Ics used:
TMPA8803/23/21 - Micro controller and small signal processor (UOC)
ST24C16-W – EEPROM
LA4267 - Sound power amplifier
LA78040 - Vertical scan output stage circuit
LC4053B/CD4053B - AV1/AV2 Switch
ADJUSTMENT PROCEDURE
Turn RP551 potentiometer to adjust B+ to specified voltage.
Check voltages for video out, vertical out, circuit work and audio power out as:
TV signal receiving
> Press MENU key, to select POS.MEMORY item.
Press V+ or V- key, to select SEARCH or AUTOMEMORY item, press P+ key to start searching.
> Press P+ or P- key to inspect the set if there is channel skipped, if so, searching again by SEARCH as above described.
> Press MENU key, to select POS.MEMORY item.
Press V+ or V- key, to select SEARCH or AUTOMEMORY item, press P+ key to start searching.
> Press P+ or P- key to inspect the set if there is channel skipped, if so, searching again by SEARCH as above described.
Inspection procedure
> Input the TV signal which system is designated in technical
specification
> Switch TV system to the set by pressing SYS key on user remote controller according to the TV system in SG. The picture and sound must be normal.
> Press TV/AV key, to select AV input. The picture and sound must be normal
> AV output inspection. Load a 75Ω resistor to VIDEO output terminal, 1Vp-p video output signal that is from TV signal should be observed on the oscilloscope. Load a 10K resistor to AUDIO output terminal, 0.7Vp-p audio output signal that is from TV should be observed on the oscilloscope.
> Switch TV system to the set by pressing SYS key on user remote controller according to the TV system in SG. The picture and sound must be normal.
> Press TV/AV key, to select AV input. The picture and sound must be normal
> AV output inspection. Load a 75Ω resistor to VIDEO output terminal, 1Vp-p video output signal that is from TV signal should be observed on the oscilloscope. Load a 10K resistor to AUDIO output terminal, 0.7Vp-p audio output signal that is from TV should be observed on the oscilloscope.
White balance adjustment
> Receive the monoscope pattern signal.
> Press G (G.DRIVE) key and B (B.DRIVE) key on No.1 service remote controller to select G-DRV and B-DRV respectively, then press + or – key to adjust the white balance at the directed value (which is according to the specification of factory’s adjustment)
> Press R+ or R-, G+ or G- and B+ or B- key respectively to adjust the white balance of low light until the white balance of high and low light is good.
> Press G (G.DRIVE) key and B (B.DRIVE) key on No.1 service remote controller to select G-DRV and B-DRV respectively, then press + or – key to adjust the white balance at the directed value (which is according to the specification of factory’s adjustment)
> Press R+ or R-, G+ or G- and B+ or B- key respectively to adjust the white balance of low light until the white balance of high and low light is good.
Troubleshooting
Three-None (no raster, no picture, no sound)
This failure is mainly caused by big-power circuit such as power supply, horizontal scanning, vertical scanning.
This failure is mainly caused by big-power circuit such as power supply, horizontal scanning, vertical scanning.
Two-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.
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.
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.
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.)
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 cannot 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.
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 cannot 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.
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 TMPA88XX circuit, the clock pulse is generated by pin6 / pin7 of N204 and 8M crystal oscillator.
Television remote-control system also needs reset circuit that can preset the values in internal register. The circuit around pin6 of N204 is called auto-reset circuit. If UOC detects errors in resetting, it will come to the state of program protected.
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 TMPA88XX circuit, the clock pulse is generated by pin6 / pin7 of N204 and 8M crystal oscillator.
Television remote-control system also needs reset circuit that can preset the values in internal register. The circuit around pin6 of N204 is called auto-reset circuit. If UOC detects errors in resetting, it will come to the state of program protected.
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 fly-back pulse signals do not come to UOC.
We can judge this failure by measuring the wave of the character in an oscilloscope.
This failure is usually cause by the circuit of character generated and located. Most of reasons are that the horizontal and vertical fly-back pulse signals do not come to UOC.
We can judge this failure by measuring the wave of the character in an oscilloscope.
SCHEMATIC
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