Re: Viewsonic vx2252mh
Hi SolomonMan,
White screen issue typically means either LVDS connection problem or T-con board power supply problem. Since you already more or less eliminated the LVDS connector as the problem, that leave the T-con board power supplies. So let's get you on the right foot with some basics on that.
The T-con board generates several voltages (i.e. contains internal power supplies) that are used for driving the TFT, along with powering the drivers and LVDS transcoder IC.
The first/main voltage is typically a 3.3V to 5V supply from the main board (sometimes called "Vcc", "Vdd", "3V3", or "5V1" on test points - the notation varies between monitors and is not consistent.) This is what connects to your "F1" fuse and powers everything else on the T-con.
The second voltage is generated (through a boost regulator) from the first/main voltage above and is typically in the range of 10 to 15V. Most T-con boards call it "AVDD", but again, the notation may vary. You will find this rail usually near a round inductor and a large diode.
The 3rd and 4th voltages are generated from "AVDD" mentioned above via charge-pump method. Many T-con board often refer to them as "VGH" and "VGL" (though sometimes also "VG_ON" and "VG_OFF".) VGH is typically +15 to +32V depending on the monitor, and is what is used to turn "On" the transistors in the TFT panel. VGL is a negative rail usually in the range of -5 to -10V. It is used for driving transistors Off in the TFT panel.
Apart from the 4 voltages / power supplies on the T-con mentioned above, there may be a few more for various other functions. Usually, the "big chip" on the T-con is what decodes the LVDS signals from the main board, and this chip may require 1.8V, 2.5V, or 3.3V (or a combination of these). So depending on its requirements, you may see up to 3 more dedicated voltage regulators (typically linear ones, like 1117 or 1084) near that chip.
Worth noting here, at least from my experience, is that these (usually linear) supplies rarely fail. The ones that fail most often are AVDD, followed by VGH and VGL. In fact, if AVDD fails, VGH and VGL cannot be generated. The cause of the failure for these supplies is usually "shorted" ceramic capacitor(s). And by shorted, I've had some ceramic caps show as much as 30-40 Ohms. Either way, when something goes wrong with these supplies, the fuse almost always blows.
So with all of that said, see if you can find any test points on your T-con that mention names similar to what I noted above. If you can, set your multimeter to the lowest resistance scale (200 Ohms) and measure between those test points and a ground. Make sure the T-con is well grounded before this, so we get accurate measurements. After that, post what results you get here. (I'm willing to bet there is a shorted/bad ceramic cap on the AVDD rail.)
If you can't find the above test points, please post another picture with more detail around that "AUO" chip that is seen on this picture:
https://www.badcaps.net/forum/attach...1&d=1581047773
I would also like to request a more detailed picture from the area around the fuse / LVDS cable.
An alternative way to finding if the issue is caused by a shorted cap is to first measure resistance across all of the larger ceramic caps. Any that show less than 100 Ohms, note/mark them down, as one of them could be bad. (You will find that many of these larger ceramic caps are in parallel, so if one reads a certain resistance, so will any other caps in parallel with it. This means if you stumble across a ceramic cap that appears to be shorted, it may actually be another ceramic cap on the board elsewhere that is making the one you are currently measuring as showing shorted. So just keep that in mind when doing measurements.)
"U" prefix is indeed used for ICs (through some manufacturers will also use "IC" instead.)
"B" is typically used to mean "Ferrite Bead... or simply, an inductor with a very tiny inductance.
"O".... not sure I have seen that before anywhere. Perhaps you mean "Q"? In that case, this would indicate a transistor (BJT, MOSFET, IGBT, and etc.)
"T" is used for transformer.
"L" is inductor.
Hi SolomonMan,
White screen issue typically means either LVDS connection problem or T-con board power supply problem. Since you already more or less eliminated the LVDS connector as the problem, that leave the T-con board power supplies. So let's get you on the right foot with some basics on that.
The T-con board generates several voltages (i.e. contains internal power supplies) that are used for driving the TFT, along with powering the drivers and LVDS transcoder IC.
The first/main voltage is typically a 3.3V to 5V supply from the main board (sometimes called "Vcc", "Vdd", "3V3", or "5V1" on test points - the notation varies between monitors and is not consistent.) This is what connects to your "F1" fuse and powers everything else on the T-con.
The second voltage is generated (through a boost regulator) from the first/main voltage above and is typically in the range of 10 to 15V. Most T-con boards call it "AVDD", but again, the notation may vary. You will find this rail usually near a round inductor and a large diode.
The 3rd and 4th voltages are generated from "AVDD" mentioned above via charge-pump method. Many T-con board often refer to them as "VGH" and "VGL" (though sometimes also "VG_ON" and "VG_OFF".) VGH is typically +15 to +32V depending on the monitor, and is what is used to turn "On" the transistors in the TFT panel. VGL is a negative rail usually in the range of -5 to -10V. It is used for driving transistors Off in the TFT panel.
Apart from the 4 voltages / power supplies on the T-con mentioned above, there may be a few more for various other functions. Usually, the "big chip" on the T-con is what decodes the LVDS signals from the main board, and this chip may require 1.8V, 2.5V, or 3.3V (or a combination of these). So depending on its requirements, you may see up to 3 more dedicated voltage regulators (typically linear ones, like 1117 or 1084) near that chip.
Worth noting here, at least from my experience, is that these (usually linear) supplies rarely fail. The ones that fail most often are AVDD, followed by VGH and VGL. In fact, if AVDD fails, VGH and VGL cannot be generated. The cause of the failure for these supplies is usually "shorted" ceramic capacitor(s). And by shorted, I've had some ceramic caps show as much as 30-40 Ohms. Either way, when something goes wrong with these supplies, the fuse almost always blows.
So with all of that said, see if you can find any test points on your T-con that mention names similar to what I noted above. If you can, set your multimeter to the lowest resistance scale (200 Ohms) and measure between those test points and a ground. Make sure the T-con is well grounded before this, so we get accurate measurements. After that, post what results you get here. (I'm willing to bet there is a shorted/bad ceramic cap on the AVDD rail.)
If you can't find the above test points, please post another picture with more detail around that "AUO" chip that is seen on this picture:
https://www.badcaps.net/forum/attach...1&d=1581047773
I would also like to request a more detailed picture from the area around the fuse / LVDS cable.
An alternative way to finding if the issue is caused by a shorted cap is to first measure resistance across all of the larger ceramic caps. Any that show less than 100 Ohms, note/mark them down, as one of them could be bad. (You will find that many of these larger ceramic caps are in parallel, so if one reads a certain resistance, so will any other caps in parallel with it. This means if you stumble across a ceramic cap that appears to be shorted, it may actually be another ceramic cap on the board elsewhere that is making the one you are currently measuring as showing shorted. So just keep that in mind when doing measurements.)
Originally posted by SolomonMan
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"B" is typically used to mean "Ferrite Bead... or simply, an inductor with a very tiny inductance.
"O".... not sure I have seen that before anywhere. Perhaps you mean "Q"? In that case, this would indicate a transistor (BJT, MOSFET, IGBT, and etc.)
"T" is used for transformer.
"L" is inductor.
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