Sharp 20LK61M User manual

1
20LK31M
20LK61M
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.
S80G420LK31M/
»ELECTRICAL SPECIFICATIONS.........................................................................................................1
»IMPORTANT SERVICE SAFETY PRECAUTION ................................................................................2
»LOCATION OF USER'S CONTROL.....................................................................................................4
»INSTALLATION AND SERVICE INSTRUCTIONS ...............................................................................5
»CHASSIS LAYOUT.............................................................................................................................10
»BLOCK DIAGRAM..............................................................................................................................12
»SCHEMATIC DIAGRAMS...................................................................................................................14
»PRINTED WIRING BOARD ASSEMBLIES........................................................................................21
»REPLACEMENT PARTS LIST ...........................................................................................................24
»PACKING OF THE SET......................................................................................................................31
Page
CONTENTS
ELECTRICAL SPECIFICATIONS
Specifications are subject to change without
prior notice.
SERVICE MANUAL
20LK31M
20LK61M
SHARP CORPORATION
MODELS
20LK61M
20LK31M
POWER INPUT ........................................110-220 V AC 50/60 Hz
POWER RATING
20LK31M............................................................................ 88 W
20LK61M............................................................................ 98 W
PICTURE SIZE .......................................... 1,194cm2(185sq 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
20LK31M........................................... 1.5W (at 10% distortion)
20LK61M........................................... 3.0W (at 10% distortion)
SPEAKER
SIZE ........................................................................9 cm ×5 cm
VOICE COIL IMPEDANCE
20LK31M ...................................................16 ohm at 400 Hz
20LK61M ...................................................32 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
LK
LK

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20LK31M
20LK61M
IMPORTANT SERVICE SAFETY PRECAUTION
ËService work should be performed only by qualified service technicians who are throughly
familiar with all safety checks and the servicing guidelines which follow:
X-RADIATIONAND HIGH VOLTAGE LIMITS
1. Be sure all service personnel are aware of the
procedures and instructions covering X-radiation.
The only potential source of X-ray in current solid
state TV receivers is the picture tube. However, the
picture 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. High voltageshouldalways bekeptat theratedvalue
-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. When thehighvoltage regulatorisoperating properly
there is no possibility of an X-radiation problem.
Everytime acolor chassisisserviced,the brightness
should be tested while monitoring the high voltage
with a meter to be certain that the high voltage does
notexceed thespecifiedvalue andthatit isregulating
correctly.
5. Do not use a picture tube other than that specified
ormakeunrecommended circuit modifications to the
high voltage circuitry.
6. When trouble shooting and taking test
measurements on a receiver with excessive high
voltage, avoid being unnecessarily close to the
receiver.
Donotoperatethereceiverlongerthanisnecessary
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. Thechassisinthisreceiverhas two ground systems
whichare separated by insulating material.The non-
isolated (hot) ground system is for the B+ voltage
regulatorcircuit and the horizontal outputcircuit.The
isolatedground system is for thelow B+ DC voltages
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, re-
move the static charge by connecting a 10k
ohm resistor in series with an insulated wire
(such as a test probe) between the picture
tubegroundandtheanode lead.(AClinecord
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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20LK61M
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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
necessarily increased 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.
»Plug the AC cord directly into a 120 volt AC outlet,
(Do not use an isolation transformer for this test).
»Using two clip leads, connect a 1.5k ohm, 10 watt
resistor paralleled by a 0.15mF capacitor in series
with all exposed metal cabinet parts and a known
earth ground, such as electrical conduit or electrical
ground connected to earth ground.
»Use anAC voltmeter having with 5000 ohm per volt,
or higher, sensitivity to measure theAC voltage drop
across the resistor.
For continued protection, replacement parts must be
identical to those used in the original circuit. The use of
substitute replacement parts which do not have the
samesafety characteristicsasthe factoryrecommended
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.
»Connecttheresistor 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 line 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 exceed 0.5 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.
1.5k ohm
10W
0.15µF
TEST PROBE
CONNECT TO
KNOWN EARTH
GROUND
TO EXPOSED
METAL PARTS
AC
VOLTMETER

