Thinkpads Forum

Hi, I'm trying to repair a thinkpad T420 with no power. Now, after disassembling it and pocking arround, I managed to find this out:

The VCC3M and VCC5M rails are present, but only temporarily, for like 2 sec, and then they die. Same goes for the M1_ON (and VCC5M_ON / VCC3M_ON) singal. VCC3SW is always on.
However, the 5M_PWRG and 3M_PWRG signal are always LOW (0V). My assumption, as someone who is trying to fix a laptop for the first time is that the DC/DC converter regulator chip is kaput.

I'm here asking for advice to see if I might be missing somethinkg.

Posting image of the power circuit.



Full Image: https://i.ibb.co/BNWKWsR/020221-181726.png

i am curious where you found that schematic..?

BillMorrow wrote: ↑

Tue Feb 02, 2021 1:38 pm

i am curious where you found that schematic..?

Free off of Google. It was easy enough. Had to pay for the boardview though.

I would like to add to this that I DO NOT plan to further distribute the data or documentation I may use to fix the issue.
If at any point Lenovo feels I may have surpassed the point doing something in good will for searching out this info whilst trying to fix a product of theirs I like, ask and the data will be removed from this thread.
This is also the only thread I'll open for this issue.

"Might sound dumb having to say this, but there is a reason I'm trying to fix it on my own, and a lawsuit would be the last thing I want with the current situation the world is in."