Toshiba 20AR20, 20AR30 Service Manual
20AR20/30
SERVICE MANUAL
COLOR TELEVISION
Chassis No. SN-70A
20AR20
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.
20AR30
MODELS
20AR20/30
CONTENTS
Page
ELECTRICAL SPECIFICATIONS.........................................................................................................
IMPORTANT SERVICE SAFETY PRECAUTION ................................................................................
LOCATION OF USER'S CONTROL ....................................................................................................
INSTALLATION AND SERVICE INSTRUCTIONS ...............................................................................
CHASSIS LAYOUT .............................................................................................................................
BLOCK DIAGRAM .............................................................................................................................
SCHEMATIC DIAGRAMS ..................................................................................................................
PRINTED WIRING BOARD ASSEMBLIES ........................................................................................
REPLACEMENT PARTS LIST ...........................................................................................................
P
ACKING OF THE SET ..................................................................................................................... 31
1
2
4
5
11
13
15
22
25
ELECTRICAL SPECIFICATIONS
POWER INPUT ......................................... 110-220 V AC 50/60 Hz
POWER RATING
20AR20....
20AR30................................................................................. 98 W
PICTURE SIZE ........................................... 1,194cm2 (185sq inch)
CONVERGENCE ............................................................. Magnetic
SWEEP DEFLECTION .....................................................Magnetic
FOCUS ...............................................
INTERMEDIATE FREQUENCIES
Picture IF Carrier Frequency ..................................... 45.75 MHz
Sound IF Carrier Frequency ...................................... 41.25 MHz
Color Sub-Carrier Frequency ..................................... 42.17 MHz
AUDIO POWER
OUTPUT RATING
20AR20................................................ 1.3W (at 10% distortion)
20AR30................................................ 2.5W (at 10% distortion)
............................................................................. 88 W
...............
QPF Electrostatic
(Nominal)
SPEAKER
SIZE ........................................................................ 9 cm x 5 cm
VOICE COIL IMPEDANCE
20AR20........................................................... 8 ohm at 400 Hz
20AR30......................................................... 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.
1
1
20AR20/30
IMPORTANT SERVICE SAFETY PRECAUTION
Service work should be performed only by qualified service technicians who are throughly
familiar with all safety checks and the servicing guidelines which follow:
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
which are separated by insulating material. The nonisolated (hot) ground system is for the B+ voltage
regulator circuit and the horizontal output circuit. The
isolated ground system is for the low 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 VOLT AGE 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 picture 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.
X-RADIATION AND 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 Xradiation 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 voltage should always be kept at the rated 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. When the high voltage regulator is operating properly
there is no possibility of an X-radiation problem. Every
time a color 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. When trouble shooting and taking test measurements
on a receiver with excessive high voltage, avoid being
unnecessarily close to the receiver.
Do not operate the receiver longer than is necessary
to locate the cause of excessive voltage.
2
IMPORTANT SERVICE SAFETY PRECAUTION
(Continued)
20AR20/30
BEFORE RETURNING THE RECEIVER
(Fire & Shock Hazard)
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. 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, 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 110~220 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 0.15 F 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 an AC voltmeter having with 5000 ohm per volt,
or higher, sensitivity to measure the AC voltage drop
across the resistor.
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
Line
cord
plug connection reversed. (If necessary , a nonpolarized adapter plug must be used only for the
purpose of completing these check.)
Any current 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.
AC
VOLTMETER
1.5k ohm
10W
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 " "
and shaded areas in the Replacement Parts Lists and
Schematic Diagrams.
!
0.15 F
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
substitute replacement parts which do not have the same
safety characteristics as the factory recommended
replacement parts shown in this service manual, may
create shock, fire, X-radiation or other hazards.
3
20AR20/20AR30
Front Panel
20AR20 20AR30
Location of Controls
CHANNEL UP/DOWN
POWER
Press On.
Press again Off.
SENSOR
AREA FOR
REMOTE CONTROL
( ) Selects next higher channel.
( ) Selects next lower channel.
VOLUME UP/DOWN
(+) Increases sound.
(–) Decreases sound.