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LOCATION OF USER'S CONTROL
TV
InfraredTransmitter Window
INPUT
Press→Switch to external video input
mode.
Press again →Switch to TV mode.
CHANNEL UP/DOWN
() Selects next higher channel.
() Selects next lower channel.
• Moves the “ ” mark of the MENU
screen.
MENU
Press →Accesses MAIN MENU.
Press again →Exits MAIN MENU.
DISPLAY
Press→Displaysreceiving channel for
4 seconds.
Press again →Removes display.
• Temporarily displays receiving
channel when in Closed Caption
mode.
Front Panel
Basic Remote Control Functions
POWER
Press →On.
Press again →Off.
REMOTE KEYPAD
Accesses any channel from keypad.
FLASHBACK
Returns to previous channel.
VOLUME UP/DOWN
(+) Increases sound.
(–) Decreases sound.
• In menu mode, changes or selects
the TV adjustments.
MUTE
Press Mutes sound.
Press again →Restores sound.
• CLOSED CAPTION appears when
sound is muted.
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20LK61M20LK31M
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VIDEO/AUDIO-
IN TERMINALS
CHANNEL UP/DOWN
) Selects next higher channel.
) Selects next lower channel.
SENSOR AREA FOR
REMOTE CONTROL SENSOR AREA FOR REMOTE CONTROL
VOLUME UP/DOWN
(+) Increases sound.
(–) Decreases sound.
POWER
Press →On.
Press again →Off. (
(
VIDEO/AUDIO-
IN TERMINALS
CHANNEL UP/DOWN
) Selects next higher channel.
) Selects next lower channel.
VOLUME UP/DOWN
(+) Increases sound.
(–) Decreases sound.
POWER
Press →On.
Press again →Off. (
(

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20LK61M
CIRCUIT PROTECTION
The receiver is protected by a 4.0A fuse (F701),
mounted on PWB-A, wired into one side of the AC
line input.
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 120V 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 21.3 ±1.5V.
5. Apply external 27.2V DC at TP653 by using an
external DC supply, TV must be shut off.
6. To reset the protector, unplug theAC cord and make
ashort circuit betweenTP651 andTP652.Now make
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. Operate receiver for at least 15 minutes at 120VAC
line voltage, with a strong air signal or a properly
tuned in test signal.
3. Enter the service mode and select the service
adjustment "S03" and Bus data "01" (Y-mute on).
4. The voltageshould be approximately, 26.0kV(at zero
beam).
If a correct reading cannot be obtained, check
circuitry for malfunctioning components. After the
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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20LK61M
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 adjusment is required.
To enter the service mode and exit service 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.
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 control are in their proper (reset) position.
2. Service number selection.
In the service mode, you will see the window screen as window 1. There are 3 adjustment categories 2DEF,
3SIGNAL, 4FIX VALUE as show in Figure A.
Press CH UP/DOWN button for selection and enter by VOL UP or VOL DOWN.
Press CH UP/DOWN button to select the adjustment item and VOL UP/DOWN
to adjust the data number for each categories.
(OSD disturbance can be erased by R/C display key)
(Note: EEPROM – factory used only)
Figure A: Adjustment Categories
Window 2: DEF
DEF
RETURN
FIX VALUE
NEXT
RETURN
D01
D03
D05
RETURN
D02
D04
D06
Window 4: FIXVALUE
Window 1: ADJUSTMENT Categories
SERVICE MODE
DEF
SIGNAL
FIX VALUE
EEPROM
RETURN
Window 3: SIGNAL
SIGNAL S01
S13
RETURN
S02
S12
F01 F02
F13 F14
RETURN NEXT
F15 F16
F25 F26
RETURNPREVIOUS
PREVIOUS

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20LK31M
20LK61M
Below are the adjustments ranges and initial values for FIX VALUE category.
FIX VALUE
F01 OPTION 1 00-FF B0 A0
F02 OPTION 2 00-FF 04 0C
F03 E-SAVE 00-3F 23 1F
F04 TUNER SETUP 00, 01 00 00
F05 R-TONE RD 00-7F 19 03
F06 R-TONE BD 00-7F 00 7C
F07 B-TONE RD 00-7F 00 00
F08 B-TONE BD 00-7F 12 04
F09 FM LEVEL 00-1F 0C 0C
F10 AFC GAIN 00, 01 00 00
F11 G DRIVE 00, 0F 00 0F
F12 FBT BLK SW 00,01 01 01
F13 V COMP 00-07 07 07
SERVICE
POSITION ADJUST ITEM DATA
RANGE
INITIAL VALUE (Hex)
Table - A
Below are the ranges and initial values for each adjustment and in each categories.
DEF
D01 H-PHASE 00-1F 0C
D02 V-SIZE 00-7F 40
D03 V-POSITION 00-3F 20 Must be "20"
D04 CC-POSITION 00-FF 1A
D05 V-LINEARITY 00-1F 10 Must be "12"
D06 V-S-CORRECTION 00-1F 10 Must be "0F"
SERVICE
POSITION ADJUST ITEM DATA
RANGE
INITIAL VALUE
ADJUSTMENT CONTENTS
Table - B
SIGNAL
Note: Refer to the SERVICE ADJUSTMENT for each corresponding values.
Table - C
S01 RF AGC 00-3F 14
S02 VIDEO LEVEL 00-07 03
S03 Y-MUTE 00-03 00
"01":Y-MUTE, "02":V-STOP&Y-MUTE
"03":Activate color killer circuit
S04 SUB BIAS 00-FF 40 Must be "30"
S05 R-BIAS 00-FF 00
S06 G-BIAS 00-FF 00
S07 B-BIAS 00-7F 00
S08 R-DRIVE 00-7F 40
S09 B-DRIVE 00-7F 40
S10 CONTRAST 00-7F 5A
S11 TINT 00-7F 40
S12 COLOR 00-7F 40
S13 BRIGHTNESS 00-7F 40
SERVICE
POSITION ADJUST ITEM DATA
RANGE
INITIAL VALUE
ADJUSTMENT CONTENTS
Holding down both the Vol-up/Ch-down buttons on the TV set at service mode for more than 2 seconds will
automatically write the above initial values into IC2101.
IC2001
IC2101 X
CRT X
IC201
Data is stored in IC2101.
Adjust items related to picture tube only.
Table - D
The adjustment is needed to compensate for characteristics
of parts including IC201.
Holding down both the Vol-up/Ch-down buttons 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
F14 OSD CONT 00-03 02 01
F15 SHARPNESS 00-3F 19 19
F16 FLT SYS 00-07 00 00
F17 KILLER OP 00-07 04 02
F18 PRE SHOOT 00-03 03 00
F19 CORING 00-03 04 04
F20 DC REST 00-03 02 02
F21 BS START 00-03 01 01
F22 BS GAIN 00-03 01 01
F23 ABL START 00-07 00 00
F24 R/B ANGLE 00-0F 08 08
F25 H BLK R 00-0F 04 03
F26 H BLK L 00-0F 04 06
SERVICE
POSITION ADJUST ITEM DATA
RANGE
INITIAL VALUE (Hex)

