Sharp 20CT-250 User manual

20CT-250
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.
The chassis in this receiver is partially hot. Use an isolation transformer between the line cord plug and power
receptacle, when servicing this chassis.
Topreventelectricshock,donotremovecover. Nouser–serviceablepartsinside. Referservicingtoqualified
service personnel.
WARNING
20CT-250
FEATURE
»SPECIFICATIONS...............................................2
»IMPORTANTSERVICE NOTES ......................... 2
»ADJUSTMENT PRECAUTIONS ........................ 3
»SERVICE ADJUSTMENT................................... 6
»TROUBLESHOOTINGTABLE......................... 15
»SOLID STATE DEVICE BASE DIAGRAM ........ 18
Page
CONTENTS
Page
SHARP CORPORATION
ËFull Auto Channel Preset And Auto Channel Skip
Ë100 CH Program Memory
ËAperture Control Circuit
ËBlack Stretch Circuit
ËBilingual System (Mono)
ËAuto Channel Scan System
ËFavorite Channel Memory System
COLOURTELEVISION
Chassis No. G2
SERVICE MANUAL
S88U521CT-250
»CHASSISLAYOUT............................................17
»SCHEMATIC DIAGRAM ................................... 19
»BLOCK DIAGRAM ............................................23
»PRINTED WIRING BOARD ASSEMBLIES ...... 25
»REPLACEMENT PARTS LIST.......................... 27
MODEL
ËUser Preset Timer (On Timer/Sleep Timer/Reminder)
Ë2 Selectable OSD Languages (English/Thai)
ËCATV (Hyper Band) Ready
〈Used Frequency Synthesizer Tuner〉
ËNTSC 4.43/3.58MHz (AV only), Rear AV IN/OUT
terminal
ËBlue Back Noise Mute
ËFine Tuning Adjustable with Remote Control

2
2-1 2-2
20CT-250
IMPORTANT SERVICE NOTES
Maintenance and repair of this receiver should be done by
qualified service personnel only.
SERVICING OF HIGH VOLTAGE SYSTEM AND
PICTURE TUBE
When servicing the high voltage system, remove static charge from it by
connecting a 10k ohm Resistor in series with an insulated wire (such as a
test probe) between picture tube dag and 2nd 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 completely
X-RAY
This receiver is designed so that any X-Ray radiation is kept to an absolute
minimum. Since certain malfunctions or servicing may produce potentially
hazardous radiation with prolonged exposure at close range, the following
precautions should be observed:
1. When repairing the circuit, be sure not to increase the high voltage to more than 24.5
kV (at beam 0 µA) for the set.
2. To keep the set in a normal operation, be sure to make it function on 22.0 kV ±1.5 kV (at
beam 800 µA) in the case of the set. The set has been factory –Adjusted to the above-
mentioned high voltage.
If there is a possibility that the high voltage fluctuates as a result of the repairs, never
forget to check for such high voltage after the work.
3. Do not substitute a picture tube with unauthorized types and/or brands which may cause
excess X-ray radiation.
BEFORE RETURNING THE RECEIVER
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 fishpapers,
cabinet backs, adjustment and compartment covers or shields, isolation resistor-
capacity networks, mechanical insulators etc.
SPECIFICATIONS
Convergence.................................................................... Self Converging System
Focus .........................................................................Uni Bi-Potential Electrostatic
Sweep Deflection ..................................................................................... Magnetic
Intermediate Frequencies
Picture IF Carrier ................................................................................. 38.9 MHz
Sound IF Carrier Frequency ...................................................... 33.16/33.4 MHz
Colour Sub-Carrier Frequency .............................................................. 34.47 MHz
PowerInput ........................................................................220-240V AC 50/60 Hz
Power Consumption ........................................................................................ 80W
Audio Power Output Rating ........................................................................... 3.0 W
(at Max.)
