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COLOUR TV SET
Models:
14CT01
21CT21FS
21CT24FS
21CT71FS
SERVICE MANUAL
www.akai.ru
SERVICE MANUAL
TABLE OF CONTENTS
TABLE OF CONTENTS............................................................................................... 1
SAFETY INSTRUCTIONS AND MAINTENANCE ................................... 2
X-RAY RADIATION PRECAUTION ........................................................................................ 2
SAFETY PRECAUTIO .......................................................................................................
N 2
PRODUCT SAFETY NOTICE................................................................................................ 3
SAFETY SYMBOL DESCRIPTION ........................................................................................ 3
MAINTENANCE ................................................................................................................... 4
ADJUSTMENTS ......................................................................................................... 4
SET-UP ADJUSTMENTS...................................................................................................... 4
CIRCUIT ADJUSTMENTS .................................................................................................... 7
CONTROL BUTTONS ........................................................................................... 13
CONTROL BUTTONS ........................................................................................................ 13
REMOTE CONTROL .......................................................................................................... 14
STRUCTURE AND CHASSIS FUNCTION DESCRIPTION .............. 21
STRUCTURE BLOCK DIAGRAM ......................................................................................... 21
BLOCK DIAGRAM FOR SUPPL Y VOLTAGE SYSTE ..........................................................
M 22
CHASSIS DESCRIPTION ................................................................................................... 23
SERVICE DATA ........................................................................................................ 24
TECHNICAL DATA OF KEY ICS .......................................................................................... 24
WAVEFORMS OF KEY POINTS .......................................................................................... 42
SERVICE DA TA OF KEY ICS .............................................................................................. 43
REPLACEMENT OF PARTS ............................................................................................... 47
APPENDIX
1. CIRCUIT DIAGRAMS
2
INSTRUCTIONS FOR SERVICE SAFETY AND MAINTENANCE
WARNING: BEFORE SERVICING THIS CHASSIS, READ THE "X-RAY RADIATION PRECAUTION",
"SAFETY PRECAUTION" AND "PRODUCT SAFETY NOTICE" INSTRUCTION BELOW.
X-RAY RADIATION PRECAUTION
1. The EHT must be checked every time the TV is serviced to ensure that the CRT does not emit
X-ray radiation as result of excessive EHT voltage. The maximum EHT voltage permissible in any
operating circumstances must not exceed the rated value. When checking the EHT, use the High
Voltage Check procedure in this manual using an accurate EHT voltmeter.
2. The only source of X-RAY radiation in this TV is the CRT. The TV minimizes X-RAY radiation, which
ensures safety during normal operation. To prevent X-ray radiation, the replacement CRT must be
identical to the original fitted as specified in the parts list.
3. Some components used in this TV have safety related characteristics preventing the CRT from
emitting X-ray radiation. For continued safety, replacement component should be made after
referring the PRODUCT SAFETY NOTICE below.
4. Service and adjustment of the TV may result in changes in the nominal EHT voltage of the CRT
anode. So ensure that the maximum EHT voltage does not exceed the rated value after service
and adjustment.
SAFETY PRECAUTION
WARNING: REFER SERVICING TO QUALIFIED SERVICE PERSONNEL ONLY
1. The TV has a nominal working EHT voltage of 25kV. Extreme caution should be exercised when
working on the TV with the back removed.
1.1 Do not attempt to service this TV if you are not conversant with the precautions and procedures for
working on high voltage equipment.
1.2 When handling or working on the CRT, always discharge the anode to the TV chassis before
removing the anode cap in case of electric shock.
1.3 The CRT, if broken, will violently expel glass fragments. Use shatterproof goggles and take extreme
care while handling.
1.4 Do not hold the CRT by the neck as this is a very dangerous practice.
2. It is essential that to maintain the safety of the customer all power cord forms be replaced exactly
as supplied from factory.
3. Voltage exists between the hot and cold ground when the TV is in operation. Install a suitable
isolating transformer of beyond rated overall power when servicing or connecting any test
equipment for the sake of safety.
4. When replacing ICs, use specific tools or a static-proof electric iron with small power (below 35W).
5. Do not use a magnetized screwdriver when tightening or loosing the deflection yoke assembly to
2
avoid electronic gun magnetized and decrement in convergence of the CRT.
6. When remounting the TV chassis, ensure that all guard devices, such as nonmetal control buttons,
switch, insulating sleeve, shielding cover, isolating resistors and capacitors, are installed on the
original place.
