T520 Power Button partially malfunctioning

[hoax32]

Hey guys,

I have an issue with a T520 of mine which has me puzzled.
It is a very early T520 which sat stored locked away for almost a decade and is in perfect condition.
For whatever reason the power button does not properly function on this machine and a keyboard replacement did not help to remedy this problem:

The power button turns on the machine but does not function once the machine is actually on.
You can not use it to shut down (confirmed that the function is assigned to it - problem exists in Windows 7 and Windows 10) and the hard shut off function by holding it down for 5-10 seconds does not work either. It is as if the machine does not register the power button input once it is on.
The only function of the power button that appears to be functioning is its ability to power on the machine if it is actually powered off - it will not awake the machine if in sleep mode - only if completely shut down.

I already updated the BIOS and embedded controller to the latest version with no remedy in the problem.
Any suggestions? I am puzzled.

[atagunov]

Hi, you could try and see how the power button on the docking station functions - if you happen to have access to a suitable docking station (and these are pretty chip and quite useful for running x20 and x30 machines).

[hoax32]

Thanks for the response - unfortunately I do not have a dock.

[mikemex]

Replace the CMOS battery.

[RealBlackStuff]

After 10 years of non-use the cup under the power button might have become brittle.
Find any old keyboard from the same manufacturer and replace that cup.
AFAIK any cup from under any letter- or number-key will do.

[hoax32]

Unfortunately I already tested a spare keyboard with the same results.

[kfzhu1229]

Unplug the battery and charger, and then use electrical contact cleaner (or high concentration alcohol if you don't have one, pretty sure you have that because of the environment we are living in right now) and a spare toothbrush to thoroughly clean the contacts of the keyboard connector.
On a Thinkpad you absolutely wanna make sure the battery and charger are both disconnected, or else a fuse blows as soon as the water inside the alcohol touches the keyboard connector!
Since the power button pin is always carrying voltage (unless the power button is pressed down), that pin can very well become oxidised much quicker than any other pin (especially so if you ever had the keyboard connector seated halfway in or pulled out while the laptop is on)
If this is indeed the problem, then it's probably because the oxidised pin is acting like a resistor and the motherboard wants a more extreme voltage drop on the pin to register a press of the power button when the laptop is on compared to when the laptop is off