Looking to learn about troubleshooting my Lenovo L14 Gen 1

[eliasseverholt]

Hello!

Unfortunately my Lenovo L14 Gen 1 (motherboard NM-C741) was involved in a terrible mishap. At first, one of my friends accidentally spilled coffee on it which made some of the ports stop working but the computer worked fine otherwise. After that I stupidly opended it and forgot to disconnect the battery... One thing leads to another and I accidentally short it between two components (unfortunately I do not remember which components). After that I get nothing, no charging indication, no boot indication, no fan spin, nothing.

So I'd love to learn my mistakes and learn more about troubleshooting on component level. So far I have identified that the VSYS15 rail correctly supplies 9.2V, however I have also identified that I do not get any VCC5M or VCC3M.
So far I've used this schematic along with a board diagram that I found online which has helped me locate the components.

If anyone would have a step by step process of troubleshooting I would be very keen to know it. Also, in the case of a short between components, what component can I expect to be broken? Is it possible to somewhat predict?

Looking forward for your replies!

[eliasseverholt]

I did some more troubleshooting, the chip PU0501 which is responsible for creating the VCC3M rail gets incredibly hot (I guess a short somewhere). Anyway, I'll continue to troubleshoot

[Lifeisfun]

Hi there, did you manage to find what was the problem? Facing the same issue on E15, same PU0501 chip is getting very hot.
Thanks

[mon2]

Remove all power. No battery either. Meter in resistance mode. Measure the resistance to ground of PL0501 inductor which is the output of the PU0501 switching regulator. The resistance will confirm if there is a shorted part on this rail or not. Post the measurement in ohms. If your meter is not an automatic type, select a higher resistance scale till you have a measurement.

[Lifeisfun]

Remove all power. No battery either. Meter in resistance mode. Measure the resistance to ground of PL0501 inductor which is the output of the PU0501 switching regulator. The resistance will confirm if there is a shorted part on this rail or not. Post the measurement in ohms. If your meter is not an automatic type, select a higher resistance scale till you have a measurement.

Thank you very much for your reply!
I attached schematic in that area with measurements (when I shorten my multimeter leads the meter is showing 0.2ohm)
When power is applied there is 0V on the PL0501 inductor and 0.3V on pin 5 LDO
The other pic is the chip it self with marking of the area where it starts to burn hot.

[Lifeisfun]

I just compared to the 5V power supply chip, and that one even with 0V on the coil still provides 5V on the LDO pin also resistance measured on that coil is in kohm range unlike the 6ohms on the 3V coil.

[Lifeisfun]

I took it step further and injected 2.8V/0,9A to the 3V rail and the PCH gets slightly warm (thermal cam pics) and the 3.3V chip still lights up like a charismas tree in the same corner.

[mon2]

So the ldo rail and all parts camped on this rail are suspects. If you feel comfortable, suggest to isolate the ldo rail by removing the pr0506 short (blue colour in the schematics) on the pcb. Then test which side is shorted. Is it the producer (regulator) side or the downstream (consumer) side that is with a short? The shorted part maybe the filter capacitor on this ldo rail. Do not power up till we learn more about the state of this rail.

[Lifeisfun]

So the ldo rail and all parts camped on this rail are suspects. If you feel comfortable, suggest to isolate the ldo rail by removing the pr0506 short (blue colour in the schematics) on the pcb. Then test which side is shorted. Is it the producer (regulator) side or the downstream (consumer) side that is with a short? The shorted part maybe the filter capacitor on this ldo rail. Do not power up till we learn more about the state of this rail.

Much appreciate your time trying to help!
I'm unfortunately unclear what the pr0506 marking means since it's not marked on the board it self.
Is it the jumper that is connecting board layers I marked on the pic on pin4?
Would heating it up and using solder sucker to remove it work?
Thanks

[m1ch43lzm]

Hi

Would heating it up and using solder sucker to remove it work?

That's a test point, what you suggest won't work in this case
I marked in yellow the "jumper", it's the wide part of trace itself next to the capacitor PC0515

I'd remove the ic in this case to check

[Lifeisfun]

Hi

That's a test point, what you suggest won't work in this case
I marked in yellow the "jumper", it's the wide part of trace itself next to the capacitor PC0515

I'd remove the ic in this case to check

Thank you!

