Sunday, December 13, 2015

Akai PF21GB300 service mode and adjustments


To enter the DESIGN/SERVICE mode
Set the volume to 0. Then press and hold the MUTE button on the remote control, and press the MENU button on the TV to enter the SERVICE mode. To exit from the S mode, turn off the TV set by the POWER button on the remote control.
Caution: The user service mode adjustment can be changed only when service personnel adjust the whole set data during servicing. As the control data have dramatic effects on functions and performance of the TV, service personnel should not tell user how to enter the SERVICE mode to avoid improper data settings.
Safety Inspection
Inspection for insulation and voltage-resistant
Perform safety test for all naked metal of the TV. Supply high voltage of 2500V 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.
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 .
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.
Power on the TV set and operate it for at least 15 minutes.
Receive red full-field pattern.
Power on the specific degausser and face it to the TV screen.
Turn on the degausser. Slowly move it around the screen and slowly take it away from the TV.
Repeat the above steps until the TV is degaussed completely.
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.
Make sure that the supply voltage is within the range of the rated value.
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.
Regulate voltage adjustment components on the power section until the +B the voltage reaches the rated value.
Test Point
Voltage (V)
Test Point
Voltage (V)
1 1 7 V ± 1 . 5 V
2 3 V ± 2 V
15 . 5 V ± 1 V
5 V ± 0 . 5 V
3 . 3 V ± 0 . 3 V
8 V ± 1 V
1 3 V ± 2 V
-1 3 V ± 2 V
1 9 6 V ± 2 V

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.
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.
Test Point
Voltage (V)
Negative of VD491
196± 2V
26± 1.5KV


27± 1.5KV

6.3± 0.3Vrms
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.