Lenovo Legion 5 won't turn on after display replacement  - Page 1
Forum section: electronics / repair

author: adauphin
author_rank: Unknown
timestamp: February 06, 2025, 06:24:08 am
content: Well, safe bet this was my own stupidity as I know better, but I replaced the display with a genuine Lenovo unit, and I didn't unplug the battery beforehand. Anytime I open the case, I unplug the battery, even to clean it. I guess since I wasn't opening the case, I thought I was safe...that was dumb and I'm upset at myself.That being said, has anyone dealt with one of these? I would think if a display fuse the keyboard would light up, but...no power, no keyboard lights, or amber charging LED when plugged in.Hopefully this is something easy...all input appreciated.

author: adauphin
author_rank: Unknown
timestamp: February 12, 2025, 08:33:21 am
content: I was able to remove the motherboard today, still waiting on a reply for a schematic, but at the power input, I have what I believe is a diode and possibly a fuse? Is the component labeled "85A" a fuse, possibly 8.5A or something else?Either way, no continuity across either, and I'm also reading .7558 K ohms across both components.

author: khaahk
author_rank: Contributor
timestamp: February 12, 2025, 10:00:02 pm
content: 85A is a resistor 750 ohmsFor schematic google for the mainboard code, might be compal nm-d562 or similar.Most commonly the sio controller dies or if unlucky cpu might also be dead.

author: adauphin
author_rank: Unknown
timestamp: February 13, 2025, 10:56:23 am
content: Quote from: khaahk on February 12, 2025, 10:00:02 pmWell...,lol..chalk that one up for me being overly tired. I completely spaced on the fact I was reading "K ohms" and 3 decimal places..Copy that, thanks..I'll try to source another schematic, first place hasn't responded.

author: adauphin
author_rank: Unknown
timestamp: February 14, 2025, 12:50:43 am
content: I started to probe some mosfets and these 4 here above the M.2 slot are where I found some possible issues. As shown on the board in their locations, these are the values between the source and drainPQ 2702 108 ohms PQ2001 .8M ohmsPQ 2701 .8M ohms PQ2003 shortedAs a beginner, I'm not well versed in troubleshooting without a schematic, but figured I would start with the mosfets, I assume 2003 is bad and 2702 is not far off?

author: khaahk
author_rank: Contributor
timestamp: February 14, 2025, 07:36:14 am
content: The mosfets are probably ok but you have a short on 3V rail. You can confirm it by lifting the PL2001 and measuring on which side the short is. Schematic can be found by googling "nm-c911 schematic".Now you have to find the short, the methods are probably well described and depend on equipment at hand. There are a lot of things on that rail.The PQ2702 should be fine, it is 1.2V output and this should be normal resistance for it.

author: adauphin
author_rank: Unknown
timestamp: February 14, 2025, 02:05:26 pm
content: Could I introduce a 3V signal and look for hear with a Flir, before removing the mosfet?I will dig up the schematic and do some homework.

author: khaahk
author_rank: Contributor
timestamp: February 14, 2025, 03:00:13 pm
content: Current will take the least resistance path so no need to remove the mosfet.

author: adauphin
author_rank: Unknown
timestamp: February 19, 2025, 07:52:23 am
content: Quote from: khaahk on February 14, 2025, 07:36:14 amI did find it, thanks. About 80 pages worth of good info. Going to look into it and learn a little as I go. I do enjoy troubleshooting from a diagnostic perspective, been doing that for decades with vehicles but circuit boards are new to me in that regard. I wish I took courses years ago but now trying to bridge that gap now from years of hands on without the basics to come up with the more methodical methods of diagnosing a circuit. It's definitely fun and intriguing.That brings me to a small sidestep and I want to do a separate thread but here's my thoughts..with regards to many videos on circuits and people trying to explain them. It seems (to me at least) that the very basics are left out and that keeps us (rookies) trailing behind a little. Each component plays a part and describing what the components do and how they interact with other components in each device, helps paint a picture on their function and limitations.Way off track but topic for another discussion.

