Fix Your Stuff Community Store

Free Shipping on Domestic Orders $75+

1 Question View | 11 Parts Shop

Options

Backlight Issue, work done on it already

I’m experiencing an issue with a 2nd hand Lenovo Yoga 7 14ARB7 82QF.

Bought it as faulty with a no backlight on main display and I figured it would be an easy fix. I had gotten a new LCD screen and after replacing it, the fault remained. The HDMI works fine and displays well.

I have tried looking for fuses on the main board but it is not very obvious where these fuses are. I can’t see any shorts on what I think is the backlight circuit.

Other suggestions are to do bios updates and driver updates but no luck.

Would there be any schematics out there or possibly some people who have been able to overcome this issue?

Answered! View the answer I have this problem too

Is this a good question?

Yes No
Score 0
2 Comments

HI @saschawestpfahl

What is the model number of the motherboard e.g. NM-E021 or similar, which is printed on the board?

by

Hi @jayeff

It is NM-E671

by

Add a comment

1 Answer

Filter by:
Most Helpful Newest Oldest
Chosen Solution

Options

Hi @saschawestpfahl

Unfortunately I can't find any downloads online (free or paid) for the schematics (or a boardview file) for an NM-E671.

Just verifying that you got the correct replacement LCD panel i.e. same Lenovo part number (usually found on the back of the LCD panel) as the original LCD panel?

Asking because looking at the parts list (click on Select Commodities > LCD Assemblies (4) there is an OLED LCD module in the list of LCD panels (the other IPS panels all have LED backlighting) and none of them can be used as substitutes for any of the others that are used. My understanding of OLED panels is that they don't have LED backlighting as the OLED pixels provide their own lighting.

If the replacement panel is the correct panel, (hopefully it's an IPS panel as I don't know much about OLED panels) with the laptop turned on etc and with no external monitor connected i.e. black screen on laptop, try shining a torch at an angle close to the laptop screen and check if you can see any images on the screen. They will be very faint if they are to be seen so trying this in a darkened room may help.

If you can see images then there is a backlight problem, either a faulty backlight power supply or a faulty EDP cable between the motherboard and the LCD screen

There is always backlight power (+LEDVDD) being supplied to the LCD panel. It is a signal sent on the dispoff (aka bklen) lead that is used to turn the backlights on or off in the screen and not that the backlight power supply from the motherboard is turned on or off.

With the laptop turned on etc, check for voltage (set DMM to 20V DC) on pins 1-3 of the EDP cable. If there's no voltage sometimes the fuse will be located near to the EDP connector (right or left side of the connector). Check if you can follow the traces from pins1-3 to see where they go.

If you can't see any images, then since you have replaced the screen it could be a faulty EDP cable (if there's voltage on the EDP cable) or if there's no voltage and you found the fuse and it is OK then it's something else in the backlight power supply circuit on the motherboard which would require the schematics

Was this answer helpful?

Yes No
Score 1

3 Comments:

Hi @jayeff

Thank you very much for checking for schematics. I can imagine it would be hard to find things that manufacturers want to keep under lock and key.

After your advice, I checked pins 1-3 on the connector and I was getting 3.25 V DC when the laptop was on. Just to clarify, I can see the Lenovo logo on the LCD if I hold it in a certain way or use a flashlight, so it is definitely a backlight issue here.

After that I decided to take the ribbon cable out and continuity test the pins and can say they are fine, pins 1-4 are actually bridged on the connector from the PCB but they do go to 4 other pins on the LCD side.

I decided to take the copper shield off the bottom of the board and lone and behold, there’s a fuse labeled VF1. Checking continuity and it seems to be blown.

I’ll take this board back to my workshop tomorrow and see if I can bridge temporarily for testing or try get another 1062 fuse from somewhere and replace it.

Once again, thank you for your assistance here.

by

@saschawestpfahl

Most backlight fuses are 25V or 32V 3A so try to find one with that value in the correct size.

by

Hi @jayeff,

After getting the new fuse and installing it, I have a working backlight on the screen. I did have to use the 2nd screen unfortunately but the laptop works perfectly. Including touch screen.

Thank you for your assistance with this and hopefully this thread helps others out there too.

by

Add a comment

Add your answer

Sascha Westpfahl will be eternally grateful.
View Statistics:

Past 24 Hours: 3

Past 7 Days: 10

Past 30 Days: 54

All Time: 54