Thinkpad T400 keyboard issue

[pennyhu]

Hello,
I've got multiple issues with an old T400 with a new keyboard replaced last year. When I type certain characters it types double characters. For example: v is /v, 4 is 04 and so on. It does this only for certain characters, others are fine.

I tried an external keyboard and that works fine. I tried an external bootable USB and the same happens on the external USB OS(ubuntu 20) with the internal keyboard.

So i ordered a new keyboard and they sent me a T410/T420 keyboard which doesn't fit. I am returning it. But still the issue of 4 is 04, g is -g is there even with the T410/T420 keyboard. Could it be something with the motherboard?

ADMIN EDIT:
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[TPFanatic]

very interesting that the failure replicates across different keyboards.

if with a third (hopefully correct) keyboard the behavior replicates I would concur there is something wrong with the motherboard (the nervous system of the PC) itself and I would consider retiring or using the T400 in some way that wouldn't drive me crazy with a malfunctioning keyboard.

[RealBlackStuff]

Welcome to the Forum.

That sounds very much like a cheap Chinese knock-off keyboard.
FYI: Keyboards between the T60/T61/Z60/Z61/T400/T500/W500/X200 are interchangeable.
So to check, maybe borrow a KB from one of those?