author: adauphin
author_rank: Unknown
timestamp: March 03, 2025, 12:46:24 pm
content: Well, little bit of an update and I wish I had slightly better news, as I may have goofed something up....we shall seeI read through the schematic and to be honest, it's a learning curve and I enjoy that but many aspects I don't understand. I found some 3V circuits but couldn't really find them on the board. I decided to use my DC PSU to apply 3V @300mA, then 5V, then 12V@500mA to the motherboard alone and I could not see any heat through the FLIR.So I reinstalled the motherboard minus the heatsink and tried the voltages again, also no heat. I connected the laptop's PSU and without opening the lid, I looked for heat and right away I found some heat under the WiFi card. I checked the card and the card itself was a little warm. I removed the card and there was still heat in this area.This is what's under that areaI wanted to see if I had 20V so at this capacitor I believe, I had 20V on one side, but nothing on the other.Then while using my needle probe I managed to let it move in my grip and it dragged across something and I had a spark. Needless to say I was quite upset. I believe it may have touched this MOSFET but not sure. The probe was on my DMM and somehow it brushed across a 20V circuit so who freaking knows what may be damaged now. I think this side has a mark but maybe not.I looked at it again under the thermal after my goofup and the heat is the same. I should have gone to bed and finished later but water under the bridge. I really don't want to possibly be looking at a $1K paperweight, but have to take it in stride, very bummed ATM.

author: khaahk
author_rank: Contributor
timestamp: March 08, 2025, 05:37:37 pm
content: PU2001 is heating up because there is too much current drawn from its ldo ouput (pin3), if you measure resistance at PJ2001 you should have low resistance.Solder a thick wire to PJ2001, insert less than 1V and start at 1A, see if something heats up, if not increase the amps until something does show up.

author: u666sa
author_rank: Frequent Contributor
timestamp: March 08, 2025, 06:08:08 pm
content: Anything is possible here, up to GPU (or CPU) dead. To diagnose this mess you need thermal camera.Anything else is not efficient.

author: adauphin
author_rank: Unknown
timestamp: March 09, 2025, 10:22:30 am
content: I started at 1V 500mA, nothing, then 1A, then 1.5A and it hovered around 100mA current draw. I didn't see any heat until I reached around 2.8V, still at 100mA draw. The heat was localized on the PU2001.I probed pin 3 here and have 5K ohms. Both pin 2 & 3 read the same.

author: khaahk
author_rank: Contributor
timestamp: March 09, 2025, 01:12:12 pm
content: Then go to PJ2004, same ammo.

author: adauphin
author_rank: Unknown
timestamp: August 12, 2025, 07:39:57 pm
content: With so much on my plate right now I have not been able to return to the laptop but will try again soon. I appreciate the help so far, might have to source an outside repair but will exhaust my possibilities first.

author: adauphin
author_rank: Unknown
timestamp: October 06, 2025, 09:42:21 pm
content: Quote from: khaahk on March 09, 2025, 01:12:12 pmThank you for your help, during my rookie diagnosing on this motherboard, I accidently touched something I shouldn't have and ended up with a spark.So that leads to my follow up.Quote from: u666sa on March 08, 2025, 06:08:08 pmAfter I had a case of the oopsies, I had a spark and now the CPU is definitely toast.I had someone check it out and confirmed that.So moving forward I found an Ebay seller who has this exact MB from a new system that was parted out, I installed the MB, had it back together and it fired up but I didn't have anything on the display, as well as no HDMI output. This went on for about 30 min doing resets and trying different hard drives since it was the same BIOS on a different MB so I thought that was the issue...until I could barely see the display cable not connected. I think I was trying to fit the MB in with the almost no slack of the cable and it slipped out and I didn't see it as it was tucked under the MB.So I very carefully removed the heatsink, attached the cable,had it back up and running and after about 5 seconds it shut off. I turned it on again and the light blinked and went out, also the charging light is now not lit.Now I want to assume the initial cause for the no power was the new lenovo display or maybe a short in the cable? However the old display was working with a lot of vertical rainbow lines around the damaged area. I have not done anything more to it as now it may just be a surface mount component and still fixable..very frustrating now.