Thinkpad t470 short on vcc3m , can't find culprit

[disorder]

hello,

i have a lenovo thinkpad t470 to fix
sudenly no power no start
no liquid damage

i find a short on vcc3m line, desolder the power coil, and the short is not on the side of TPS51285B

when i inject 3v 2amp with my power supply i have a consumption of 0.9 amp (either i up intensity over 2amp) and nothing is hot

can you help me guys ?

thank you

[mon2]

Re: Thinkpad t470 short on vcc3m , can't find culprit

What is the resistance to ground of VCC3M ?

[disorder]

Re: Thinkpad t470 short on vcc3m , can't find culprit

hello

got 3.6ohms

[mon2]

Re: Thinkpad t470 short on vcc3m , can't find culprit

I will suggest to keep the voltage down (3v is ok) and increase the current and look for a bad shorting cap with a thermal camera or IPA poured over the parts.

Search for 'VCC3M' in the schematic and inspect the caps on this same rail.

It appears to also link to the PCH so that may be an idea to review the CPU / PCH (page 16 of the schematic) to see if it is heating up. You will have to remove the heatsink to observe.

Is the display panel attached ? The VCC3M also powers the display.

[disorder]

Re: Thinkpad t470 short on vcc3m , can't find culprit

ok that's weird, got the left side of the CPU getting hot.

so i can put back that board on it's place, RIP little board

[mon2]

Re: Thinkpad t470 short on vcc3m , can't find culprit

yup.



On this note - been playing with our BGA rework machine and it is quite simple to operate (so far). We hope to replace the CPU & memory on some logic boards soon..will update this forum with our results but need to study the effort required. Rewa has some videos on this topic if I recall correctly.

[mcplslg123]

Re: Thinkpad t470 short on vcc3m , can't find culprit

Has succesfully replaced memory and SOC on many boards succesfully but the effort doesnt match the rewards. Getting a new working SOC is almost next to impossible. So need to get an SOC from a scrap board where SOC is known good,get it reballed and then proceed to install on target board. thats too much effort for the charges custome is willing to pay. I do it only on boards which are not freely available and/or are very expensive.