Lenovo L13 gen3 (2023)

[double_DD]

Hi guys

I have received this laptop to try and repair it (and to learn more in the process).

It was liquid damaged, I found some corrosion near the screen cable that I cleaned. Now I'm left with a short on main power rail (19V).

I was hoping that it would be something simple as a shorted cap around a liquid damaged area, but no.

My problem is, I cannot identify what is shorted. I've inserted 0.9V (to be on the safe side) on mail power rail, and the voltage drops to 0.4V with the max current drawn allowed of 4.8A.
However, the board is cold as ice, I cannot see anything heating up! I don't have a thermal camera (and was hoping not to have to buy one) so I'm spraying board with IPA (not beer ) to see where it evaporates. I've tried on both sides but I can't see absolutely any warm or hot spots.

Also, this is a bit strange laptop, at least to me, as I don't see any mosfets for other power rails (5V, 3.3V, Vcore...), just coils. And from my tests there are no shorts on the any of coils output, just on 19V rail.

I'm a bit scared to try to insert 19V on the rail in case I've missed something, don't want to fry CPU or RAM or whatever, but I need to change something because this approach is not producing results.

Do you think I should up the inserted voltage (and limit max current to 2A or more?), or do you have some other suggestion?

Thanks in advance!


P.S. I was able to find schematic from L13 gen2 on this site which confirmed my initial thoughts and allowed me to check all the power rails.

P.P.S. This is the second laptop that I've torn apart recently, all my "knowledge" comes from watching various youtube channels ))

[double_DD]

Board number is LFR-1 intel 213037-1N, if some other info is needed please let me know. Thanks!

[double_DD]

Green areas are caps that are short to ground (0ohm resistance), purple are resistance coils to ground (bottom right coil is currently missing, removed to isolate input from output, so values are on each side). I haven't seen any coils or shorts on the other side, just some chips (Realtek, ThinkShield...) and connectors

[double_DD]

Hello everyone,

Let me try to revive this post, maybe I could get some help this time.

The story is:
I have this Lenovo L13 gen3 213037-1N laptop, water damaged, no schematic, and I've identified a short on a main power rail. Spent silly $$ to buy thermal camera.
However, I cannot find what is shorted. I've tried inserting voltage on various points on main rail, but NOTHING GETS FREAKING HOT. I've inserted from 0.9 to 19V, board always uses only 0.45-0.5 V with max current allowed. So something is taking 5A without getting hot! There are several "combined MPPX" mosfets that I've tried removing from the board, as I'm not sure how to test them, but the short persists.
Other voltage supplies are not shorted. Previous picture shows shorted caps (on main rail) and measured resistance on various coils.

I've hit a dead end and have no idea what or how to test next.

Any help -advice, idea, schematic...- would be highly appreciated! (And to repeat myself, my knowledge is quite limited)

THX

[mon2]

(Saw the earlier updates - have an older version in my database)

Post clear pics of the power adapter connector area. Nearby will be the DCin mosfets and the charger IC. Need to know the details of each.

[double_DD]

Hi mon2 , thanks for the reply!

I do believe it is L13 from Yoga series (it's not mine, I got it to try and repair it).

I don't understand this image that you've sent, but 2 posts up is a picture of my motherboard. As you can see, heatsink and everything else has been stripped of, it's a bare motherboard, and with thermal camera I cannot find absolutely anything getting even a bit warmer when 5A is applied. I do not think that CPU is shorted because a) resistances at picture above I think are normal and b) even with CPU mosfets removed from the board, so CPU isolated, current consumption is still 5A.

I honestly have no idea how that's even possible.

EDIT:
These are the pictures of input circuit; wire is main rail where I inserted voltage:

[mon2]

At 5A, someone will be heating up. Just a matter of using the thermal camera to locate the part in heat. This part could be on the bottom side of the PCB.

I've inserted 0.9V (to be on the safe side) on mail power rail, and the voltage drops to 0.4V with the max current drawn allowed of 4.8A.

The first course of action would be to hunt down the part that is heating up and hope it is a shorted cap which is causing that local power rail to turn off due to an excessive current draw.

Are you using the official power adapter on this board? Assuming yes, attach this power adapter and review the nearby DCin mosfets that enable / disable to power up the board. We need to review if the power path is ok to create the main power rail.

What is the voltage to ground of this power adapter while it is connected to the board? Measure close to the DCin power connector.

Remove all power -> meter in resistance mode. Place one meter probe onto the main power rail and other OTHER meter probe onto any of the inductors (usually grey in color). Note the resistance. Is the resistance low or high?

If the resistance is LOW, then there could be a serious fault of the high side mosfet leaking the high main power rail onto this lower voltage rail. That is, each inductor is creating a sub-lower voltage rail. For example, 19v input to say 3v3; 19v input to 5v, etc. To create the lower rail, 2 mosfets will pulse ON / OFF to 'dial up' the target lower value. These are called buck regulators. There will be a high side mosfet that takes in the high voltage of 19v and a low side mosfet to shunt the high voltage to ground. This on / off action by the 2 mosfets creates the desired lower voltage rail.

