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The slimmer version of the bulkier ThinkPad T420. The T420s is notable for its lower battery life and noisier fan compared to the original T420 laptop.

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T420 will not power on

I have tried plugging it and booting without the battery and trying a different t420's keyboard to no avail. the light on the keyboard doesn't light up and the computer itself doesnt make any of the normal fan sounds when you try to power it.

any thing els i could try?

Thanks, Spoofo9t9

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I have a similar problem, in that the laptop just stopped working. No lights, nothing when its plugged in. I tried all the easy stuff. I'm now trying to see if its the powerjack module or what component on the MB went bad. Ambitious I know. Any advice on trying to narrow down problem would be helpful. A schematic and boardview would be lovely. Thanks.


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Hi @msh1919 ,

No schematic but perhaps the service manual will be of some help or at least a start.

On p.106 it details the necessary pre-requisite steps and then the procedure to remove the DC-In jack.

You could start from this point. With the power and battery totally removed from the laptop, use an Ohmmeter to measure that the jack itself is OK

Here is the part number for the DC-In jack, in case it is faulty and you have to order a new one, 04W1635 (found on p.140)

Just search online using the number only to get results for suppliers of the part.

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also google for CMOS (try to hold the power button for a minute and then press it again), if you didnt setup your laptop to turn up after attaching an AC, then to try to replace the keyboard might help. never ignore the beeps.

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Spoofo9t9 will be eternally grateful.
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