Black screen Lenovo legion 5 pro 16ACH6H gaming laptop

[VcemPzd]

Hello everyone !

My name is Chris, I am a 30 years old embedded software developer working in the automotive industry. I am really passionate about learning new skills and repairing/crafting stuff. I came around this forum last week with the goal of repairing my faulty gaming laptop, indeed, I was video editing on it when suddenly a black screen popped and never disappeared I bought some stuff to try to repair it and learn as many things as possible about computer repairs but nothing worked so far. When the black screen appeared, my legion 5 pro was connected to my external monitor via HDMI and both went black at the same time while the computer was still on. I powered it off and tried several times to hold the power button for more than 60s with the charger unplugged, tried to disconnect the CMOS battery and hold the power button for 60s... Nothing worked when I powered the computer except once where my login windows appeared but I took too much time to enter the credentials and the screen froze. The second time I was able to get a display, as soon as I entered my credentials and pressed enter, the screen froze again. Since then, I was never able to get a display.

What I decided next is to watch several repair videos on the internet and following what I saw, measured the resistors and voltages that I could without much knowledge on computer repair. I tried to unplug all peripherals that I could (RAM, SSDs, battery) but same result, no display, just my RGB keyboard glowing and a black screen. Numlock and MAJ always off so from my understanding the computer never left POST. After removing the heatsink, I verified the temperature of both the CPU and GPU, both heat up as soon as I plug the charger (battery disconnected) which means that the current/voltages should be correct. I checked the voltages I got across all 5 GPU inductances and it was at 0,75V.

Next, I ordered a CH341A programmer and a hot air / soldering station to try to reprogram the BIOS. With the 1.8V adapter, I tried to read the BIOS chip with the clip with no success, I then unsoldered carefully the chip using flux and hot air, soldered it on a small board that was included in my kit and was able to read its content on the computer using AS Programmer. I saved my dump BIOS, copied the DMI section of it and copied it to a BIOS I extracted from lenovo website (GKCN65WW). I then erased the chip and programmed it.

I then soldered back the chip to the motherboard and same behavior, the computer powers itself up, CPU and GPU heat up, keyboard lights up, Numlock and MAJ stay off and still no picture. I don't know what else could I check/try to make it work again :S
The computer was always perfectly taken care of, never got dropped, no liquid ever got close to it. I didn't see any fried signs on the motherboard so I cannot explain what happened there. I had it since February 2022 so it is not under warranty anymore...

The other route I thought of is the EC chip but I am not sure I want to dive into that route without external advices. I saw that I need a programmer like the SVOD programmer to program it but not really down to invest in it. I tried to read the pins on the EC chip but they are that tiny that I feel like it's a dead end given that don't even have a datasheet of it. I checked pin number 1 voltage and it was 0v, pin number 2 and few other were at 3.3V.

After that I mounted the laptop back since I am now kinda lost...

Does anybody can help / advise me please ? Anyone experienced the same behavior with his laptop ?

Best regards,

Chris

[reformatt]

In my experience, this very much sounds like bad balls under the CPU. Pretty common fault these days and I attribute it to the board being twisted/flexed when you open and close the lid from either side, rather than the middle. Only cure is to reball the CPU or replace the board. Forget reballing CPU's on Lenovo boards, even if you have the right gear to do it. They use a black glue which makes removal of the chip very difficult without damaging the pads on the PCB. Other vendors use soft glue material that comes off pretty easy with heat, so I'm not sure what Lenovo is trying to achieve with this stuff, other than to prevent anyone from reworking their boards.

General approach for me is to check the RAM first. If it has dual slots, try one known good RAM in each one alternately. I also check the RAM slot pins for contamination, or loose pins to the PCB. Then check for presence of CPU Vcore power rails. If present, then check current consumption from external power supply (without battery) to see if the current is static or varying.

I rule out BIOS/EC etc as the laptop does boot, but freezes. If either of those things were at play, you wouldn't get to that point.

[VcemPzd]

In my experience, this very much sounds like bad balls under the CPU. Pretty common fault these days and I attribute it to the board being twisted/flexed when you open and close the lid from either side, rather than the middle. Only cure is to reball the CPU or replace the board. Forget reballing CPU's on Lenovo boards, even if you have the right gear to do it. They use a black glue which makes removal of the chip very difficult without damaging the pads on the PCB. Other vendors use soft glue material that comes off pretty easy with heat, so I'm not sure what Lenovo is trying to achieve with this stuff, other than to prevent anyone from reworking their boards.