Basic Remote Control Functions
POWER
Press On.
Press again Off.
REMOTE KEYPAD
Accesses any channel from keypad.
RETURN
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.
VIDEO/AUDIOIN TERMINALS
POWER
Press On.
Press again Off.
SENSOR
AREA FOR
REMOTE CONTROL
VIDEO/AUDIOIN TERMINALS
CHANNEL UP/DOWN
( ) Selects next higher channel.
( ) Selects next lower channel.
VOLUME UP/DOWN
(+) Increases sound.
(–) Decreases sound.
Infrared Transmitter Window
INPUT
Press Switch to external video input
mode.
Press again Switch to TV mode.
See page
17.
CHANNEL UP/DOWN
( ) Selects next higher channel.
( ) Selects next lower channel.
• See pages
15, 16 for channel
presetting.
• Moves the “ ” mark of the MENU
screen.
MENU
Press Accesses MAIN MENU.
Press again Exits MAIN MENU.
DISPLAY
Press Displays receiving channel for
4 seconds.
Press again Removes display.
• Temporarily displays receiving
channel when in Closed Caption
mode.
CT-818
4
20AR20/30
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.
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.
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 ± 1.5V.
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
a short circuit between TP651 and TP652. 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 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. The voltage should be approximately, 26.5kV (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.
5
20AR20/30
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 service 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 Chdown 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.
DATA NUMBER
(HEX)
SERVICE ADJUSTMENT NUMBER
To enter and exit service mode.
While pressing the Vol-up and Ch-up buttons at the
sametime, plug the AC cord into a wall socket.
The TV is now switched on and enters service mode.
To exit the service mode, turn the television off by
pressing the power button.
CHANNEL
S01
Figure A.
55
02
S01 D:00
6
20AR20/30
SERVICE
NUMBER
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 between "0" to "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 / V-MUTE 00 00,01,03 "00"=Normal, "01"=No-Y, "03"=No Vertical
OP. OPTION (Set to each model) 80 00-FF Must be set to "08"=20AR20, "09"=20AR30
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
ADJUSTMENT ITEM
INITIAL VALUE
DATA
ADJUSTMENT CONTENTS
RANGE
Table - A
Holding down both the CH-up/down buttons on the TV set at service mode for more than 2 seconds will automatically
write the above initial values into IC2101.
PART REPLACED
IC2001
IC201 X
IC2101
CRT
IC3001
(20AR30)
ADJUSTMENT
NECESSARY
X
X
X
UNNECESSARY
X
Data is stored in IC2101.
The adjustment is needed to compensate for characteristics
of parts including IC201.
Holding down both the CH-up/down buttons on the TV set in
the service mode for more than 2 seconds will automatically
write the above initial values into IC2101.
Adjust items related to picture tube only.
Adjust items related to MTS only (M01~M05).
NOTES
Table - B
7
20AR20/30
SERVICE ADJUSTMENT
VCO Adjustment
1. Connect a digital voltmeter between pin (44) of IC201
and ground.
2. Receive 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" will produce a black
raster.
Screen Adjustment
1. Connect a digital voltmeter between TP852 and
TP853 on the CRT socket PWB.
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 oscilloscope screen.
6. Adjust the master screen control until the raster
darkens to the point where raster is barely seen.
7. Adjust the service adjustments "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". Select the service adjustment "S03" and reset
data to obtain normal color level.
9. Remove digital voltmeter, and reset the master 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. Alternately adjust the service adjustment data of "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.
+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. Select 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 +115V –1VDC
to ensure normal function and circuitry
reliability.
8
20AR20/30
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 "S03".
4. Adjust "S03" 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 "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.
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 Adjustments
1. Receive a good local channel.
2. Enter the service mode and select the service
adjustments "S05" for sharpness and "S17" for
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.
Figure B.
9
20AR20/30
MTS ADJUSTMENT
(Only for 20AR30)
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.
Spec.: 490 –10mVrms.
MTS VCO Adjustment
1. Keep the unit in no-signal state.
2. Connect the 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.
Spec.: 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 8 again for fine
adjustment.
10
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