7. Replace blown fuses within the TV with the fuse specified in the parts list.
8. When replacing wires or components to terminals or tags, wind the leads around the terminal
before soldering. When replacing safety components identified by the international hazard symbols
on the circuit diagram and parts list, it must be the company-approved type and must be mounted
as the original.
9. Keep wires away from high temperature components.
PRODUCT SAFETY NOTICE
CAUTION: FOR YOU PROTECTION, THE FOLLOWING PRODUCT SAFETY NOTICE SHOULD BE
READ CAREFULLY BEFORE OPERATING AND SERVICING THIS TV SET
1. Many electrical and mechanical components in this chassis have special safety-related
characteristics. These characteristics are often passed unnoticed by a visual inspection and the
X-ray radiation protection afforded by them cannot necessarily be obtained by using replacements
rated at higher voltages or wattage, etc. Components which have these special safety
characteristics in this manual and its supplements are identified by the international hazard
symbols on the circuit diagram and parts list. Before replacing any of these components read the
parts list in this manual carefully. Substitute replacement components which do not have the same
safety characteristics as specified in the parts list may create X-ray radiation.
2. Do not slap or beat the cabinet or CRT, since this may result in fire or explosion.
3. Never allow the TV sharing a plug or socket with other large-power equipment. Doing so may result
in too large load, causing fire.
4. Do not allow anything to rest on or roll over the power cord. Protect the power cord from being
walked on, modified, cut or pinched, particularly at plugs.
5. Do not place any objects, especially heavy objects and lightings, on top of the TV set. Do not install
the TV near any heat sources such as radiators, heat registers, stove, or other apparatus that
produce heat.
6. Service personnel should observe the SAFETY INSTRUCTIONS in this manual during use and
servicing of this TV set. Otherwise, the resulted damage is not protected by the manufacturer.
SAFETY SYMBOL DESCRIPTION
The lightning symbol in the triangle tells you that the voltage inside this product may be
strong enough to cause an electric shock. Extreme caution should be exercised when
working on the TV with the back removed.
3
This is an international hazard symbol, telling you that the components identified by the
symbol have special safety-related characteristics.
FDA This symbol tells you that the critical components identified by the FDA marking have
special safety-related characteristics.
UL This symbol tells you that the critical components identified by the UL marking have
special safety-related characteristics.
C UL This symbol tells you that the critical components identified by the C-UL marking have
been evaluated to the UL and C-UL standards and have special safety-related
characteristics.
VDE This symbol tells you that the critical components identified by the VDE marking have
special safety-related characteristics.
MAINTENANCE
1. Install the TV set on a stable and level surface. Do not place the set near or over a radiator or heat
register, or where it is exposed to direct sunlight.
2. Do not install the TV set in a place exposed to rain, water, excessive dust, mechanical vibrations or
impacts.
3. Allow enough space (at least 10cm) between the TV and wall or enclosures for proper ventilation.
4. Slots and openings in the cabinet should never be blocked by clothes or other objects.
5. Please power off the TV set and disconnect it from the wall immediately if any abnormal condition
are met, such as bad smell, belching smoke, sparkling, abnormal sound, no picture/sound/raster.
Hold the plug firmly when disconnecting the power cord.
6. Unplug the TV set from the wall outlet before cleaning or polishing it. Use a dry soft cloth for
cleaning the exterior of the TV set or CRT screen. Do not use liquid cleaners or aerosol cleaners.
ADJUSTMENTS
SET-UP ADJUSTMENTS
The following adjustments should be made when a complete realignment is required or a new picture
tube is installed.
Perform the adjustments in the following order:
1. Color purity
2. Convergence
3. White balance
Notes:
The purity/convergence magnet assembly and rubber wedges need mechanical positioning.
4
For some picture tubes, purity/ convergence adjustments are not required.
1. Color Purity Adjustment
Preparation:
Before starting this adjustment, adjust the vertical sync, horizontal sync, vertical amplitude and
focus.
1.1 Face the TV set north or south.
1.2 Connect the power plug into the wall outlet and turn on the main power switch of the TV set.
1.3 Operate the TV for at least 15 minutes.
1.4 Degauss the TV set using a specific degaussing coil.
1.5 Set the brightness and contrast to maximum.
1.6 Counter clockwise rotate the R /B low brightness potentiometers to the end and rotate the green
low brightness potentiometer to center.