Speaker
Size .....................................................................................................10 cm pcs
Voice Coil Impedance..............................................................8 ohms at 400 Hz
Aerial Input Impedance
VHF/UHF.............................................................................75 ohm Unbalanced
Receiving System .............................................................CCiR SECAM/PAL B, G
NTSC 3.58/4.43 MHz (AV Input Only)
Tuner Ranges
»VHF-Channels ................................. E2 (48.25 MHz) thru E12 (224.25 MHz)
»UHF-Channels ............................. E21 (471.25 MHz) thru E69 (855.25 MHz)
Dimensions ................................................................................. Width: 690.0 mm
Height: 462.5 mm
Depth: 481.0 mm
Weight (approx.): 20.2 kg
Cabinet Material.................................................................................... All Plastics
Specifications are subject to change without prior notice.

3
3-1 3-2
20CT-250
ADJUSTMENT PRECAUTIONS
This model’s settings are adjusted in two different ways: through the I2C bus control and in the conventional analog
manner. The adjustment via the I2C bus control includes preset-only items and variable data.
1. Calling the service mode by the microprocessor
1Set the switch S1006 to the service mode position, and the microprocessor is put in the service mode
(adjustment through the I2C bus control).
2Press the CH UP/DOWN keys on the remote controller to select the modes one by one.
3Press the CH UP/DOWN keys on the remote controller to select the modes in the order opposite to the
above step 2.
4Using the VOLUME UP/DOWN keys on the remote controller, the data can be modified.
5Set the switch S1006 to the normal mode (OFF) position, and the microprocessor is put out of the
service mode.
2. Factory presettings
1Set the switch S1006 to the service mode position and turn on the main power switch. Initial values are
automatically preset only when a new E2PROM is used (judgment with the first 4 bytes).
2The initial data are preset as listed on page 5.
3Keep in mind that some settings should be modified, and the others should remain as preset.
Note: Once the chassis has been put together, be sure to set the switch S1006 to the service mode
position first and then turn on the main power switch (see the step 2.-1above). Turning on
the power without initializing the E2PROM may cause a flow of excess beam current.
3. The accompanying memory map (11-page document for the RH-iX3031CE ) is for your
reference.

4
4-1 4-2
20CT-250
User data
CONTRAST MAX (64/64)
COLOUR CENT (32/64)
BRIGHTNESS CENT (32/64)
TINT CENT (32/64)
SHARPNESS CENT (32/64)
S-VOLUME MIN (1/64)
BLUE BACK OFF
* When the modes are switched, the last service mode data are stored into the E2PROM.
* In the service mode, the user data are preset as follows.
Mode Key input
H-CENTER 50 PICTURE
V-CENTER 50 TEXT
V-AMP 50 INDEX
V S CORR 50 RED
V-LINE 50 GREEN
SUB CONT CANCEL
Y SUB CONT REVEAL
SUB COLOUR TIMEDPAGE
SUB BRIGHT SIZE
SUB TINT HOLD
SUB SHARP RESET
R-Y YELLOW
B-Y CYAN
A/V 1/2 SKIP
VIDEO MUTE BLUE BACK
* The following keys are used to go directly to their respective modes.
SERVICE MODE
(1) Press the specific keys to change the modes as follows.
In the direction of arrow : CH DOWN key
In the opposite direction : CH UP key
RASTER mode
R-CUT OFF
G-CUT OFF
B-CUT OFF
KEY
R-CUT OFF
G-CUT OFF
B-CUT OFF
R-DRIVE
B-DRIVE
LATERAL mode
V-AMP 50 Hz (V-AMP50)
V-LINE 50 Hz (V-LINE50)
S-CORRECT 50 Hz (V S-CORR50)
V-PHASE 50 Hz (V-CENTER50)
H-PHASE 50 Hz (H-CENTER50)
V-BLK START (V-BLK ST50)
V-BLK STOP (V-BLK SP50)
UP
1 KEY
2 KEY
3 KEY
7 KEY
8 KEY
DOWN
4 KEY
5 KEY
6 KEY
F/B KEY
0 KEY
CUT-OFF/
BKGD mode
LATERAL mode
R-DRIVE
B-DRIVE
CUT-OFF mode
50 Hz ADJUST mode COLOUR ADJUST mode
50 Hz ADJUST mode COLOUR ADJUST mode
Y-DY/OP ADJUST mode 60 Hz ADJUST mode SUB-ADJUST mode
In the direction of arrow : CH DOWN key
In the opposite direction : CH UP key
CUT-OFF/BKGD mode
3-sec time out3-sec time out
3-sec time out3-sec time out
9 KEY
In the direction of arrow : CH DOWN key
In the opposite direction : CH UP key
* The characters in parentheses appear on the on-screen display.
