Lenovo Y700-15ACZ Backlight problem

[hansdampf92]

Hi everyone.
I have an issue with my Lenovo Ideapad Y700-15ACZ.
A little while after replacing my screen (because i got a deep scratch in it), the eDP-Cable broke, probably shorting the pins for the backlight.

Apparantly it blew a fuse or some kind of 0 Ohm resistor.*
However i don't really have much experience with PCB, so i hoped you could help me identifying the damaged parts.

I attached a mainboard schematic i found on the internet.
But please note, this is for the Y700-14ISK, i have the AMD-Model (-15ACZ), but the layout should be almost identical. LCD Power Circuit is on Page 34.
I also attached an image of the underside of the eDP/Screen cable socket.

*Short explanation:
This model has LED-Backlight, so no inverter.
After getting a replacement cable, the backlight still didn't work, tested it on the old panel as well.
But there's clearly an image on the screen, you can barely see it with a strong flashlight.
Laptop also works perfectly fine when connected on an external monitor.
Problem has to be somewhere on the board

[Djosla]

Re: Lenovo Y700-15ACZ Backlight problem

make a picture of area around lcd connector...

based on schematic q33 could be bad but it`s not installed...you should check r17 ...Go back from 24,25,26 pins of lcd connector,you should be able to find it and check it`s resistance...

[hansdampf92]

Re: Lenovo Y700-15ACZ Backlight problem

Thanks for your answer!
Unfortunately i'm unable to trace the pins myself.
This eDP-connector has 20 Pins no the "boardside", but 30 Pins on the screenside, which makes it even harder for me to see what's going where.
I measured all the (obvious) resistors i could find on the board, they all seemed to have the right values.

I uploaded a pic of the connector area now, maybe someone can figure it out for me.

P.S.: My exact mainboard model is - BY 510 NM-A521 Rev 1.0, maybe someone has that schematic?

[jasko_jacker]

Re: Lenovo Y700-15ACZ Backlight problem

Thanks for your answer!
Unfortunately i'm unable to trace the pins myself.
This eDP-connector has 20 Pins no the "boardside", but 30 Pins on the screenside, which makes it even harder for me to see what's going where.
I measured all the (obvious) resistors i could find on the board, they all seemed to have the right values.

I uploaded a pic of the connector area now, maybe someone can figure it out for me.

P.S.: My exact mainboard model is - BY 510 NM-A521 Rev 1.0, maybe someone has that schematic?

On motherboard lcd connector measure pin 24-25-26 to check if +LED_VDD has a voltage and pin 23 DISPOFF#

[jasko_jacker]

Re: Lenovo Y700-15ACZ Backlight problem

Thanks for your answer!
Unfortunately i'm unable to trace the pins myself.
This eDP-connector has 20 Pins no the "boardside", but 30 Pins on the screenside, which makes it even harder for me to see what's going where.
I measured all the (obvious) resistors i could find on the board, they all seemed to have the right values.

I uploaded a pic of the connector area now, maybe someone can figure it out for me.

P.S.: My exact mainboard model is - BY 510 NM-A521 Rev 1.0, maybe someone has that schematic?

the schematic is not for your board, the right is:
https://***********/threads/y700-15a...nm-a521.18837/
but not for free

[hansdampf92]

Re: Lenovo Y700-15ACZ Backlight problem

the schematic is not for your board, the right is:
https://***********/threads/y700-15a...nm-a521.18837/
but not for free

Thanks, but i knew it's not the right schematic, i said that in my first post.
But the difference between those 2 models should be small (Y700-15ACZ vs. Y700-14ISK, released nearly at the same time, the boards look very similar, so i can't see a reason why they would completely redesign the LCD-Backlight-Circuit).

I already found that link before, but i'm not really willing to pay 10 Dollars to some obscure site, when i'm not even sure i'll be able to fix the problem with it.
I might eventually do that, when i'll understand what the actual problem is.
No offense.


Anyways, i measured the pins now.
Pins 4 and 5 have 20,5V
Pins 17 and 18 have 3,35V

The rest of the pins doesn't seem to have any voltage.
I guess the "signal" pins are supposed to have 0V when there's no display connected (i obviously disconnected the screen to measure the voltages, i dont see another way to do it).

[hansdampf92]

Re: Lenovo Y700-15ACZ Backlight problem

Hi,
so now i measured a few other things as well
The Pins on U9:
Pin 1: 3,3V Pin 2: 0V, Pin 3: 0V
Pin 4: 1,1V Pin 5: 3,3V

Any ideas what this means? :S

P.S.: I noticed the site you linked only has BIOS for my Board, but no schematics.

[dspok]

Re: Lenovo Y700-15ACZ Backlight problem

Can you let me know BL_PWM and BL_EN measurement on led panel?

[jasko_jacker]

Re: Lenovo Y700-15ACZ Backlight problem

Post the lcd model so I can search its pinouts

[hansdampf92]

Re: Lenovo Y700-15ACZ Backlight problem

Thanks!
First Panel was LTN156HL09-402, replacement is NV156FHM-N42, they're supposed to be identical.

[jasko_jacker]

Re: Lenovo Y700-15ACZ Backlight problem

First panel datasheet is not available for free, second panel only 41 and not 42, anyway should be the same pinout.
For backlight pin 22 (3.3v) and pin 23 pulse width modulation input

https://en.wikipedia.org/wiki/Pulse-width_modulation it's important to know what we do .

[dspok]

Re: Lenovo Y700-15ACZ Backlight problem

@hansdampf92

Check those pins as per datasheet jisko jacker posted.

[hansdampf92]

Re: Lenovo Y700-15ACZ Backlight problem

Hi, sorry that took so long.
So this time i had the display plugged in and measured the pins on the display itself.

I got Pins 12 and 13: 3,25V
Pin 17: 2,37V
Pin 22: 3,25V (went to 0V when i pressed FN+F2 - hotkey to turn of display backlight - , so it's working as it should)
Pin 23: -11mV
Pins 26-29: 20V

What would be a reasonable value for the PWM-Signal?

[dspok]

Re: Lenovo Y700-15ACZ Backlight problem

Pin 23 should be 3.3v
Put a jumper on pin 22 and pin 23 of display panel, see if backlight comes at full brightness.