LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

[lctrbrt]

Hello,

I've mentioned computer sitting on my desk and driving me nuts


This device came in for screen replacement and I did it like always;

disconnect battery, replaced the screen, device won't power up anymore

No Power/Charging indicator LED is glowing, no fan spin and no other sign of life.

+5VALW is working but +3VALW has a short to ground which sits between the PJ401 and PJ601. Also PU401 is getting quite hot but I think the fault lies in another part.

I assume that the ENE KB9012 or the CPU has some damage but they look fine and I don't know how to proof my assumption so if any one is here who can help I would be pleased
Also I wouldn't reject a Boardview file for this device but as far as I know this isn't available.

Thanks in advance and stay healthy 😷😬

Schematics: LA-A921P Schematic

[piernov]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

PU401 will heat up if it's trying to supply too much current due to a short to ground on +3VALW (or +3VL). If you disconnect PJ401 PU401 should not heat up anymore as it's been isolated from the short to ground. After disconnecting PJ401 you can also confirm the short is indeed on +3VALW and not +3VALWP.

In any case fastest way to isolate the problem is to inject 3V into +3VALW and check if PCH die (small die on CPU package) is heating up, or the EC.

[lctrbrt]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

Hi Piernov,

thanks for your fast answer.

The funny part is that PU401 is heating up even if PJ401 is disconnected. It's not super hot and touchable. I pulled the PU401 and tested some puns like LX which goes to +3VALWP and then over PJ401 to +3VALW and there is no short. Only if I connect the PJ401.

I'll try this injecting method. Thank you very much.

[mek007]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

i think thats a cpu issues ...just encountered the issue exactly as you described

[ktmmotocross]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

Hi Piernov,

thanks for your fast answer.

The funny part is that PU401 is heating up even if PJ401 is disconnected. It's not super hot and touchable. I pulled the PU401 and tested some puns like LX which goes to +3VALWP and then over PJ401 to +3VALW and there is no short. Only if I connect the PJ401.

I'll try this injecting method. Thank you very much.

\
resistance on +3VLP ?

[krazykipa]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

In any case fastest way to isolate the problem is to inject 3V into +3VALW and check if PCH die (small die on CPU package) is heating up, or the EC.

Thanks for this, I had the same issue on an LA-A342P board. Unfortunately, the PCH heats up and the board is now scrap

[masoodahmad124]

Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

12v mosfet burn and solution with drill pcb