SECAM R-Y (R-Y)
SECAM B-Y (B-Y)
SUB CONTRAST (SUB CON)
SUB BRIGHT (SUB BRI)
SUB COLOUR (SUB COL)
SUB SUBTINT ( SUB TIN)
SUB SHARPNESS (SUB SHARP)
Y-SUB CONTRAST (Y SUB CON)
SUB-ADJUST mode
V-AMP 60 Hz (V-AMP60)
V-LINE 60 Hz (V-LINE60)
VS-CORRECT 60 Hz
V-PHASE 60 Hz (V-CENTER60)
H-PHASE 60 Hz (H-CENTER60)
V-BLK START 60 Hz (V-BLK ST60)
V-BLK STOP 60 Hz (V-BLK SP60)
60Hz ADJUST mode
Y DELAY PAL (DT PAL TV/AV)
Y DELAY SECAM (ST SECAM TV/AV)
Y DELAY NTSC (DT NTSC TV/AV)
Y DELAY B/W (DT BW TV/AV)
VIDEO MUTE ON/OFF (V-MUTE)
VIDEO 2 ON/OFF (AV2)
(DELAY A/V effective in A/V mode)
Y-DY/OPTION mode
In the direction of arrow : CH DOWN key
In the opposite direction : CH UP key
* The characters in parentheses
appear on the on-screen display.

5
5-1 5-2
20CT-250
INITIAL SETTINGS OF CHANNEL SELECTION DATA
(1) Make an entry of MCL1 in the service mode in order to set the following channel selection data to the
E2PROM. And select the POS1 channel. (An MCL2, -3 or -4 input makes different settings.)
*To go to the service mode, the data at the E2PROM’s addresses 00H thru 03H are read. If the data are not as
given below, the E2PROM is initialized according to the table below.
Address: Data
00H : 23H 02H : 13H
01H : 20H 03H : 61H
E2PROM item Data adjustable range Data initial value Remarks
(00H) –––––––––– 23H
(01H) –––––––––– 20H
(02H) –––––––––– 13H
(03H) –––––––––– 61H
R CUT OFF 0 ~255 0
G CUT OFF 0 ~255 0
B CUT OFF 0 ~255 0
G DRIVE 0 ~255 127
B DRIVE 0 ~255 127
50Hz V-AMP 0 ~127 58
50Hz V-LINEARITY 0 ~31 16
50Hz S-CORRECTION 0 ~127 67 *1
50Hz V-PHASE 0 ~75–3*1
50Hz H-PHASE 0 ~31 7 +5 *1
V-BLK ST 50 0 ~63 58→63 (50Hz)
V-BLK SP 50 0 ~127 25
60HzV-AMP 0 ~127 59
60HzV-LINEARITY 0 ~31 14
60Hz S-CORRECTION 0 ~127 74 *2
60Hz V-PHASE 0 ~72 *4
60Hz H-PHASE 0 ~31 12
60Hz V BLK ST 0 ~63 60→63 (60Hz)
60Hz V BLK SP 0 ~127 20
SECAM R-Y 0 ~15 10
SECAM B-Y 0 ~15 6
SUB-CONTRAST 0 ~255 255 *2
SUB-BRIGHT 0 ~255 127
SUB-COLOUR 0 ~255 110
SUB-TINT 0 ~127 70
SUB-SHARPNESS 0 ~63 28
Y SUB-CONTRAST 0 ~31 18 *2
DT PAL TV/AV 0 ~7 2/2 *2
DT SECAM TV/AV 0 ~7 4/4 *2
DT NTSC TV/AV 0 ~7 2/2 *2
DT B/W TV/AV 0 ~7 2/2 *2
V-MUTE ON/OFF OFF
A/V 2 1/2 1
NVM With all the adjustments complete, do not change the data of addresses 00H thru 03H. Other-
wise the E2PROM will be initialized when the AC power is turned on.
