Lenovo Yoga 460 / LCL-1 / 14283 -2 short

[Pferd5]

Hi.

I am kind of a noob but I try (hard) to learn fixing Lenovo Notebooks.
Currently I'm working on Yoga 460 (LCL-1 / 14283 -2).
The first problem that I see is that 3.3v ist kind of shorted to ground.
Unfortunatly I haven't found any Schematic to this board (or similar)

kind of shorted to ground because:
the big (I/O Chip) gets 3.3v (and other points on the board) but the Bios Chip is shorted to ground and the biggest Problem is: I can't find the damn 3.3v PowerRail.

I messured every coil at least 10 times. All coils (except 1) are 0.00v.
Should there be a coil with 3.3v?

0.222v, idle consumption is 19v / 0.023amps.

It's not very important to fix this board it's more for education purpose.

Can anyone someone help me / guide me to troubleshoot? Next I wanted to apply 3.3v with external power supply to find the short (hot component) but as I can't find the powerrail I don't know where I should apply the voltage.

I also tried to search the board randomly in diode mode to find a link from working 3.3v to some power supply ...but with no success. weird.

[mcplslg123]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

Its easy to find 3.3v rail my friend. Look for all IC's connected to coils and check there datasheets. Normally these newer boards use silergy IC's with prefix like MS etc.

[MJ-meo-dmt]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

Usually you can see/find the 3.3/5v starting point easy by finding usually two similar coils next or very close to each other. Along with 4 mosfets usually inline (next to each other or 2x2 across) 3rd image bottom right behind those usbs near that grommet.

[Pferd5]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

I messured every mosfet an coil more than once. As long as I recongnize them. I just don't understand why I have 3.3volts on some parts but can't find the source.

I labed some gates in addition. Otherwise they are 0v.

On the other side of the board next to the power connector the mosfet (on the left) has 0.491v input. The (i think it is but could be wrong about) Diode next to the connector PD4410 pulls down the 19v to 0.491 (connects to mosfet).

The coils above the cpu are 0v, also as all coils / mosfets under the ram slot.


I also found some steady 5v point. next to the USB ports.

[SMDFlea]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

Check the QFN IC`s for one marked 5X = ,for the 3.3v 5v source.

https://www.elvikom.pl/lenovo-p40-yo...je-t54075.html

[MJ-meo-dmt]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

I suspect the IC above those 4 mosfets to the right is the 3.3/5V IC.... No way to confirm but that seems the most likely. (I am working off the last image you posted with the voltages black lines and yellow lines...)

Anyways I want to post something here from a Yoga 3 the Chart that shows which rails switch on & when. Only to give you an idea... I have no idea how much you know apart from what you stated in the first post So not being rude or anything like that

See the attached image. This is pretty much the same for most boards, in a few cases some things are a bit different but I'm not going to go into that now. First understand the basics of what to expect and what to look for.

19V (Or what ever the adapter voltage is. And make sure it goes into the board. Which in your case it seems it does.

then 3.3V & 5V ALW (Always on depending on supply type)
In your case it seems like this is the issue you don't have those on the supply rail.

I wouldn't just inject 3.3V or 5V into the rail... You can seriously fuk shit up... Assuming you can even limit the current on that external PSU.

Check your resistances...

EDIT: To add to what SMDFlea said yes look for something like that 5X = xx, or JD EA, Almost like random symbols/letters but I have seen the 5X = something more.
EDIT2: Here is an image of what SMDFlea added of the actual chip. LINK
EDIT3: And here is a possible datasheet for the chip in question.

You could use that datasheet and test around the chip to see what you get, because I found sometimes the chip would be okay and its acting up because of something further down the rail... Something small and stupid sometimes. or even something before the chip, is it even switched on?

[Pferd5]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

Thank you all very much!

So I think you were all guessing right. The small chip with the edge bounding is the 3.3v and 5v power. It's marked with "5x = 2L 26F" How the **** should anybody know what this chip really is? (I guess you know the chip and marking while working with other boards and schematics)

Not sure how to remove this edge bounding stuff?! Anyway..
I was testing and measuring some stuff here an there and also briged some of the first mosfets (for 19v flow) but in the end I ended up with no result.

Maybe I'm stupid at this point but, as said, this board is for educational purpose: I tried to put 3.3v into the power rail right after the IC Output.

I only used 0.1amps... which means no heating at all. I also tried to put 19v als output voltage on some of the mosfets to see what's happening but only weird stuff happend... PSU was set to: 19v and 2,5A.

It's is allways takeing 19v with 0.02A. In some situations it took 0.1v and all the 2.5A. While further testing with the 3.3v (0.2-0.5A max) to inject on random 3.3v locations the max draw was 3.3v with 0.1A.

In the end i decided to set the PSU to 3.3v and 4A and put it into the BIOS-Chip pad to see whats happening. It draw 0.1v and all the 4A.

The only thing that is getting warm is the PCH (from the CPU) - I guess this means this chip is toast?


Currently it's all behaving the same as before.

Currently I'm also thinking more than one thing is shorted, as the area in the red box, also the mosfets drain/source is shorted.

Please let me know what you think. Comment on anything you like, the board, the way I did it, what I did (terribly) wrong... anything.

thanks in advanced.

[mcplslg123]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

5x =rt6575dgqw

[piernov]

Re: Lenovo Yoga 460 / LCL-1 / 14283 -2 short

If injecting voltage on the 3.3V line makes the PCH heat up, then yes it's dead. It should only heat up when injecting on 1.05V core voltage line.