toshiba satellite c855-1kx no picture lcd

[babeloued]

hello
i have toshiba satellite c855-1kx no picture on lcd but ok vga
the screen lcd is ok because it s new so i try to do some test on motherboard and i realise no vcc on board but no vcc to screen too ,the cable lvds is ok ,it s a new one
motherboard is H000050770
please can i have some help

[JaroTech]

Re: toshiba satellite c855-1kx no picture lcd

Hi, provide the schematics of your board.

[babeloued]

Re: toshiba satellite c855-1kx no picture lcd

hi
i don t have excatly the true schematic but approximative
https://www.badcaps.net/forum/attach...1&d=1457544554

[JaroTech]

Re: toshiba satellite c855-1kx no picture lcd

Do you mean that you don't have LCDVCC on pins 37,38 ?

[babeloued]

Re: toshiba satellite c855-1kx no picture lcd

yes ,anything 37 ,38 and on lcd board too

[JaroTech]

Re: toshiba satellite c855-1kx no picture lcd

If you look at page 25, if it's similar, you have the U1 chip that powers the LCD. If you have this chip, measure the voltages for all the pins.

[babeloued]

Re: toshiba satellite c855-1kx no picture lcd

it look like not the same ,i realise the schematic is no good,i have a chip near the lvds connector who have 5 pins and not 6 pins like U1 and is connect to this 40 pins connector
could i have the true schematic,if anybody have it .thanks

[babeloued]

Re: toshiba satellite c855-1kx no picture lcd

chip with number 52444

[JaroTech]

Re: toshiba satellite c855-1kx no picture lcd

Can you take a good picture so that we can read the number on the chips in the LCD connector area?

[babeloued]

Re: toshiba satellite c855-1kx no picture lcd

chip have the number 52444
i try today to reflow the graphic amd chip with hot air but now i don t have any picture not in vga or lcd
so too bad for mee

[piernov]

Re: toshiba satellite c855-1kx no picture lcd

Never reflow a GPU, it will most likely die.
If the GPU is known to be from a defective series or if it doesn't work at all, you may try to heat it up to 200°C for a couple of minutes (*that's not a reflow*), but that should not be done systematically.
If the issue is no display on internal but display ok on external, you've to figure out if it's actually the GPU at fault or not before messing with the GPU itself.
On modern platforms the screen need to be detected (reading EDID on the I2C bus) and the GPU (or PCH depending on what the LCD is actually connected to) gives the signal to turn the LCD power on, but there are a couple (or more) of transistors between the power on signal and the actual power at the LCD connector. This needs to be traced to know whether the issue comes from the GPU (or maybe the BIOS) or the discrete components for LCD power.