*1 : These data are additionally adjusted for 60Hz based on the 50Hz settings.
*2 : Unless otherwise specified, these data are fixed and need no adjustment.
*4 : Only 0 through 5 must be used in changing the data.
POS RECEPTION FREQ (MHZ) S-SYSTEM
1 48.25 B/G
2 62.25 B/G
3 77.25 D/K
4 175.25 B/G
5 182.25 B/G
6 183.25 D/K
7 191.25 D/K
8 196.25 D/K
9 210.25 B/G
10 224.25 B/G
11 471.25 B/G
12 487.25 I
13 503.25 B/G
14 575.25 B/G
15 599.25 B/G
16 621.25 –
17 639.25 D/K
18 703.25 B/G
19 735.25 I
20 767.25 B/G
POS RECEPTION FREQ (MHZ) S-SYSTEM
21 815.25 B/G
22 855.25 I
23 855.25 B/G
24 55.25 B/G
25 83.25 B/G
26 183.25 –
27 193.25 –
28 471.25 B/G
29 477.25 –
30 693.25 –
31 885.25 B/G
32 112.25 B/G
33 168.25 B/G
34 FREE –
35 294.25 B/G
36 463.25 B/G
37 FREE –
38 647.25 B/G
39 663.25 B/G
40 679.25 B/G
FACTORY SETTING
(1) The following key-in data have been factory-set for the E2PROM.
Item Setting
SKIP OFF
AFT ON
C-SYSTEM AUTO
S-SYSTEM B/G
LAST POWER ON
LAST TV/AV TV
DIGIT 1DIG
LANGUAGE THAI
BLUE BACK ON
LAST POS 1
LAST FB POS 1
VOLUME MIN
CONTRAST MAX
COLOUR CENT
BRIGHTNESS CENT
TINT CENT
SHARPNESS CENT

6
6-1 6-2
20CT-250
PIF/AFT/AGC ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
VCO adjust-
ment: T203 1. Disconnect the antenna from the tuner antenna terminal.
2. Apply DC voltage to pin (4) of IC201 (IF AGC).
»DC voltage: 6.0 V (allowable +0.1 V)
3. Using a digital voltmeter, measure the DC volt-
age at pin (20)(PLL FIL) of IC201.
* The digital voltmeter must be able to take read-
ings down to the third decimal place.
4. Relieve pin (4) of IC201 of the DC voltage.
5. Reconnect the antenna in position and receive
the E-12CH signal. (With the AFT off, adjust the
receiving frequency to 224.25 MHz.)
6. Connect the DC digital voltmeter to pin (20) of
IC201. Adjust T203 so that the voltmeter should
read the same voltage as in Step 3.
Allowable error : 0.015 V (20 kHz)
1* Warm upthe unitfor longerthan
10 minutes in advance.
* 10 kHz at about 0.007 V.
* Position the T203 core in the
range in which the Colour Bar
signal can be received.
AFT
adjustment:
T204
1. Receive the PAL Colour Bar signal. If this signal
isnot available, any signalabove the E-5CHband
is acceptable.
»Field strength : 55-80 dBµV
Make sure the frequency is almost the same as
that of the received channel (±30 kHz).
2. Using the channel setting control, make a fre-
quency of 224.25 MHz appear on the screen (the
AFT turns off). If any other channel than Colour
Barisreceived, make itsfrequency on thescreen.
