TB1238 – Schematic
Used Ics - TB1231N [video
chroma jungle], TMP87PS38N [System control], AT24C16 [memory], BSC25-02AW23
[FBT], TDA7057AQ [audio output], TA8427K [Vertical scan output]
The way go into the factory mode
1. Press the numeric keys, switch to the position 12
2. Press the numeric keys again, switch to the position 38
3. Press the MENU key to call up the POS.LOCK menu
4. Press the MUTE key
5. Press the numeric key to input the password 1, 2, 3, 8. Then the TV will enter into the factory mode while the "M" displayed on the top of the screen.
1. Press the numeric keys, switch to the position 12
2. Press the numeric keys again, switch to the position 38
3. Press the MENU key to call up the POS.LOCK menu
4. Press the MUTE key
5. Press the numeric key to input the password 1, 2, 3, 8. Then the TV will enter into the factory mode while the "M" displayed on the top of the screen.
Under adjusting mode, you can
select the item you want by pressing the Up/Dn
keys and you can adjust the value of the items when you press the
L/R keys.
Under adjusting mode, you can
select the item you want by pressing the “ ” keys and you can adjust the value
of the items when you press the “ ” keys.
Default
data
Note
1. The items with * in value are very special, do not adjust them at random. The items(1-5) are used to debug white-black-balance of set.
2. The general secret code is 2175.
3. If you find the threadlike disturbance on the top of picture, please adjust the VM 2 in the items and make its value come to 34.
4. When EPROM does not work, please exchange the same model chip with data that the manufacture has already input. 2
1. The items with * in value are very special, do not adjust them at random. The items(1-5) are used to debug white-black-balance of set.
2. The general secret code is 2175.
3. If you find the threadlike disturbance on the top of picture, please adjust the VM 2 in the items and make its value come to 34.
4. When EPROM does not work, please exchange the same model chip with data that the manufacture has already input. 2
Typical failures 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.
The detail checking and repairing steps are as follow.
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.
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:
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.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:
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 picture.
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.
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.)
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 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.
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:
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 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.
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 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.
The detail checking and repairing steps are as follow
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 CPU.
We can judge this failure by measuring the wave of the character in an oscilloscope.
The detail checking and repairing steps are as follow:
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 judge this failure by measuring the wave of the character in an oscilloscope.
The detail checking and repairing steps are as follow:
Full schematic: with pin
voltages
