General question about LVDS voltages. Blank Backlit Screen.

[triplefour]

im trying to understand how mainboards send data to tcons and tcons send data to panel boards and how panel boards control the panel itself.

but starting at the beginning: if i have a tv with symptom: blank backlit screen, i want to verify if the mainboard is functioning properly first. its easy to see if its sending 12v to the tcon...but im pretty foggy on what the other lines of the LVDS connector should have on them.
and also should they have the same voltages on them regardless of if the t-con is connected?
and also how do you probe these pins easily? they are so close together it is
quite risky even with a fine needle point.

i tried scratching away some of the solder mask to get at the copper traces to probe them but when i did, i didnt see any voltages there.
i had the TV running and displaying a moving picture so i thought
i would see something on those "data lines"
but admittedly i dont know much about what these lines are.
i know it probably varies from brand to brand but im assuming theres some commonalities as well.
is there a good guide to this somewhere?

these pictures are from a vizio i have that has a damaged panel but still shows some image so i figured its good for learning on.

[diif]

Re: General question about LVDS voltages. Blank Backlit Screen.

You can use a oscilloscope to check the lines for signalling.

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

You can use a oscilloscope to check the lines for signalling.

i dont have an osciloscope... can you explain why i would need this to see any voltage here?

[Davi.p]

Re: General question about LVDS voltages. Blank Backlit Screen.

panels checkout is possibly made by connecting only power supply line to tcon, if it has at least a flash mem on it i guess, it will show an auto test, video signals from mb are sent serially and parallely on differential couple of lines, search Wikipedia for differiential signal, its pretty clear to read, the rgb + clock data are sent sequentially in parallel groups. from tcon to panel there are similar signals, the video data enters the source drivers sequentially and parallely, in some panels it is transferred 2 pixels per clock cycle, the source cofs are cascaded, so input signals enters the first cof and then are transferred the the final one sequentally, the signals inputs a shift register that fills the internal byte that is converted to analog value , shifted to another voltage level and sent to the column..

[CapLeaker]

Re: General question about LVDS voltages. Blank Backlit Screen.

Hmm. Yeah… I guess you got to do some reading on how LVDS a works. I use a 100MHz Oscilloscope and that works just fine for that. Basically you want to change something on the screen, like turning the OSD of and on all the time and probe the differential pairs and look for a change on the oscilloscope screen. That trick works A1.
As for LVDS voltages, they would be very low. Something like 350mV. Problem with it is, that you can’t 100% identify a problem let’s say a main board that doesn’t send anything to the tcon. It’s much easier to probe the LVDS with an oscilloscope.

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

What do you mean by differential pairs? Do I have to probe 2 lines at once? Gonna order an oscilloscope soon. Other problem is physically how to probe the pins of the lvds connector? They are very close together and the danger of shorting two pins next to each other is too great.
..but is there any way in the meantime to diagnose without an osciloscope when we have blank backlit screen whether its mainboard, tcon, or panel?

[Davi.p]

Re: General question about LVDS voltages. Blank Backlit Screen.

you can't do without screen tester or screen autotest!

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

you can't do without screen tester or screen autotest!

what is this screen tester? is this a tool i can buy?

same question for autotest

[vinceroger69]

Re: General question about LVDS voltages. Blank Backlit Screen.

what is this screen tester? is this a tool i can buy?

same question for autotest

Maybe something like this ? https://www.aliexpress.com/item/3268...d=qAzms40By4uF

[lotas]

Re: General question about LVDS voltages. Blank Backlit Screen.

Or such a board tester.
https://aliexpress.ru/item/328202796...00023851290229

[diif]

Re: General question about LVDS voltages. Blank Backlit Screen.

Working link without the tracking. https://aliexpress.com/item/32820279611.html

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

wow why is the motherboard tester 450$ and the panel tester is only 62? very interesting devices... ill have to look into more. definitely cant be dropping no 450$ any time soon though!

[Davi.p]

Re: General question about LVDS voltages. Blank Backlit Screen.

repeat from post 4 , panels checkout is possibly made by connecting only power supply line to tcon, disconnecting lvds cable, this if it has at least a flash mem on it i guess, it will show an auto test,

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

repeat from post 4 , panels checkout is possibly made by connecting only power supply line to tcon, disconnecting lvds cable, this if it has at least a flash mem on it i guess, it will show an auto test,

interesting. if i read this right, some TCON have a self test ability, if you give them no signal from the mainboard but just provide them with 12v from the psu directly...like to the fuse on the TCON? and have it connected to the panel then it may show a test pattern?
definitely have to try this on some junker TVs i got lying around.


definitely also want to buy all the tools i dont have yet.
oscilloscope
panel tester
flir camera
esr meter
probably something else too

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

Maybe something like this ? https://www.aliexpress.com/item/3268...d=qAzms40By4uF

so i ended up buying this thing...and it comes with no manual! there seems to be instructions printed on the device itself but its all in chinese!
i tried to google up a manual but so far havent found anything. oh boy!
it looks awesome...just have no idea how to use it!
after powering it on it displays the number 23 which according to the chart is 1920 x 1080 which makes sense but up in the top left it shows panel voltage and the red led is lit indicating 3.3v but i cant figure out how to change it to 5 or 12. the buttons on the left change the number in the 2 digit LCD but the buttons on the right dont seem to do anything. there is a power button which turns on a red power LED. there are cables that hook up to various T-CON connections, but in the instance of a tv im thinking to hook it up to, there are 3 different connectors that all fit but have different pinouts..so i need to know something about these panels before plugging anything in, im thinking?

quite confusing. maybe i can use some app to translate these instructions.
edit: google translate works really well and i think i understand how to use this device now. you long press the auto button to switch panel voltages, and once you connect and press power button to send power to t-con, then pressing the buttons on the right side change the test pattern.
but i still dont quite know how to tell which connector to use to connect to the tcon.

[Lee M.]

Re: General question about LVDS voltages. Blank Backlit Screen.

back to your original problem, blank backlit screen. I had the same problem. I unplugged one of the ribbon cables going from the tcon to the panel driver boards. Turned on the set and got half of the screen looking perfect. Try unplugging one cable and if that doesn't work plug it back in and try unplugging the other one. If u get half a pic that eliminates the main board. I think my problem is a short on the driver board causing the blank screen. Next I'll try checking the surface mount caps on the driver board for a short.

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

yeah i always try one cable disconnected, then the other one. sometimes u dont get picture on either side. but sometimes this may just be how that particular tv works? some detect that both sides are not plugged in and then dont send any image? pretty sure there is no 100% rule here.

[triplefour]

Re: General question about LVDS voltages. Blank Backlit Screen.

translated images for anyone curious as to what it says on this thing