Strange AC/battery behavior after teardown

[Sweater Fish Deluxe]

Last night I decided to clean out and reapply the thermal paste in my newly purchased T420s. That did successfully lower my max temps by about 10 degrees and fix the sudden temperature spikes I was getting under moderate load (YAY!), but apparently in the process I may have screwed something else up (CRY...)

The computer no longer seems to recognize that the AC adapter is plugged in even though it does get power from it:

1) I get no power control beeps when inserting or removing the AC adapter, Power Manager does not give information about the wattage of the currently inserted adapter (90W or 65W) and it doesn't switch to the AC settings for the power plan.

2) With both the AC and battery in, Power Manager does report that draw from the battery is 0 and the battery does not discharge.

3) In fact, the battery even charges, though it seems to be doing it pretty slowly, maybe 1% every 10 or 15 minutes. The Power Manager tooltip even pops up if I hover over the gauge and gives an apparently accurate estimate to time to full charge, though it ignores my custom charge thresholds and charges all the way to 99 or 100%.

4) With the AC in, I can remove the battery if the laptop is running. The Power Manager gauge now does show the AC plug icon, though the computer still behaves as if it's in battery mode in terms of power plan settings.

5) On battery, without AC, all behavior seems to be normal.

6) With the laptop off, if I remove the battery and try to power on with just AC I get an "019 Critical Low Battery" error after the Thinkpad splash screen and it will not boot (or enter BIOS).


I've searched around and see several posts with similar, but not identical, symptoms. The fact that my battery does charge, though slowly, seems to be unique.

I've tried recommendations from other threads, including:

1) Using a different AC adapter.

2) With the computer off, remove the AC plug, battery, and CMOS battery (and RAM, SDD, and optical drive just for the hell of it) then press power button 10 times, holding it 30 seconds on the last press.

3) On AC and no battery, uninstall the ACPI-compliant battery method from Device Manager and also uninstall Power Manager and the Lenovo PM driver, reboot on battery.

No luck with any of those. Everything is exactly the same.

I believe symptom 6 above means that this is a hardware problem and since solutions 1 and 2 didn't work, I've probably shorted a component in the charging circuit. I used Arctic Ceramique 2 thermal paste, which should be non-conductive, but the old thermal paste looked silver, so might be conductive. I doubt it got it anywhere else on the board, though I may have pushed some out a bit on the CPU under the little plastic cover. Any chance that could cause these symptoms in the charging circuit?

Anything else to try other than testing and replacing the million tiny components on the system board? I don't think I could do that, though maybe if there's one or two larger components I should test, I could give it a try.

[TankPad]

I doubt the problem lies in the thermal paste itself. I reckon it'll be more in relation to the daughter board that the power jack is attached to. Check the connections on it again and maybe re-seat it.
It looks like this.



I had an issue with one of these in the past where a resistor on it was not properly soldered on and actually lifted off the board slightly. but didn't fully detatch so it wasn't obvious as to what the problem was. I might still have it knocking around. I'll take a pic if I can find it.

[Sweater Fish Deluxe]

Okay, I checked that power sub-board, but can't find anything wrong with it visually or the way it's connected. Someday I may try to inspect it electrically or just replace it, but for now I've already gotten used to my laptop's new behavior. I think I was wrong about it taking longer to charge the battery, it only goes slow above 90%, which actually may have always been the case. So really, the only change is that I have to switch power profiles manually when plugging/unplugging the AC. Not a super big deal.

Does anyone have any ideas for how to automate detection of this, though? I suspect I could set it up in Linux by monitoring the battery discharge state, but I'm mostly in Windows 7 and can't find anything.