Changhong ETA-1D Schematic
COLOR TELEVISION
SERVICE MANUAL
MODEL NO.
PF29GA18A
CHASSIS NO. ETA-1D
Please read this manual carefully before service.
TABLE OF CONTENTS
SAFETY INSTRUCTIONS AND MAINTENANCE .......................................1
X-RAY RADIATION PRECAUTION.............................................................................…..........1
SAFETY PRECAUTION ...............................................................................................….........1
PRODUCT SAFETY NOTICE......................................................................................…..........2
SAFETY SYMBOL DESCRIPTION .............................................................................…..........3
MAINTENANCE............................................................................................................….........3
ADJUSTMENTS .......................................................................................................….......4
SET-UP ADJUSTMENTS .............................................................................................….........4
CIRCUIT ADJUSTMENTS............................................................................................….........7
STRUCTURE AND CHASSIS FUNCTION DESCRIPTION.............…..13
STRUCTURE BLOCK DIAGRAM ..................................................................................…......13
CHASSIS DESCRIPTION..........................................................................................……......14
SERVICE DATA.................................................................................................….....…....15
TECHNICAL DATA OF KEY ICS ............................................................................…....….....15
SERVICE DATA OF KEY ICS.................................................................................…....….....38
APPENDIX
CIRCUIT DIAGRAM
SERVICE MANUAL
SAFETY INSTRUCTIONS 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
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.
identical to the original fitted as specified in the parts list.
SAFETY PRECAUTION
WARNING: REFER SERVICING TO QUALIFIED SERVICE PERSONNEL ONLY.
1. The TV has a nominal working EHT voltage. 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.
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SERVICE MANUAL
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
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 YOUR 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.
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SERVICE MANUAL
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.
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
VDE
characteristics.
This symbol tells you that the critical components identified by the VDE marking have
special safety-related characteristics.
MAINTENANCE
1. Place the TV set on a stable stand or base that is of adequate size and strength to prevent it from
being accidentally tipped over, pushed off, or pulled off. 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.
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SERVICE MANUAL
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:
① The purity/convergence magnet assembly and rubber wedges need mechanical positioning.
② 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.
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SERVICE MANUAL
Yok
Fig. 1
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 2.1.3～2.1.5 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
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SERVICE MANUAL
deflection yoke assembly on the picture tube.
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.
Fig. 2
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
3. White Balance Adjustment
Fig.3
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 I
data to adjust white balance.
2
C bus control, change the bus
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SERVICE MANUAL
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
2
C bus control, first change the bus data.
I
1. Degaussing
A degaussing coil is built inside the 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.
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. Confirmation and Adjustment for Voltage
Caution: +B voltage has close relation to high voltage. To prevent X-ray radiation, set +B voltage to
the rated value.
2.1 Make sure that the supply voltage is within the range of the rated value.
2.2 Connect a digital voltmeter to the voltage output terminal of the main PCB. Power on the TV and set
the brightness and sub-brightness to minimum. Ensure that the voltage from the main PCB reads as
follows.
2.3 Regulate voltage adjustment components on the power section until the +B the voltage reaches the
rated value.
Table 1
Test Point Voltage (V) Test Point Voltage (V)
TP-130V (C821)
TP-17V (C822)
TP-5V-1 (C828)
TP-11V (C823)
TP-200V (C463)
135V±1.5V
15V±1V
5V±0.3V
10.5V±０．５V
195V±5V
TP-18V (C824)
TP-5V-2 (C827)
TP-8V (C826)
TP-26V (C461)
16V±1V
5V±0.3V
8V±0.5V
30V±3V
Note:
It’s impossible to check the power part separately from the main chassis board as the part is
mounted on the main chassis board. The power components, etc. should be checked for
burnout when power-on. If burned out, do not power on the TV again until the cause is found
.
out
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3. High Voltage Inspection
Measure voltages of test points on the main PCB with the digital voltmeter. Measure the CRT
high voltage with the high-voltage testing equipment and heater voltage with the high-frequency
effective voltmeter. The rated values are shown as below.
Table 2
Test Point Voltage (V)
Negative of VD461 29±3V
Negative of VD485 195±5V
CRT anode 29.5±1.5KV
Heater 6.3±0.3Vrms
4. Focus Adjustment
Caution: Dangerously high voltages are present inside the TV. Extreme caution should be
exercised when working on the TV with the back removed.
4.1 After removing the back cover, look for the FBT on the main PCB. There should be a FCB on
the FBT.
4.2 Power on the TV and preheat it for 15 min.
4.3 Receive a normal TV signal. Rotate knob of the FCB until you get a sharp picture.
Before Adjusting After Adjusting
Fig. 4
5. Safety Inspection
5.1 Inspection for insulation and voltage-resistant
Perform safety test for all naked metal of the TV. Supply high voltage of 3000V AC, 50Hz (limit
current of 10mA) between all naked metal and cold ground. Test every point for 3 sec. and
ensure no arcing and sparking.
5.2 Requirements for insulation resistance
Measure resistance between naked metal of the TV and feed end of the power cord to be
infinity with a DC-500 high resistance meter and insulation resistance between the naked metal and
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