If the high side mosfet leaks which can occur, then there is no more protection and the high voltage floodgate of the mosfet is lost and the low voltage components get killed.

At the output of this lower power rail is an inductor. It is that inductor you are measuring. By checking the resistance path from the main (19v) to the inductor, you are checking if the high side mosfet is leaky or not.

Post the measurements that are considered to be a suspect. Note that this is a different measurement than checking the resistance of the inductor to ground. Check the main power rail to each and every inductor on the board -> hunting / confirming if there is a high side mosfet leakage.

[double_DD]

Thank you for a detailed process of examination and explanation.

Since this particular laptop was received as "liquid damage", my testing path was a bit different. For start, I never connected motherboard to power supply. I opened it, noticed some corrosion -on the first picture in last post, where a wire is soldered and some messy caps, corrosion was present all around those messy caps, then up around the fuse and on the connector on the upper part (this is screen connector). I took those caps out, cleaned everything with IPA, and put still good caps back. That's why they're so messy.
Then I checked with multimeter against the ground, and noticed a 0ohm short. I checked around all coils, and short seems to be present on the input side only, meaning before "combined" mosfets. This indicated to me that all mosfets are most likely OK, but I might be wrong.

On the picture in the much earlier post there is a motherboard with measured resistances between ground and various coils. Since it's 0ohm between main power rail and ground, measurements should be exactly the same.

At that time I didn't have thermal camera, so I opted to insert 0.9V at the soldered wire -which i identified to be main power rail-, and tried to find shorted component by spraying motherboard -both sides- with IPA. I started with 1A and upped to 5A, no conclusive result.
Then I tried cooling the board with the cold spray and checking which part would melt first -on both sides of motherboard- , also with inconclusive results; nothing seemed to get hot even with 5A.

Recently I bought thermal camera, UNI-T UTi721M, and checked the motherboard again, again on both sides. Even after 5-6min running on 5A, NOTHING SEEMS TO GET EVEN A BIT HOTTER. Only warmer patches (that I can find) are around where the + and - probes touch the board.
I know something should get hot, I understand how much of a current 5A is.

At this point I really have no idea how to proceed. I'm even not sure if my original conclusions are valid, since I cannot experimentally prove them.

[piernov]

I'd suggest using real leaded solder, flux and a good soldering iron with appropriate tip. This soldering is not great, and maybe there is a solder bridge somewhere between the power rail and ground. Additionally, when the end cap of SMDs is too corroded, they should be replaced.
Also, is the capacitor next to the polyfuse F5501 really supposed to be there?

[double_DD]

This is exactly what I was thinking lately, that maybe my bad soldering created another short around those caps. This is the first thing I will check next.

I removed the bad caps, and put back only the good looking ones. There's also a chance that I've damaged them when putting them back badly.

Regarding the cap next to the fuse, I will definitely check it closely. Thanks!

[piernov]

Circled in red are capacitors with their end caps damaged. The left one may not even have taken solder.
Circled in yellow is a capacitor with a partially damaged end cap. There is still enough material left for it to be soldered properly, but it is better replaced anyway.

[double_DD]

Well colour me stupid! I've removed those messy caps and the short is mysteriously gone. Apparently I've been chasing my own tail for the last month or so. No wonder I couldn't find anything with thermal camera. 😠
And I've replaced all of them with brand new ones.

The weird part is, I'm almost 100% sure that when I originally removed those caps, short was still present. So either I'm remembering wrong, or removing and putting back other components somehow disappeared the short. Or some of the mosfets I've put back are not properly soldered on.

Anyhow, now checking with my multimeter all coils show high resistance to main rail, and connecting power supply to either of usb-c ports gives me a stabile input 20V. Now I need to reassemble and check if there are some other errors.

Thanks mon2 & piernov for now, I'll be back with updates!

[double_DD]

Update:

Initially, the short was gone and I was able to connect the battery to the board and to charge it.
However, once I connected everything to the board and half assembled the laptop, then one of the CPU combined mosfets decided to die, so now I have again short on the main rail.

Now I just need to find and buy MPPX 8694 (not exactly sure what the last 2 letters are, as they differ on various AliExpress sellers).

Another interesting thing that maybe someone can explain it's functionality:
This laptop has a "battery reset button" in one corner of the board, and I think, but am not 100% sure, that the charging of the battery didn't start until I pressed it (input current was low, 200-300mA, and when I pressed it immediately jumped to almost 3A - maybe it was a pre-charge current and just a coincidence that I pressed at the exact time it went to full charging?)
I never saw it in any repair video, and was only aware of it as I had gone through the schematic (for the L13 gen2).