blank laptop screen B156XTN02.0

[caspian]

Dear Technicians,

I have got a Dell inspiron 5520 laptop with B156XTN02.0 internal screen.
The laptop displays normally on external monitor.
When I turn the laptop on, I see blank on the internal screen, but the screen backlight turns on and works normally.
The screen is not white. it is just on but there is no text/image on the screen.

I measured voltage on the LVDS connector on the laptop motherboard.
It seems all the power and signal pins have proper voltages.

Then, I measured probe points on the screen's tcon board.
I discovered that there are proper voltages present on most the probe points including Vin, Vcom, V_25, VGH, AVDD, IVPP, LED_En, VGMA1.
but the following probe points seem suspicious:
IMG_En = 0 v
Reset = 3.1 v
POL_En = 0 v
DCR_En = 0 v

now please explain what is faulty that led to the blank screen and how to fix it.

I attached internet images of the tcon board.
The tcon IC is AUO-11307 which is missing in the images at place(2) but it exists on my tcon board.

notes:
I do not have another screen to replace.
I do not have another laptop to test the screen.
The fuse on the tcon board is OK.
I did not measure AUO-11307 because I have not found its datasheet and its pinout.

thanks

[piernov]

Re: blank laptop screen B156XTN02.0

You must first make sure that either one of the laptop or the panel is the issue. We could be troubleshooting the panel for ages when it's in fact the motherboard which is the source of your problem. If the panel is not broken, is powered on and shows only a black screen, it's likely that it is a motherboard issue (or it could be a cable issue).

[caspian]

Re: blank laptop screen B156XTN02.0

I forgot to say that my laptop motherboard is new and the screen comes from a water-damaged laptop.
but no water entered the screen when it happened. only the previous laptop motherboard got water-damaged.

I stored the screen for a year under an 80% relative humidity.
so I think the tcon IC may be faulty.
I use a non-genuine AC adapter for the laptop, but display is OK on external monitor.

Is it probable that the tcon IC become faulty?

[caspian]

Re: blank laptop screen B156XTN02.0

I tested the video cable and it has no disconnection
there are voltages on output data signals of motherboard.
I do not know why IMG_En has 0v on the tcon board.
Anybody knows when IMG_En becomes 0v?

[caspian]

Re: blank laptop screen B156XTN02.0

I note that the screen is not completely black. it turns on with backlight on but nothing is displayed. In addition, the screen is not much white. it is just a bit bright as it should be in command-line view.

[ramneb]

Re: blank laptop screen B156XTN02.0

It could be the culprit is the circuit board on your LCD has a problem.

[alvin24705]

Re: blank laptop screen B156XTN02.0

Dear Technicians,

I have got a Dell inspiron 5520 laptop with B156XTN02.0 internal screen.
The laptop displays normally on external monitor.
When I turn the laptop on, I see blank on the internal screen, but the screen backlight turns on and works normally.
The screen is not white. it is just on but there is no text/image on the screen.

I measured voltage on the LVDS connector on the laptop motherboard.
It seems all the power and signal pins have proper voltages.

Then, I measured probe points on the screen's tcon board.
I discovered that there are proper voltages present on most the probe points including Vin, Vcom, V_25, VGH, AVDD, IVPP, LED_En, VGMA1.
but the following probe points seem suspicious:
IMG_En = 0 v
Reset = 3.1 v
POL_En = 0 v
DCR_En = 0 v

now please explain what is faulty that led to the blank screen and how to fix it.

I attached internet images of the tcon board.
The tcon IC is AUO-11307 which is missing in the images at place(2) but it exists on my tcon board.

notes:
I do not have another screen to replace.
I do not have another laptop to test the screen.
The fuse on the tcon board is OK.
I did not measure AUO-11307 because I have not found its datasheet and its pinout.

thanks

if MB can be display on monitor so power squence it's ok, no need check to power on strukturu MB.
the problem is on display LVDS.

see my attach picture.

if the RED selected by me and Green selected its ok, so u must be check to ur LCD, not ur MB.

[caspian]

Re: blank laptop screen B156XTN02.0

are the following voltages ok on the screen connector on the laptop mainboard:
pin1: LVDS_A0- = 1.7v
pin2: LVDS_A0+ = 0.05v
pin4: LVDS_A1- = 1.7v
pin5: LVDS_A1+ = 0.05v
pin7: LVDS_A2- = 1.7v
pin8: LVDS_A2+ = 0.05v
pin10: LVDS_ACLK- = 1.5v
pin11: LVDS_ACLK+ = 1.5v
pin27: INV_PWM = 1v
pin28: DISSOFF = 3.3v
pin36: LCDVDD = 3.3v
pin37: 3.3v
pin40: 19v

[newfoxinformatica]

Re: blank laptop screen B156XTN02.0

Pin27 very low correct is 3.3v or 19v new project

[piernov]

Re: blank laptop screen B156XTN02.0

Pin 27 "INV_PWM" is a PWM signal for backlight brightness, doesn't matter here and should be OK.
If you have 3.3V after the fuse on the T-Con board, then yes most likely one of the T-Con board's IC is bad. This still does not rule out a bad motherboard though.
On some of those board there will be a voltage regulator (LDO, 1117-like), but I don't see any on this board. However there are some inductors, there must be a voltage there.
You can check for short to ground on capacitors (it can be either the cap itself or an IC).
Anyway, it's probably not repairable.

[caspian]

Re: blank laptop screen B156XTN02.0

is this normal that there is 0.05v on LVDS_A0+?
should it have a higher voltage?

[caspian]

Re: blank laptop screen B156XTN02.0

the problem is solved.
it was the video cable that was not properly plugged into the LVDS connector on the motherboard.
thanks for the responses.

[koka0011]

Re: blank laptop screen B156XTN02.0

check major panel volteges like vgh/voff/vcom/avdd
it could be a problem with level shifter ic or corrupted flash rom.change the rom ic first.