(The AFT turns off when the on-screen display
turns yellow.)
3. Turn T204 clockwise to have a 6V point, and
counterclockwise to have a 0.2V point. Position
the coil at the center of these two points.
4. Adjust T204 so that the DC voltage at pin (1) (AFT
OUT terminal) of IC201 be 3.3 ±0.1 V. (See Fig. 3 )
2
RF AGC
cut-in
adjustment:
R216
1. Receive the PAL Colour Bar signal.
»Field strength : 57 ±1 dBµV (75 ohms open)
2. Connect the oscilloscope to TP210, as shown in
Fig. 4 .
3. Turn R216 to have the highest voltage.
4. Turn R216 slowly in the opposite direction until the
voltage goes down 0.1 V below the highest level.
5. Adjust the signal level to 63-67 dBµV and make
sure there is no noise.
6. Nowadjustthe signallevelto90-95 dBµVandmake
sure there is no chrominance modulation beat.
3
6V
3.3V
DOWN A B' B B" C UP
DC voltage at TP201
Fig. 3
»Bias box: About 4.5 V
Oscilloscope
0.1V
TV Set
Bias box
TP210+
+
–
–
Fig. 4
PIF CHECKING
No. Adjusting point Adjusting procedure/conditions Waveform and others
Tuner IFT
(preset):
TU201
1. Get the tuner ready to receive the E-9CH signal.
but with no signal input. Adjust the PLL data.
2. Connect the sweep generator’s output cable to
the tuner antenna. (RF sweep)
3. Adjust the sweep generator’s output level to 80
dBµV.
4. Connectthe response lead(use a low-impedance
probe with wave detector; see
Fig. 1 ) to the tun-
er’s IF output terminal.
(This terminal must have the probe alone con-
nected.)
5. Set the RF AGC voltage to 0-6 V with no contact
with the waveform.
6. Adjust the tuner IF coil to obtain the waveform as
shown in Fig. 2 .
Note: Be sure to keep the tuner cover in posi-
tion during this adjustment.
1
IF-OUT
1000p 10kΩ
75Ω1000p 100kΩ
Oscilloscope
Fig. 1
E-9CH
PC
– 1.5dB ±0.8dB
Fig. 2
SERVICE ADJUSTMENT
115V ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
115V
adjustment:
R711
1. Receive the Monoscope Pattern signal.
2. Set to the P-NORM mode.
3. Connect a DC milliammeter between TP602(–)
and TP603(+).
4. Take the beam ammeter reading to make sure
that the beam current is between 900 µA and
1100 µA.
* If not, readjust the FBT screen control to ob-
tain the beam current of 900-1100 µA.
5. Connect a digital voltmeter to TP701.
6. Adjust R711 so that the digital voltmeter should
read 115 ±0.5 V.
1

7
7-1 7-2
20CT-250
CONVERGENCE ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
Convergence
adjustment
(to be done
after the purity
adjustment)
1. Receive the Crosshatch Pattern signal.
2. Usingthe remote controller,call the Normalmode.
STATIC CONVERGENCE
1. Turn the 4-pole magnet to a proper opening an-
gle in order to superimpose the blue and red col-
ours.
2. Turn the 6-pole magnet to a proper opening an-
glein order tosuperimpose thegreen colourover
the blue and red colours.
DYNAMIC CONVERGENCE
1. Adjust the convergence on the fringes of the
screen in the following steps.
a)
Fig. 6-1 : Drive the wedge at point “a” and
swing the deflection coil upward.
b) Fig. 6-2 : Drive the wedges at points “b” and
“c”and swing the deflection coildownward.
c) Fig. 6-3 : Drive the “c” wedge deeper and
swing the deflection coil rightward.
d) Fig. 6-4 : Drive the “b” wedge deeper and
swing the deflection coil leftward.
2. Fix all the wedges on the cathode ray tube and
apply glass tape over them.
