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01-01-2014

tes

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thinkpad t400 AC Adapter acceptable voltage

2014-01-01, 15:28 PM

I bought an used thinkpad t400 and it's working fine. But when I measure the output voltage from the AC adapter, I get 20.7 - 20.8V. Is this ok? It should be 20V. I checked the manual and it says:

 

"If the voltage is not correct, replace the AC adapter.
4. If the voltage is acceptable, do the following:
v Replace the system board.
v If the problem persists, go to “FRU tests” on page 50."

 

What does "acceptable" or "not correct" mean? Is it safe to have 0.7 or 0.8V above what is normal? I wonder why they didn't write a specific value in V for when to change the AC adapter.

 

What can go wrong if I continue to use this charger? Can I fix it so I can get 20V output?

 

 

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8975 Posts

01-13-2008

United States of America

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Re: thinkpad t400 AC Adapter acceptable voltage

2014-01-01, 15:39 PM

Hello and welcome,

 

I just measured the power bricks on the T61 and T420.  Both came in at 20.6V.

 

I don't know if Lenovo publishes an official tolerance,  but in my line of work power bricks and wall-warts have a 5% or even 10% tolerance.

 

Are you measuring with the brick disconnected from the laptop?  I don't know how tightly regulated these little power supplies are.  The voltage may well sag to 20V - or less - when there's a load on.

 

Long way of saying that I think you're probably just fine.

 

Z.


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The fine print: I do not work for, nor do I speak for Lenovo. Unsolicited private messages will be ignored - questions and answers belong in the forum so that others may contribute and benefit. ... GeezBlog

 

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3 Posts

01-01-2014

tes

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Re: thinkpad t400 AC Adapter acceptable voltage

2014-01-01, 16:01 PM

Hello, thank you for your reply.

 

Yes, I measured the brick(I guess you mean the adapter) with the laptop  disconnected.

 

I also checked other adapters from different laptop brands and they were 0.1-0.2V above normal specs. But from your measurements it seems that this it's normal for thinkpad bricks. But still, it would be nice from Lenovo to be more specific in the manual above the adapter tolerance instead of using vague terms like: "not correct" or "acceptable" Voltage.

 

If others are interested in this, please post your measurements.

 

 

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