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White Balance Adjustment.
1. Receive a good local channel.
2. Selecttheservice adjustment "S12" and set the data
value to "00" to set the color level to the minimun.
You may skip this step, if you selected a B/W picture
or monoscope.
3. Alternately adjust the service adjustment data of
"S08" and "S09" until a good grey scale with normal
white is obtained.
4. Select the service adjustment "S12" and reset 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 "S10".
4. Adjust the data value to achieve normal contrast
range.
Sub-Tint Adjustment
1. Receive a good local channel.
2. Set thecustomer tintcontrol tothecenter ofit’srange.
3. Enter the service mode and select the service
adjustment "S11".
4. Adjust "S11"datavalueto obtain normal fresh tones.
Sub-Color Adjustment
1. Receive a good local channel.
2. Make sure the customer color control is set to center
position.
3. Enter the service mode and select the service
adjustment "S12".
4. Adjust "S12" data value to obtain normal color level.
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 "S13".
4. Adjust "S13" data value to obtain normal brightness
level.
Figure B: Waveform for Screen Adjustment
ËSERVICE ADJUSTMENT
RF AGC Adjustment
1. Receive a good local channel.
2. Enter the service mode signal category and select
the service adjustment "S01".
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: You have to exit the service mode first to
select another channel.
Video Level (TV Det Video Level)
Adjustment
1. Receive a good local channel.
2. Enter the service mode signal category and select
the service adjustment "S02".
3. Set the data value to "02" first, then adjust the data
inranges 02 ±2step to obtainanormal contrast level.
Screen Adjustment
1. Connect to oscilloscope probe between TP855 and
ground of the CRT unit.
2. Receive a good local channel.
3. Enter the service mode Signal category and set the
service adjustment "S04" to step 30. Then select the
service adjustment "S12" and set the data value to
"00" to set the color level to the minimum level.
(recordthe original data first).Youmay skip this step,
if you selected a B/W picture or monoscope pattern.
Set also the "S05/S06/S07" data to minimum level.
4. Selecttheservice adjustment "S03" and set the data
valueto "01"to turn offtheluminance signal (Y-mute).
5. Select the service adjustment "S13" and adjust the
data value to obtain 2.35 volts as shown in Figure B.
6. Adjust the master screen control until the raster
darkens to the point where raster is barely seen.
7. Adjust theserviceadjustment "S05" red, "S06"green
and "S07" blue to obtain a good grey scale with
normal white at low brightness level.
8. Select the serviceaadjustment "S03" and reset data
to"00". Selectthe service adjustment"S12" andreset
data to obtain normal color level.
9. Remove probe and reset the master screen control
to obtain normal brightness range.
2.35Vdc
GND

