Service manual

22
Model No: 21WHS3-Bn
Version 1.0
E UOC does not work
In television, remote-control system is similar with the computer system. In theory , it can work if it holds two conditions as follow:
1. The power supply: In general, it is 5V, the error is not above 10% and the disturbance pulse is as small as possible.
2. The clock pulse: In TDA93XX circuit, the clock pulse is generated by pin58 / pin59 of N301 and 12M crystal oscillator.
Television’ s remote-control system also needs reset circuit that can preset the values in internal register. The circuit around pin57
of N204 is called auto-reset circuit. If UOC detects errors in resetting, it will come to the state of program protected.
The detail checking and repairing steps are as follow:
F No OSD (On Screen Display)
This failure is usually cause by the circuit of character generated and located. Most of reasons are that the horizontal and vertical flyback pulse signals do not come to UOC.
We can judge this failure by measuring the wave of the character in an oscilloscope.
The detail checking and repairing steps are as follow:
3V
＜
3.3V
=14V
＜
3.3V
YES
=3.3V
NO
＜
3.3V
3.3V
N301 does not work
The voltage on the pin 56 of N301
Observe if there is sine wave on the pin 58 or pin 59
of N301 with an oscilloscope
Check the voltage on the positive pole of C548
NO
YES
3.3V
3.3V
Check alternant voltage on secondary coil of N505,
Check X761, N301
Check R561,VD564
Check the voltage on the pin 54 of N301
Check T501, VD522,R565
Check N301
Check the voltage on the emitter of VD564
Check the voltage on the positive pole of VD522
Check VD522, T501
Check R565,R546,N505
Check L752,L753
YES
NO
Check FBT T451
No OSD
Check the wave on the pin 7 of FBT
Check C482, R485, VD483, R487, N301