step, if you selected a B/W picture or
monoscope pattern.
4. Select the service adjustment "S19" and adjust the
data value to "01", this turn off the luminance signal
(Y-mute).
5. Select the service adjustment "S04" and adjust data
value to obtain 0.17 volts on the digital voltmeter.
6. Adjust the master screen control until the raster
darkens to the point where raster is barely seen.
7. Adjusttheserviceadjustments"S11" red,"S12"green
and "S13" blue to obtain a good grey scale with
normal whites at low brightness level.
8. Select the service adjustment "S19" and reset data
to"00".Selecttheserviceadjustment"S03"andreset
data to obtain normal color level.
9. Removedigitalvoltmeter,andresetthemaster screen
control to obtain normal brightness range.
White Balance Adjustment
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S03" and set to "00" (minimum color).
"S03" does not have to be adjusted, if you selected a
B/W picture or monoscope pattern.
3. Alternatelyadjusttheservice adjustmentdataof"S14"
and "S15" until a good grey scale with normal whites
is obtained.
4. Select the service adjustment "S03" and adjust data
to obtain normal color level.
Sub-Picture Adjustment
1. Receive a good local channel.
2. Make sure the customer picture control is set to
maximum.
3. Enter the service mode and select the service
adjustment "S01".
4. Adjust the data value to achieve normal contrast
range.
Sub-Tint Adjustment
1. Receive a good local channel.
2. Set customer tint control to center of it's range.
3. Enter the service mode and select the service
adjustment "S02".
4. Adjust "S02" data value to obtain normal flesh tones.
Sub-Color Adjustment
1. Receive a good local channel.
2. Makesure the customer color controlis settocenter
position .
3. Enter the service mode and select the service
adjustment "S03".
4. Adjust "S03" data value to obtain normal color level.

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14LK20A
Sub-Brightness Adjustment
1. Receive a good local channel.
2. Make sure the customer brightness control is set to
center position.
3. Enter the service mode and select the service
adjustment "S04".
4. Adjust "S04" data value to obtain normal brightness
level.
Vertical-Size Adjustment
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S09".
3. While observing the top and bottom of the screen,
adjust "S09" data value to proper vertical size.
Vertical Phase Adjustment
1. Enter the service mode and select the service
adjustment "S06".
2. Adjust data value to "00"~"03" so that picture is
approximate center.
Note: This must be set "00"~"03" when adjust
another data retrace line will be appear.
Horizontal Position Adjustment
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S07".
3. Adjust "S07" data value so that picture is centered.
Caption Position Adjustment (Horizontal)
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S18".
3. A black text box appears on the screen. (see Figure
B. below)
4. Adjust "S18" data value so that text box is positioned
in the center of the screen.
Figure B.
3.58MHz Trap Adjustment
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustment "S16".
3. This is a two position adjustment, "00" is ON, "01" is
OFF.
4. Adjust data value to "00" for normal viewing.
Sharpness and Audio Balance Adjust-
ments
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustments"S05" for sharpness and "S17"for audio
balance.
»Sharpness Adjustment
3. Adjust data value to "24" (center of data range) for
sharpness adjustment.
»Audio Balance Adjustment
4. Adjust data value to "20" (center of data range) for
Audio balance adjustment.

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14LK20A
CHASSIS LAYOUT
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14LK20A
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BLOCK DIAGRAM