1.7 Receive green raster pattern signals.
1.8 Loosen the clamp screw holding the deflection yoke assembly and slide it forward or backward to
display a vertical green zone on the screen. Rotate and spread the tabs of the purity magnet
around the neck of the CRT until the green zone is located vertically at the center of the screen.
1.9 Slowly move the deflection yoke assembly forward or backward until a uniform green screen is
obtained.
1.10 Tighten the clamp screw of the assembly temporarily. Check purity of the red raster and blue raster
until purities of the three rasters meet the requirement.
Dummy Wedge
Deflection Coil
Rubber Wedge
Adhesive
Purity/Convergence
Magnet Module Deflection Yoke
Glass Cloth Tapes
Fig.1
5
6-pole Magnet
Fixed
4-pole Magnet
Adjust the Angle (Vertical Lines)
Rotate Two Tabs At the
Same Time (Horizontal Lines)
Purity Magnet Adjustment of Magnets
Convergence Magnet Assembly
Fig.2
2. Convergence Adjustment
Preparation:
Before attempting any convergence adjustment, the TV should be operated for at least 15 minutes.
2.1 Center convergence adjustment
2.1.1 Receive dot pattern.
2.1.2 Adjust the brightness/contrast controls to obtain a sharp picture.
2.1.3 Adjust two tabs of the 4-pole magnet to change the angle between them and red and blue
vertical lines are superimposed each other on the center of the screen.
2.1.4 Turn both tabs at the same time keeping the angle constant to superimpose red and blue
horizontal on the center of the screen.
2.1.5 Adjust two tabs of the 6-pole magnet to superimpose red/blue line and green line.
2.1.6 Remember red and blue movement. Repeat steps 3) 5) until optimal convergence is
obtained.
2.2 Circumference convergence adjustment
2.2.1 Loosen the clamp screw holding the deflection yoke assembly and allow it tilting.
2.2.2 Temporarily put the first wedge between the picture tube and deflection yoke assembly. Move
front of the deflection yoke up or down to obtain better convergence in circumference. Push the
mounted wedge in to fix the yoke temporarily.
2.2.3 Put the second wedge into bottom.
2.2.4 Move front of the deflection yoke to the left or right to obtain better convergence in
circumference.
2.2.5 Fix the deflection yoke position and put the third wedge in either upper space. Fasten the
deflection yoke assembly on the picture tube.
6
2.2.6 Detach the temporarily mounted wedge and put it in either upper space. Fasten the deflection
yoke assembly on the picture tube.
2.2.7 After fastening the three wedges, recheck overall convergence and ensure to get optimal
convergence. Tighten the lamp screw holding the deflection yoke assembly.
BLU Red Red/BLU GRN
BLU Red/BLU
Red GRN
4-pole Magnet Movement 6-pole Magnet Movement
Center Convergence by Convergence Magnets
Incline the Yoke up (or down) Incline the Yoke Right(or left)
Circumference Convergence by DEF Yoke
Fig. 3
3. White Balance Adjustment
Generally, white balance adjustment is made with professional equipment. It's not practical to get
good white balance only through manual adjustment. For TVs with I2C bus control, change the bus
data to adjust white balance.
CIRCUIT ADJUSTMENTS
Preparation:
Circuit adjustments should be made only after completion of set-up adjustments.
Circuit adjustments can be performed using the adjustable components inside the TV set. For TVs with
I2C bus control, first change the bus data.
1. Degaussing
A degaussing coil is built inside he TV set. Each time the TV is powered on, the degaussing coil will
automatically degauss the TV. If the TV is magnetized by external strong magnetic field, causing
color spot on the screen, use a specific degausser to demagnetize the TV in the following ways.
Otherwise, color distortion will be shown on the screen.
7
1.1 Power on the TV set and operate it for at least 15 minutes.
1.2 Receive red full-field pattern.
1.3 Power on the specific degausser and face it to the TV screen.
1.4 Turn on the degausser. Slowly move it around the screen and slowly take it away from the TV.
1.5 Repeat the above steps until the TV is degaussed completely.
2. Supply Voltage Adjustment
Caution: +B voltage has close relation to high voltage. To prevent X-ray radiation, set +B voltage to
the rated voltage.
2.1 Make sure that the supply voltage is within the range of the rated value.
2.2 Connect a digital voltmeter to the +B voltage output terminal of the TV set. Power on the TV and set
the brightness and sub-brightness to minimum.
2.3 Regulate voltage adjustment components on the power PCB to make the voltmeter read 115