Talking about how to properly repair the TV (1) the impact of SDA, SCL on the circuit - News - Global IC Trade Starts Here.

How to properly repair the TV (1) The impact of SDA and SCL on the circuit To repair the TV, we must grasp the essence of the fault, in order to be targeted, how to grasp the essence of the fault requires corresponding theoretical knowledge and rich practical experience. . Here are a few examples to analyze the nature of the fault, to avoid detours, quick maintenance, scientific maintenance, and rational maintenance. At the same time, everyone is welcome to participate and discuss together.
Case, Toshiba 29VH9UC, boot raster size changes, similar to +B voltage instability.
The machine is a digital high-definition machine, the image processing circuit is processed by the so-called 03 box. The common problem of the machine is that the 03 box is easy to open and weld, resulting in image aberration, and at the same time causing SDA and SCL voltage to be abnormal, which affects the work of the line and the field, resulting in Raster exception, understand this, then it should not be difficult to deal with the fault. First, you should remove the 03 box and turn it on again. At this time, the fault of the raster size change should disappear.
The repair process also verified my inference, repair welding 03 digital box, troubleshooting.
What needs to be explained here is that the current TV sets are basically controlled by SDA, SCL, and the voltage of SDA and SCL are basically externally connected to each control unit (each integrated block, such as the row drive block, decoding). The power supply on the block, etc. is maintained. If one of the SDAs, the power supply of the DCL plug-in unit disappears or the abnormal operation will inevitably lead to the SDA, the SCL voltage is lowered, resulting in a fault.
Here, by the way, a forum for help posts, Toshiba 34VH9UC, the image moves down, it seems that the grating is only half, the helper tangled field circuit maintenance, the replies are also pay attention to the field of power supply, and so on, in fact, the nature of the fault is also The SDA, SCL is abnormal, and the SDA, SCL malfunction should be its plug-in unit, the biggest suspect is still 03 boxes, of course, it may be SDA, SCL plug-in tuner, Liyin box, etc. The SDA and SCL of each unit should be disconnected one by one until troubleshooting.
The correct maintenance method for this example is to remove the 03 box and turn it on. If the grating is normal, it must be 03 box of solder joints.
This is the original post of the help:
Helper: The top half of my Toshiba 34VH9UC TV screen is a black screen. The bottom half of the screen is compressed to the bottom. Moreover, the image frequency of the lower half is still unstable, and the images on the left and right sides are still Indented inward. The machine is automatically turned off for half a minute, and the field scanning part that I checked also replaced the integrated circuit TA1317AN integrated block and the LA7833 integrated block, and also replaced the five large capacitors on the periphery of the integrated block. No repairs, please give pointers to the master answer: Is the power supply normal? Check the resistance of the DC feedback circuit of the pillow school and the field output circuit.
Answer B: Replace the filter capacitor on the periphery of the field.
C Answer: You did not explain how much voltage is in each part of your machine, because it is not normal at the same time, and it is related to power supply.
Ding replied: You can fix this, first remove the 03 box, the 03 box is the digital board, and then turn it on. At this time, the screen should have a blue screen, but there is no image, because the image processing part is in the digital box, if the grating returns to normal, it should be There is a problem with the removed digital box, which can be repaired. . I will go to this step. .
E: Answer: Is the power supply normal? Check the resistance of the DC feedback circuit of the pillow school and the field output circuit.
Ding replied: I am afraid that this kind of maintenance will not work. The field is not normal and will affect the pillow school circuit. The field has SDA in the similar machine. SCL controls the field width, field linearity and field center. The nature of the fault is in SDA, SCL, and the maximum may be digital. Box soldering causes SDA, SCL often, you can disconnect the SDA, SCL of the digital box, so the field should return to normal. . . . Maintenance failures should be based on phenomena, and pillow schools should not be considered. .
. . . .
As you can see, Ding is my own.

Another example, Hisense HDP2908N, boot black screen, showing a crash state, improve the acceleration of the visible white grating, the analysis should be the failure of the digital board, measured SDA, SCL voltage is low, it is estimated that the digital board Liyin block fault, broken The SDA of the TDA7442D, the isolation resistance of the SCL, the image returns to normal, and the SDA and SCL voltages return to normal. It is obviously SDA. The SDA external unit TDA7442D fails to work, resulting in SDA and SCL voltage drop.