3. Apply lacquer to the deflection yoke lock screw,
magnet unit (purity, 4-pole and 6-pole magnets),
and magnet unit lock screw.
Finally receive the red-only and blue-only signals
and make sure there is no other colour mixed on
the screen.
1
RGB
BGR
R
G
B
R
G
B
B
G
R
B
G
R
RGB
BGR
Fig. 6-2
Fig. 6-1
Fig. 6-3
Fig. 6-4
Fig. 6-5
Fig. 6-6
Lacquer
Wedge "a"
Wedge
"b" Wedge
"c"
About
100°
About
100°
4-pole magnet
6-pole magnet
CRT neck
Lacquer
Purity magnet
PURITY ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
Purity
adjustment 1. Using the remote controller, make the screen colour green-only.Adjustthecontrastcontroltohaveabeam
current of about 700 µA.
2. Degauss the cathode ray tube enough with the
degaussing coil.
3. Keep the purity magnet in the zero magnetic field
in advance. Roughly adjust the convergence.
4. Observe the points “a” and “b”, as shown in
Fig.
5-1 , through a microscope. Adjust the landing to
the rank “A” requirements.
5. Adjust the raster rotation to “0” eastward.
6. Tighten up the deflection coil screws.
»Tightening torque: 108 ±20 N (11 ±2 kgf)
7. While observing the cathode ray tube corners.
apply the magnet sheet to have the landing at
rank “A”.
Note:Before starting this adjustment, warm
up the unit for 30 minutes or longer at
a beam current of over 700 µA.
Note: Set the service switch S1001 to call the
service mode and press the single-col-
our key on the process remote control-
ler to get the green-only screen.
* Each time the single-colour key is pressed, the
screen colour changes as follows.
1
* Whether in the service mode or
not, hold down the single-colour
key for 1 second or longer and
the service mode is called.
TheTEXTkey or the R.G.Cykey
may be used instead to provide
the single-colour screens.
ab
A
B
A
B
A = B
A = B
Rank "A" (on the
right of the CRT)
Rank "A" (on the
left of the CRT)
Fig. 5-1
Fig. 5-2
Fig. 5-3
Green-only
screen Blue-only
screen Red-only
screen
Single-colour
screen cleared

8
8-1 8-2
20CT-250
No. Adjusting point Adjusting procedure/conditions Waveform and others
Maximum
beam current
(check item)
1. Receive the Monoscope Pattern signal.
2. Set to the P-NORM mode.
3. Connect the DC ammeter between TP602 and
TP603.
»Ammeter’s full-scale : 3 mA range
»Ammeter’s positive (+) lead : TP603
»Ammeter’s negative (-) lead : TP602
4. Make sure the beam current is 1,100 ±100 µA.
Note:Before starting this adjustment, warm
up the unit for 30 minutes or longer at
a beam current of over 700 µA.
3
HORIZONTAL AND VERTICAL CIRCUIT ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
V-AMP 50
V-LINEARITY -
50 Hz
V-S CORREC-
TION - 50 Hz
V-SHIFT 50 (V-
CENTER)
H-SHIFT (50)
(H-CENTER)
1. Adjust the overscan to 9% typical.
1. Adjust to get the best linearity.
1. Adjust the proper condition.
1. Align the screen center with the CRT's geometri-
cal center (E-5).
1. Align the screen center with the CRT's geometri-
cal center (E-5).
Note: For the V-AMP 60, V-LINEARITY 60, V-S
CORRECTION 60, V-SHIFT 60 and H-
SHIFT 60 adjustments, their corrected
data are automatically entered when the
corresponding 50 Hz mode adjustments
are made.
1The selected channels in paren-
theses have the following signals.
(E-2): crosshatch pattern (50 Hz)
signal
(E-5): monoscopepattern (50 Hz)
signal
Focus adjust-
ment 1. Receive the Monoscope Pattern signal. 2. Set to the P-NORM mode.
