Thinkpad L480 , Short To Ground, CPU gets Hot

[juergenb]

Hi,

i would like to hear your thoughts.
This is my first attempt to repair a broken ThinkPad.

I got a Thinkpad L480 with no power or any sign of life.
I checked Memory Module, WiFi Module and Display, all are fine.

I have Schematics and Board View.

The L480 has no LED and the fan is not spinning or moving with the USB-C PSU (65W).

I measured all Coils and all i have is

+5VALW with 5V
+3VALW with 0V

I opened PJ202 and i get +3V at +3VALW.

So i checked for any shorted CAP (didn´t find any).

I injected 1V / 5A at PJ202 but nothing got hot.
I used Ice Spray over the whole Board, nothing gets hot.

After removing the Heatsink, the only thing that was hot was the i5-8530U smaller Die.

If i thouch the Die with my Lips, i get a tiny electric Shock ...

So i assume, the CPU i shorted.

Is there anything else i can try or is this Board now a donor Board for Parts?

Thanks

Jürgen

[piernov]

Re: Thinkpad L480 , Short To Ground, CPU gets Hot

Obviously PCH is shorted as always.

[coltron]

Re: Thinkpad L480 , Short To Ground, CPU gets Hot

I have an hp 250 g5 with a similar 3v short issue. The PCH die next to the cpu gets warm, when I cleaned the grease off, using my magnifying glass I could see a small gritty looking crator in the mirror finish of the chip.
There are capacitors underneath the chip on the other side of the board, and undeterred removed every shorted cap i could find, but the caps i removed all tested good.
Freezer spray would of been a quicker diagnostic tool, every days a school day.

[mcplslg123]

Re: Thinkpad L480 , Short To Ground, CPU gets Hot

No point removing those tiny capacitor on back of SOC unless and otherwise its liquid spilled/RTC shorted issue.

[reformatt]

Re: Thinkpad L480 , Short To Ground, CPU gets Hot

Although initially expensive, a thermal camera will save you countless hours of time. Can't put a price on that.