POWER SUPPLY [SMPS] CIRCUIT. {Click on pictures to Enlarge}
- This failure is mainly caused by big-power circuit such as power supply, horizontal scanning, vertical scanning.
- The detail checking and repairing steps are as follow.
None (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.
- Before checking these circuits, a kind of practical test method is introduced. It is called “Signal-input way ”. The detail is described as follow: 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.
- Note: In the TV test, we mainly observe the noise wave on the CRT and listen to the noise voice liking as “Ka…..Ka” from the loudspeakers.
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. The detail checking and repairing steps are as
follow.
Note: Before repairing, assure that the volume is on and the
state of set is in “TV.
Only horizontal line in the middle of the screen:
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.)
Only vertical line in the middle of the screen
This is a dangerous failure. It probable causes flashover
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:
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:
- 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 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 programmer protected.
- 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.