3. Adjust the focus control so that the screen be in
best focusing.
2
CRT CUT-OFF, SUB-CONTRAST, WHITE BALANCE AND SUB
BRIGHTNES ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
CRT cut-off
adjustment:
I2C bus control
adjustment
1. Receive the Monoscope Pattern signal.
2. Set to the P-NORM mode.
3. Turn on the service switch and select the "Cut-
off/background" mode.
4. Set the screen control to 0/10 position.
5. Pressthe “9” keyon the remote controllerto reach
the horizontal centering mode.
6. Turn the screen control clockwise until the hori-
zontal raster of the first glimmering colour be-
comes slightly visible.
7. Adjust the cut-off data of the other two colours
until the horizontal raster becomes whitish.
8. Turnoffthescreen control (counterclockwise) until
the horizontal raster disappears.
Note:Before starting this adjustment, warm
up the unit for 30 minutes or longer at
a beam current of over 700 µA.
9. Press the “9” key on the remote controller to call
the NORMAL mode.
1* First of all, make sure that the
R/G/B cut-off data are all initial
values.
Note:
R CUT OFF UP “1” KEY
DOWN “4” KEY
G CUT OFF UP “2” KEY
DOWN “5” KEY
B CUT OFF UP “3” KEY
DOWN “6” KEY
The data can be turned up and
down with the above keys.
1. Receive the Monoscope Pattern signal.
2. Set to the P-NORM mode.
3. Connect the DC miliammeter between TP602 (-)
and TP603 (+).
» Full Scale: 3.0mA range
4. Make sure the beam current be 1,100µA.
5. Adjust the "G-DRIVE" and "B-DRIVE" data to have
a colour temperature of 12,300°K (white).
6. Adjust the contrast and brightness control to have
a beam current of 200µA.
Ifthecolour temperature is notat12,300°K, go back
to step1 above.
7. Receive the Crosshatch Pattern signal.
8. Adjust the "SUB BRI" bus data, so that the block
1st to 3rd inside the window area will
disappear.(black)
2Sub contrast,
white balance,
& sub bright-
ness Service
mode adjust-
ment:
I2C Bus Con-
trol Adjust-
ment
* 12,300°K X: 0.273
Y: 0.276
(with colour temperature meter
CA-100(MINOLTA).)
Note:
G-DRIVE UP “7” KEY
DOWN “-/--” KEY
B-DRIVE UP “8” KEY
DOWN “0” KEY
The data can be turned up and
down with the above keys.
1 2 3 4 5
Make sure all the 1st, 2nd
and3rd blackportions are at
the same black level.

9
9-1 9-2
20CT-250
PROTECTOR PERFORMANCE CHECK
No. Adjusting point Adjusting procedure/conditions Waveform and others
Beam protector 1. Receive the Monoscope Pattern signal.
2. Set the contrast control to maximum.
3. Set the brightness control to maximum.
4. Make a short-circuit between the collector and
emitter of Q851, Q852 or Q853 and make sure
that the protector is activated and the stand-by
mode is called.
1
High-voltage
protector 1. Receive the Monoscope Pattern signal. 2. Connect the bias box to the cathode (R635 side)
of D607.
3. Adjustthe bias boxvoltage to 18V and make sure
that the protector is not activated.
4. Adjustthe bias boxvoltage to 27V and make sure
that the protector is not activated.
2
Other protec-
tors 1. In checking the performance of other protectors — for example, the one against shorting of
smoothing electrolyticcapacitor of +B line—, pay
attentionnot to damageor deteriorate anyrelated
element.
3
A/V INPUT AND OUTPUT CHECK
No. Adjusting point Adjusting procedure/conditions Waveform and others
Video and
audio output
check
1. Receive the Colour Bar (100% white colour bar,
400 Hz, 100% modulation audio) signal.
2. Terminate the video output with a 75 ohm imped-
ance. Make sure the output is as specified
(1.0 Vp-p ±3 dB).
