Sunday, December 13, 2015

AKAI 25CT23FSR - 29CT23FSR How to enter to service mode adjustments and power supply circuit


Color Purity Adjustment
Before starting this adjustment, adjust the vertical sync, horizontal sync, vertical amplitude and focus.
1. Face the TV set north or south.
2. Connect the power plug into the wall outlet and turn on the main power switch of the TV set.
3. Operate the TV for at least 15 minutes.
4. Degauss the TV set using a specific degaussing coil.
5. Set the brightness and contrast to maximum.
6. Counter clockwise rotate the R /B low brightness potentiometers to the end and rotate the green low brightness potentiometer to center.
7. Receive green raster pattern signals.
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.
9. Slowly move the deflection yoke assembly forward or backward until a uniform green screen is obtained.
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.
Convergence Adjustment
Before attempting any convergence adjustment, the TV should be operated for at least 15minutes.
1.Center convergence adjustment
1. Receive dot pattern.
2. Adjust the brightness/contrast controls to obtain a sharp picture.
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.
4. Turn both tabs at the same time keeping the angle constant to superimpose red and blue horizontal on the center of the screen.
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. Circumference convergence adjustment
1. Loosen the clamp screw holding the deflection yoke assembly and allow it tilting.
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.
3. Put the second wedge into bottom.
4. Move front of the deflection yoke to the left or right to obtain better convergence in circumference.
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. Detach the temporarily mounted wedge and put it in either upper space. Fasten the
deflection yoke assembly on the picture tube.
7. After fastening the three wedges, recheck overall convergence and ensure to get optimal convergence. Tighten the lamp screw holding the deflection yoke assembly.
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 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 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 Power on the TV and receive Philips test pattern.
2.2 Check the resistors and coils for being burned. (If the fuse is burned out, do not power on the TV again until the cause is found out.)
2.3 Measure voltages of test points with the digital voltmeter. Measure the CRT high voltage with the high-voltage testing equipment and heater voltage with the high-frequency effective voltmeter.
Test Point
Voltage (V)
Negative of VD831
145 1.5V
Negative of VD461B
12 1V
Negative of VD832
15 1V
Positive of C462
17 1V
Positive of C452
47 3V
Positive of C492
195 5V
6.3 0.3Vrms
28.8KV 1KV
 3. High Voltage Inspection
Caution: No high voltage adjustment components inside the chassis. Please perform high voltage inspection in the following ways.
3.1 Connect a precise static high voltmeter to the second anode (inside the high voltage cap) of the CRT.
3.2 Plug in the supply socket (150-250V ~, 50Hz) and turn on the TV. Set the brightness and contrast to minimum (0u A).
3.3 The high voltage reading should be less than the limited EHT voltage.
3.4 Change the brightness from minimum to maximum, and ensure high voltage not beyond the limitation in any case.
Nominal EHT voltage: 28.8KV 1KV Limited EHT voltage: 32KV
Safety Inspection
1. Inspection for insulation and voltage-resistant
Perform safety test for all naked metal of the TV. Supply high voltage of 3000V, 50Hz (limit current of 10mA) between all naked metal and cold ground. Test every point for 3 sec. and ensure no arcing and sparking.
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 degaussing coil to be over 20M .
To enter the SERVICE mode
Set the volume to 0 by the remote control. Then press and hold the MUTE button on the remote control and MENU button on the TV at the same time for over 2 seconds. In the S mode, press the POWER button to quit the S mode.