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Old 03-21-2020, 05:51 AM   #1
lctrbrt
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Unhappy LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

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
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Old 03-21-2020, 06:04 AM   #2
piernov
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Default 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.
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Old 03-21-2020, 06:16 AM   #3
lctrbrt
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Default 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.
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Old 06-11-2021, 04:53 AM   #4
mek007
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Default Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

i think thats a cpu issues ...just encountered the issue exactly as you described
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Old 06-11-2021, 09:41 AM   #5
ktmmotocross
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Default Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

Quote:
Originally Posted by lctrbrt View Post
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 ?
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Old 11-18-2021, 02:43 PM   #6
krazykipa
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Default Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

Quote:
Originally Posted by piernov View Post
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
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