Lenovo ThinkPad Edge E420 runs only on battery, detects charger but won't charge or run on AC

lebowitzit

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Dec 30, 2012
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I am trying to fix a Lenovo ThinkPad Edge E420 that won't work with its AC adapter, but detects its presence, as strange as this may sound. Over the last couple of weeks, it acted as if there were a loose connection somewhere: sometimes it was possible to get it to work and charge the battery by moving the cord or the computer around. After awhile, though, it stopped charging altogether.

I have a compatible ThinkPad (SL410), so I used that to test the E420's AC adaper and battery. The E420's battery charges up just fine in my ThinkPad SL410 using either AC adapter. I also used Lenovo's ThinkVantage Power Manager to check the health of his battery, and it still reads as healthy. Meanwhile, I confirmed that the E420 can run on, but not recharge, either battery, no matter whose AC adapter is connected.

When I ran Lenovo ThinkVantage Power Manager on the E420, it detected the presence of an AC adapter when one was connected, and even displayed the amount of current it was receiving from the adapter. I ran Power Manager on the SL410 and compared that readouts on both computers for each adapters, and they were similar.

All of the above would seem to rule out problems with the E420's AC adapter and battery.

One curious symptom I noticed is that the E420's charge indicator light - a tiny LED located next to the power jack - only lights when the AC adapter is connected and a charged battery is installed. If I remove the battery, the computer loses power and the charge indicator light goes off. If I leave the battery in and unplug the AC adapter, the charge light goes off (and, of course, Power Manager reports that there's no longer an AC adapter connected).

The behavior - i.e., runs on battery, but not on adapter, including behavior of the charge indicator light - persists whether or not Windows is running, so it's definitely not a problem with Windows. I did try a BIOS update after I had recharged the E420's battery, but that did not fix the problem.

All of this points to a hardware problem. The question is: where? My first inclination is to try replacing the power/Ethernet board, since that's much less expensive than replacing the motherboard. (Unlike many laptops, the Lenovo ThinkPad Edge E420's power jack - and Ethernet jack - is mounted on a card that is relatively inexpensive to replace compared to the motherboard.) But I would welcome suggestions from people more familiar with the Lenovo ThinkPad Edge E420.

Thanks in advance,

Mark Lebowitz
Chicago, IL
 

lebowitzit

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Dec 30, 2012
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I opened up the laptop and looked at the power/Ethernet board. Curiously, that board had dirt deposits and corrosion consistent with water damage, even though the rest of the computer looked immaculate both inside and out. I replaced the board, and the computer began charging and running normally from the AC adapter.

The only mystery to me is how the power/Ethernet board - which is nestled in a corner of the computer and surrounded by other components - could have gotten damaged by water while nothing else around it showed any sign of so much as a splatter of any kind of liquid. I suspect the answer may have something to do with an in-warranty repair that was done by an authorized Lenovo facility when the computer was just a few months old, but without more information about what was done at the time, I guess this will remain a mystery.

Mark Lebowitz
Chicago, IL
 
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