General approach for me is to check the RAM first. If it has dual slots, try one known good RAM in each one alternately. I also check the RAM slot pins for contamination, or loose pins to the PCB. Then check for presence of CPU Vcore power rails. If present, then check current consumption from external power supply (without battery) to see if the current is static or varying.

I rule out BIOS/EC etc as the laptop does boot, but freezes. If either of those things were at play, you wouldn't get to that point.

Hi man, first of all, thanks for your answer ! The problem occurred during video editing so I am not really sure that it is linked to the way I open the lid, or am I wrong ? So if it is the CPU , reballing is a dead end right ? How to check exactly if CPU is working fine given the voltages I can measure around ? Do you have a link or something explaining it please ? Also, do you have schematics for this board and especially the neighborhood of the CPU ? (I have an NM-D562 Rev 2.0 MB) My CPU heats up when the computer starts, same as GPU. I don't have any display anymore so I don't even experience the freezing I had anymore... I tried to start it with/without RAM but same result.

What does checking for loose pins exactly means ? How to chehck the CPU Vcore power rail please but yeah, the laptop doesn't boot anymore and stops after few seconds : keyboard lights up, fans start spinning real quick but stop, the power button lights up too but then everything stops after maybe 30 seconds. Display stays black, there's not even back light present...

[reformatt]

You can use the Rev 1 schematics, they are here on this forum if you do a search. Vcore rails would be those on pg 95 of the schematic. Measure at the coils PL1005, PL1006 etc. Should be around 1V or so. The presence of these indicate that all your other rails are ok, since CPU power is only enabled once all the preceding ones in the sequence are good. You won't get a display unless the CPU successfully POST's. Only takes one broken ball under the CPU for a signal to be missing, and the sequence stops. There is no link I can give you, as this is based on my experience on fault finding over many years.

That said, I usually pull these boards out first and do an examination under the microscope looking for any spots that may be corroded. Lenovo boards tend to be well protected though with black plastic on the keyboard facing side. Corrosion spots can be very small, as it's often due to an insect dying/crapping on the board. As for the RAM slots, I look at the pins at either end of the connector(s) and make sure they are firmly soldered to the board.

Then I look at input current from DC power supply without battery, as this will often tell you a bit about what is going on. Try it with RAM and without. A static current usually means there is no CPU activity. A CPU that is actively POST'ing will have the current varying up and down for example. It's just something you learn based on experience.

So if the board is clean, the RAM slots are fine, CPU volts are ok, it's often bad balls or bad CPU. I don't spend too much time on it. Given the motherboards are so expensive for gaming systems, they aren't economical to repair, and you move on to the next job.

[VcemPzd]

You can use the Rev 1 schematics, they are here on this forum if you do a search. Vcore rails would be those on pg 95 of the schematic. Measure at the coils PL1005, PL1006 etc. Should be around 1V or so. The presence of these indicate that all your other rails are ok, since CPU power is only enabled once all the preceding ones in the sequence are good. You won't get a display unless the CPU successfully POST's. Only takes one broken ball under the CPU for a signal to be missing, and the sequence stops. There is no link I can give you, as this is based on my experience on fault finding over many years.

That said, I usually pull these boards out first and do an examination under the microscope looking for any spots that may be corroded. Lenovo boards tend to be well protected though with black plastic on the keyboard facing side. Corrosion spots can be very small, as it's often due to an insect dying/crapping on the board. As for the RAM slots, I look at the pins at either end of the connector(s) and make sure they are firmly soldered to the board.

Then I look at input current from DC power supply without battery, as this will often tell you a bit about what is going on. Try it with RAM and without. A static current usually means there is no CPU activity. A CPU that is actively POST'ing will have the current varying up and down for example. It's just something you learn based on experience.

So if the board is clean, the RAM slots are fine, CPU volts are ok, it's often bad balls or bad CPU. I don't spend too much time on it. Given the motherboards are so expensive for gaming systems, they aren't economical to repair, and you move on to the next job.

Thanks man, I'll check all that when I get back home and if it gets me nowhere, I'll leave it and buy a new laptop when I found one (with a warranty extension this time given the price of the laptop :S)

Also, is there something I can check near GPU ? In terms of voltages or resistor values ?
What about the LCD screen ? Though I don't think that a faulty screen would prevent POSTing or an external display from showing images...

It's really bad the way laptops are made, all soldered, one broken thing and good to be thrown away 🤬