Toshiba Satellite L750D Keyboard Issue - Specific Keys Not Working

[claustrophobist]

Have a Satellite L750D which was working absolutely fine until recently. I had put new thermal paste, a routine task for me, and had reinstalled Windows 10 64. There were no issues and I was able to use the laptop normally after this procedure.

However, out of nowhere, specific buttons do not work , including CTRL, A, S, C and V (and Others).

I thought a bad connection was affecting it so I removed the keyboard and put it back. The problem persisted.

I tried removing the drivers from Windows, but the problem appears to be deeper, as the same buttons also do not work in the BIOS (eg when typing a password).

I tried removing the keyboard cable again, the battery of the laptop and the CMOS battery. Held power button for 60 seconds to reset CMOS. After a reset the problem persists again.

I then decided to update to the most recent available BIOS version, as the current one was severely outdated. The update went fine, but the problem persisted.

I then thought that maybe the keyboard itself is problematic. Luckily I had another Satellite variant sitting around. I tried the keyboard from that one... and the problem persists - on the exact same keys both in BIOS and in Windows. So it can't simply be the keyboard.

I am very confused here. I am certain that I caused no damage to the board , and I am 100% certain that the keys worked at first without problem , as I was able to perform a full installation of Windows 10 and Office, having to use the keyboard to type the product keys for each respective software. The computer was working fine, as it should have been expected to, then suddenly this problem surfaced and has left me perplexed.

I could try to find an identical replacement keyboard, but the fact that the second keyboard tried works and POSTs normal yet does not type the same specific keys is a major concern for me.

Temperatures are fine and the system otherwise has no issues.

What should my next course of action be?

 

[hang-the-9]

Does an external keyboard work OK? If it does, with a second keyboard having the same issues, it is most likely a motherboard issue.

 

[claustrophobist]

External keyboards work fine. Why would the motherboard have a problem though? It worked fine and the problem emerged suddenly.

 

[hang-the-9]

External keyboards work fine. Why would the motherboard have a problem though? It worked fine and the problem emerged suddenly.

No idea why, but that looks to be where the issue is if a replacement keyboard did the same thing and an external keyboard is fine. If you rule out every other possibility, whatever is left has to be the cause.

 

[claustrophobist]

Is there any chance a spec of lint or dust has entered the connector, causing one specific circuit to fail to work? I have to explain why only specific keys don't work, and that's the best I can come up with - alongside short circuits of some kind, or perhaps the connector is gone.

Short of replacing motherboard, at a cost that would not warrant it since for the money a much newer laptop can be bought, I am out of options am I not ?

 

[jr9]

You can remove the keyboard assembly in most laptops and clean them. You could also clean the keyboard ribbon connectors with isoprobl alcohol and a lint free cloth. Finger oils can cause shorts. Damaged keyboard ribbon can also cause connection issues.