I have a keyboard problem with a Lenovo Thinkpad which won't boot
because it detects a stuck key. The error code implies that the
offending key is the numeric 6 key but it's not physically stuck, I've
prised off the keycap and the rubber dome underneath moves freely with
an audible click so I'm assuming it's a short circuit problem inside the
keyboard.

I might be able to source a replacement keyboard but I'd like to check
that there's no other problems with the laptop before doing that. I'm
contemplating disconnecting the ribbon cables for the keyboard and
plugging in an external USB keyboard for testing. Would this be likely
to work and if not is there any danger that powering up the laptop
without its internal keyboard could be harmful?

On Friday, November 25, 2022 at 3:21:12 PM UTC, Mike Clarke wrote:
> I have a keyboard problem with a Lenovo Thinkpad which won't boot
> because it detects a stuck key. The error code implies that the
> offending key is the numeric 6 key but it's not physically stuck, I've
> prised off the keycap and the rubber dome underneath moves freely with
> an audible click so I'm assuming it's a short circuit problem inside the
> keyboard.
>
> I might be able to source a replacement keyboard but I'd like to check
> that there's no other problems with the laptop before doing that. I'm
> contemplating disconnecting the ribbon cables for the keyboard and
> plugging in an external USB keyboard for testing. Would this be likely
> to work and if not is there any danger that powering up the laptop
> without its internal keyboard could be harmful?

99.9% sure that you can power up without the keyboard; and Thinkpads
are about the best laptops to disassemble & remove the keyboard (unless
it's a pretty modern one; I have a T14s with a keyboard problem which
looks like a pain in that regard)

What you suggest is exactly what I would try.

J^n

On 25/11/2022 16:34, jkn wrote:
> On Friday, November 25, 2022 at 3:21:12 PM UTC, Mike Clarke wrote:
>> I have a keyboard problem with a Lenovo Thinkpad which won't boot
>> because it detects a stuck key. The error code implies that the
>> offending key is the numeric 6 key but it's not physically stuck, I've
>> prised off the keycap and the rubber dome underneath moves freely with
>> an audible click so I'm assuming it's a short circuit problem inside the
>> keyboard.
>>
>> I might be able to source a replacement keyboard but I'd like to check
>> that there's no other problems with the laptop before doing that. I'm
>> contemplating disconnecting the ribbon cables for the keyboard and
>> plugging in an external USB keyboard for testing. Would this be likely
>> to work and if not is there any danger that powering up the laptop
>> without its internal keyboard could be harmful?
>
> 99.9% sure that you can power up without the keyboard; and Thinkpads
> are about the best laptops to disassemble & remove the keyboard (unless
> it's a pretty modern one; I have a T14s with a keyboard problem which
> looks like a pain in that regard)
>
> What you suggest is exactly what I would try.
>
> J^n

Thanks. I removed the keyboard and connected an external USB keyboard
and everything worked fine.

Then I shut down, unplugged the USB keyboard and reinstalled the
internal keyboard and was surprised that the BIOS no longer reported a
stuck key. I think there's more to this than being cured by just
reseating the ribbon cables because I'd done that previously with no
improvement but this is the first time that I'd powered up the laptop
without the keyboard so I'm wondering if the stuck key state was latched
in the keyboard driver until it found no keyboard there.

I'll keep my fingers crossed and hope the problem doesn't return.