For those who have been doing LCD/LED repairs will agree with me that screen issues are very common and are almost always caused by the small circuit usually located on the top of LCD panel as the major cause of these problems.
These issues are quite common and therefore a tech without adequate knowledge on how this circuit works will have it tough on his workbench.
Besides having it rough will also part with less profit since most of the television will be send back to the sender for lack of repair.
The most effective way of troubleshooting is voltage testing, in this article I am going to look at critical t-con voltages and what happen if they fail.
1.Vin/Vcc…. Usually 3v, 5v or 12v, and from the main board and the best place to test this voltage is before and after the fuse on the t-con board next to the connector to the main board.
If this voltage is missing there will be no display but the backlight will be on.
2. VON/VGH/VGON/VGGG…. this voltage is between 20v -30v and is generated by the dc-dc ic.
Test point is usually marked on the board.
If this voltage is missing slow motion picture will occur.
3.VOFF/VGL/VGOFF/VEEG…. This voltage is between -5 and -10 volts depending on size. Also generated by the dc-dc ic.
If this voltage is missing, white display will appear.
4.VDD/Vlogic/Vddd/Dvdd…. usually 3.3v and it from dc-dc ic or regulator.
If the 3.3 volts is missing, white display will appear.
If 1.8v voltage is missing, white display will lines will appear on the screen.
5.VDA/Avdd/Vdda/Vsource….this voltage is between 13v-20v and also from dc-dc ic.
If this voltage is missing white display will occur or display full of vertical color lines/bars.
6.VGH…This voltage is usually between 20v-30v and its from dc-dc ic.
If this voltage is missing, slow motion picture will occur.
7.Vcom…. this voltage is between 5v - 7v
If this voltage is missing negative picture will occur.
8.VGM…gamma voltages, these are many and always in descending manner eg V17……v1
If these voltages are missing as in gamma ic is not working then white display will appear immediately.
Mainboard or t-con problem, how do i isolate between t-con or mainboard problem?
Press menu button from the remote or front keys…. if the OSD is okay then the problem is the main board, or LVDS cable.
You can learn more about LED television repair from this book By Humphrey Kimathi. click here or the book cover below.