Hp ProBook x360 440 G1 keyboard types extra characters

[Spyros_123]

Recently I replaced the power connector board and cable of my laptop, and to do so I had to disassemble most of it and surely disconnect the battery. After an otherwise successful replacement, I noticed that the keyboard started to produce extra characters for some keys, e.g.

t produces tb

b also produces tb

y produces yn

n also produces yn

x also presses Caps Lock

Caps Lock also presses x

z produces z` (an extra quote)

At the beginning I also noticed that:

Enter also presses F12-Sleep

but after some time this is not happening any more. However the problem persists for the rest of the keys mentioned earlier.

The same happens in both Windows and the BIOS Keyboard test.

I read a lot of relative posts on the internet and decided that it was a hardware problem.

So I bought a new keyboard and replaced the old one.

But, unfortunately, the problem persists !

I connected an external USB keyboard and works fine !

I have tried to disconnect the battery again (several times) but with no effect.

I removed the BIOS battery (resets BIOS options to defaults) but with no effect.

I updated the BIOS to v. 1.26.00RevA but with no effect

I also updated the hardware diagnostics but with no effect

I try cleaning the film connector of the keyboard of both the old and the new keyboard but with no effect

It seems like it IS a hardware problem but on the motherboard side. But about that:

- Replacing the laptop's  motherboard is very expensive

- I am not convinced that it cannot be solved in a soft manner.

So any help on this could be valuable ...