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20LK61M
ËMTS ADJUSTMENT
MTS Level Adjustment
1. Feed the following monaural signal to pin (14) of
IC3001.
Monaural signal: 300Hz, 245mVrms
2. Connect the rms voltmeter to pin (39) of IC3001.
3. Enter the service mode and select the service
adjustment "M01".
4. Adjust the data so that the rms voltmeter reads 490
±10mVrms.
MTS VCO Adjustment
1. Keep the unit in no-signal state.
2. Connectthe frequency counter to pin(39) of IC3001.
3. Connect a capacitor (100µF, 50V) in between
positive(+) side of C3005 and ground.
4. Enter the service mode and select the service
adjustment "M02"
5. Adjust the data so that the frequency counter reads
62.94 ±0.75kHz.
Filter Adjustment
1. Feed the following stereo pilot signal to pin (14) of
IC3001 .
Stereo pilot signal: 9.4kHz, 600mVrms.
2. Enter the service mode and select the service
adjustment "M03".
3. Adjust the data at the point where "OK" appears on
the screen. The "OK" represents the approximate
center of the adjustable range of the data.
Separation Adjustment
1. Connect the rms voltmeter to pin (39) of IC3001.
2. Receive the following composite stereo signal 1.
Composite stereo signal: 30% modulation, left
channel only, noise reduction on, 300Hz
3. Enter the service mode and select the service
adjustment "M04".
4. Adjust the data until the AC voltage reading of the
rms voltmeter is minimum.
5. Receive the following composite stereo signal 2.
Stereo signal: 30% modulation, left channel only,
noise reduction on, 3kHz
6. Enter the service mode and select the service
adjustment "M05".
7. Adjust the data until the AC voltage reading of the
rms voltmeter is minimum.
8. Take the above steps 1 thru 7 again for fine
adjustment.
Vertical-Size, V-Linearity and
V-S Correction Adjustments
1. Receive a good local channel.
2. Enter the service mode DEF category and select the
adjustment "D02" for Vertical Size, "D05" for V-
Linearity and "D06" for V-S Correction Adjustment.
3. Set in order "D05" for V-Linearity, "D06" for V-S
Correction and set the data to get the best linearity.
4. Then adjust "D02" data unitl it become a proper
vertical size.
Horizontal Position Adjustment
1. Receive a good local channel.
2. Enter the service mode DEF category and select the
adjustment "D01".
3. Adjust "D01" data value to center the picture.
Vertical-Phase Adjustment
1. Receive a good local channel.
2. Enter the service mode DEF category and select the
adjustment "D03".
3. Adjust "D03" bus data to get the most acceptable
vertical position.
Note: The step range is 20 (032) ±10 steps.
Caption Position Adjustment (Horizontal)
1. Receive a good local channel.
2. Enter the service mode DEF category and select the
adjustment "D04".
3. Ablacktextbox willappearon thescreen.(seeFigure
C. below)
4. Adjust "D04" data value to balance the text box
position in the center. (A=B).
Figure C.
A B

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MODEL 20LK31M CHASSIS LAYOUT
PWB-A
PWB-B
PWB-C

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MODEL 20LK61M CHASSIS LAYOUT
PWB-A
PWB-B
PWB-C

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MODEL 20LK31M BLOCK DIAGRAM

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MODEL 20LK61M BLOCK DIAGRAM

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DESCRIPTION OF SCHEMATIC DIAGRAM
NOTES:
1. The unit of resistance "ohm" is omitted.
(K=k Ω =1000 Ω , M=M Ω )
2. All resistors are 1/16 watt, unless otherwise noted.
3. All capacitors are µ F, unless otherwise noted.
(P=pF=µµF)
4. (G) indicates ±2% tolerance may be used.
5. indicates line isolated ground.
VOLTAGE MEASUREMENT CONDITIONS:
1. All DC voltages are measured with DVM connected
between points indicated and chassis ground, line
voltageset at120VACandall controlsset for normal
picture unless otherwise indicated.
2. All voltages measured with 1000µ V B & W or Color
signal.
WAVEFORM MEASUREMENT CONDITIONS:
1. Photographs taken on a standard gated color bar
signal, the tint setting adjusted for proper color. The
wave shapes at the red, green and blue cathodes of
the picture tube depend on the tint, color level and
picture control.
2. indicates waveform check points (See chart,
waveforms are measured from point indicated to
chassis ground.)
å AND SHADED ( ) COMPONENTS
= SAFETY RELATED PARTS.
' MARK= X-RAY RELATED PARTS.
This circuit diagram is a standard one, printed circuits
may be subject to change for product improvement
without prior notice.
WAVEFORMS

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SCHEMATIC DIAGRAM: CRT and FRONT AV Unit
Ë 20LK61M
Ë 20LK31M

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MODEL 20LK31M SCHEMATIC DIAGRAM: MAIN Unit

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MODEL 20LK61M SCHEMATIC DIAGRAM: MAIN-1 Unit

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MODEL 20LK61M SCHEMATIC DIAGRAM: MAIN-2 Unit

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PWB-C: FRONT AV Unit (Wiring Side)
PWB-B: CRT Unit (Wiring Side)
PRINTED WIRING BOARDASSEMBLIES

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PWB-A: MAIN Unit (Wiring Side)