3. Terminate the audio output with a 10k ohm im-
pedance. Make sure the output is as specified
(1.76 Vp-p ±3 dB).
1
Video and
audio input
check
1. Using the TV/AV key on the remote controller,
make sure that the modes change in the order of
TV, AV and TV again and that the video and au-
dio outputs are according to the input and output
terminals for each mode.
2
PAL CHROMA ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
Sub-colour
adjustment:
I2C bus
adjustment
1. Receive the PAL Colour Bar signal.
2. Set to the P-NORM mode.
3. Connect the oscilloscope to TP852 (RED cath-
ode). (Use a 10 : 1 probe.)
»Range : 2 V/div.
»Sweep time : 20 µsec/div.
4. Using the remote controller, call the sub-colour
adjustment mode. Adjust the sub-colour data so
that the 75% white and red portions of the PAL
colour bar be at the same level. See Fig. 7 .
5. Clear the adjustment mode.
1
NTSC CHROMA ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions Waveform and others
Sub-tint
adjustment:
I2C bus
adjustment
1. Receive the NTSC 3.58 Colour Bar signal in the
A/V mode.
2. Connect the oscilloscope to pin (36) of IC801(B-
Y) .
»Range : 20 mV/div.
»Sweep time : 20 µsec/div.(Use a 10 : 1 probe.)
3. Adjust the sub-tint data to obtain the waveform
as shown in Fig. 8 .
4. Clear the adjustment mode.
1
Cy GB
WY 100%W
Fig. 7
Mg R
WYCy G Mg R B
Fig. 8
A=B=C
(B–Y)
A
B
C

10
10-1 10-2
20CT-250
No. Adjusting point Adjusting procedure/conditions Waveform and others
FUNCTION CHECK (VIDEO AND AUDIO)
No. Adjusting point Adjusting procedure/conditions Waveform and others
Contrast key 1. Receive the E-5CH signal.
2. Select the contrast on the P-MODE screen.
3. Check whether the Contrast is OK or not with Up/
Down keys.
1
COLOUR
SYSTEM key 1. Receive the NTSC 3.58 colour bar (A/V) signal. Using the COLOUR SYSTEM key, select a mode
other than N3.58 and make sure the colour sys-
tem does not work properly.
8
Channel sign
display colour 1. The display colour of all the channel (0-99) signs must be green Under the AFT on mode.
7
Noise mute
check 1. Receive the PAL Colour Bar signal. 2. Turn upthe sound volume to maximumand make
sure the sound is heard normally from the speak-
ers. Then cut off the signal.
3. Make sure the sound muting functions.
4. Finally turn down the sound volume to minimum.
10
Bilingual Key 1. Receive Bilingual sound signal, press the "Bilin-
gual" key. Check whether there is change
SOUND-1 to SOUND-2.
9
Sharpness key 1. Receive the E-5CH signal.
2. Select the sharpness on the P-MODE screen.
3. Check whether the Sharpness is OK or not with
Up/Down keys.
6
PIC-Normal.
key 1. Press the Normal key on the P-MODE screen to make sure all the displayed items are at normal
settings.
See below for the normal settings.
»Contrast : MAX
»Colour : CENTER
»Brightness : CENTER
»Tint : CENTER
»Sharpness : CENTER
5* Thecontrast, colour,brightness,
tint and sharpness settings are
all normal when these items do
not appear on the screen.
Colour key 1. Receive the E-12CH signal.
2. Select the colour on the P-MODE screen.
3. Check whether the Colour is OK or not with Up/
Down keys.
2
Brightness
key 1. Receive the E-5CH signal. 2. Select the brightness on the P-MODE screen.
3. Check whether the Brightness is OK or not with
Up/Down keys.
3
Tint key 1. Receive theNTSC colour barsignal. (A/V In Only)
2. Select the tint on the P-MODE screen.
3. The tint must be changeable toward green with
the UP key and toward red with the DOWN key.
4