Oh, Ok, I thought it will be some kind of removable jumper
Chip is out, now there is 48ohm resistance on the PL0501 inductor, 48ohm on pin4, but still only 1.9ohm on the LDO pin 5

[Lifeisfun]

Now with the voltage regulator chip removed, is it safe to inject some voltage on the LDO pin 5 to see if there is anything burning?
I did check all capacitors on the board but didn't find any dead shorts, only the 1.9ohm everywhere on the VCC3SW line.

Thanks

[m1ch43lzm]

Lifeisfun Your board model is FE4A0/FE5A0 NM-C421
From schematics found here https://www.badcaps.net/forum/troubl...38#post1555838

VCC3SW goes to the EC IT8227, you can check injecting 1v to confirm

[Lifeisfun]

Sorry to ask over and over but I have very little experience with repair like this, and watching YT will give you only very little details.

When I injected 1V to the VCC3SW it takes about 400mA (my limit was set to 1A) The IT8227 temperature was about 27C and this was the only component on the board that warmed up.
Injecting 1V/1A to the VCC3M it took only 32mA and nothing was getting warm.

Can someone please experienced tell me if this does mean something?

Thank you folks!

[m1ch43lzm]

If it's drawing 400mA, VCC3SW is only supposed to handle up to 100mA

Try 1.5v on VCC3SW, if the current goes higher and EC gets hotter, you need a new one

EC needs to be programmed, you may find sellers on ebay/aliexpress which sell them preprogrammed, you need to give them the board model (NM-C421) and EC model (IT8227E-256)

Related topic about programming IT8227 https://www.badcaps.net/forum/troubl...to-it8227e-256

[Lifeisfun]

If it's drawing 400mA, VCC3SW is only supposed to handle up to 100mA

Try 1.5v on VCC3SW, if the current goes higher and EC gets hotter, you need a new one

EC needs to be programmed, you may find sellers on ebay/aliexpress which sell them preprogrammed, you need to give them the board model (NM-C421) and EC model (IT8227E-256)

Related topic about programming IT8227 https://www.badcaps.net/forum/troubl...to-it8227e-256

Thank you very much for the diagnostic help and possible solution!
I guess it will be best for me to order preprogrammed chip, since I wouldn't use the programmer enough.
Did you ever order from someone who you could recommend?

Thanks

[m1ch43lzm]

Did you ever order from someone who you could recommend?.

Sorry, i can't give you a particular recommendation, I just search on aliexpress and ask the seller before buying
you may ask other laptop repair shops near you that do motherboard repair

[Lifeisfun]

Sorry, i can't give you a particular recommendation, I just search on aliexpress and ask the seller before buying
you may ask other laptop repair shops near you that do motherboard repair

Thank you!

[Lifeisfun]

I have removed the EC chip and now the short is gone, my question is, can I reinstall back the 3.3V voltage regulator and test if it still works or this is not save move? or it will not work without the EC chip installed?
I also learned that I will need to use the Lenovo utility (ThinkPad Config Information Update Utility) to add back the model# and serial number.
This must be done immediately or I can do that anytime after if I get it to boot and work properly?
Any particular version that is best to use? I found several versions and I'm not sure what is the one that should be used to create the USB drive.


Thanks for all the help!

[m1ch43lzm]

You can measure the regulator itself with multimeter if it's not shorted, according to the pinout from post #5
Measure resistance to GND on the regulator itself, also test with diode mode on multimeter (red probe on GND, black probe goes to the other pins), post the readings

I would look for new regulator SYX198BQNC, check the markings on the IC itself (RFxxx), get a pack of 5-10, they're cheap, sometimes you may get faulty ICs from china sellers...

can I reinstall back the 3.3V voltage regulator and test if it still works or this is not save move? or it will not work without the EC chip installed?

If you confirm it's not shorted, you should get back VCC3SW and VCC3M (and corresponding 5v rails if i'm not mistaken), remember that the LDO powers the EC so at least you should get the LDO output

I also learned that I will need to use the Lenovo utility (ThinkPad Config Information Update Utility) to add back the model# and serial number.
This must be done immediately or I can do that anytime after if I get it to boot and work properly?

I don't think you need to edit that info, as it's stored on BIOS chip, unless you flashed a different BIOS with external programmer (and don't have a backup of original BIOS in that case)

Only the EC needs to be programmed, that's why i suggest to buy preprogrammed EC, as the programmers are expensive if you're not doing many repairs to justify the cost
Laptop shouold power on and show image in that case, maybe an error message, i don't know the specific details on that model