- This failure is mainly caused by big-power circuit such as power supply, horizontal scanning, and vertical scanning.
- The detail checking and repairing steps are as follow.
NO PICTURE - NO SOUND
- The failure shows that the set does not display the picture but it has noise wave or blue background or OSD on the screen. This means that the circuits of power supply, horizontal scanning, vertical scanning and video amplification are normal and they are not considered in the repairing. The failures are mainly in the small signal processing circuits.
- We can use the resistance function of an analog multimeter, connect the red pole (negative in ohm scope) on the circuit board ground, then touch softly the test point with another pole (black pole) in ohm scope meanwhile observe the reactivity on the output device.
No Picture
{Click on charts to Zoom}
No Sound
- In this kind of failure, first of all we should observe if there is the picture on the CRT . It proves the small signal circuit to work correctly with the picture on the CRT and we only check the sound signal processing and sound amplification circuit. The repairing method (B1) may be referred without picture.
Note: Before repairing, assure that the volume is on and the state of set is in TV.
ONE HORIZONTAL LINE ACROSS THE MIDDLE OF THE SCREEN
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If vertical deflection circuit does not work, this kind of failure will happen. In deflection yoke, there only has horizontal sweeping. The electron beam in the CRT only moves in the horizontal orientation so form this failure. (While checking horizontal and vertical deflection circuit s failure, we have better to use an oscilloscope.)
ONE VERTICAL LINE DOWN THE MIDDLE OF THE SCREEN
This is a dangerous failure. It probable causes flash-over and smoking inside the set. Don t let your TV work for a long time as this failure appears. Because the electron beam can not move in the horizontal orientation, the failure should be in the horizontal deflection circuit. We mainly check the open-circuit fault in horizontal deflection circuit. The detail checking and repairing steps are as follow:
CPU 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:
- The power supply: In general, it is 5V, the error is not above 10% and the disturbance pulse is as small as possible.
- The clock pulse: In TB 1238 circuit, the clock pulse is generated by pin31/ pin32 of N701 and a 8M crystal oscillator. Television s remote-control system also needs reset circuit that can preset the values in internal register. The circuit around pin33 of N701 is called auto-reset circuit. If CPU detects errors in resetting, it will come to the state of program protected.
NO 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 CPU. We can make sure about this failure by measuring the wave of the character in an oscilloscope.
The detail checking and repairing steps are as follow:
