Reasons for the failure of the Fn button on the laptop keyboard?

Question

Do it yourself

Good day.
Today was a free day and I decided to do a thorough cleaning of the laptop's cooling system.
The laptop is called Acer TimeLineX 3820TG.
I have rich experience in disassembling and assembling without consequences, therefore, without any problems, I disassembled, cleaned the space between the radiator and the turbine from dust. Collected. As a result, there were no extra details.
I downloaded my favorite Ubuntu 14.01 and decided to update the system one more time.
The system is updated and the laptop is restarted. That's just the brightness and volume are no longer adjustable. Ubuntu was the first to be suspected, but dancing with a tambourine did not work.
The suspicion began to creep in that it was not about Ubuntu and therefore took out a native hard drive with native Windows 7HB.
Loaded Windows. The button refused to work. I turned off the laptop and removed the keyboard, wiped the contacts and put the keyboard back in place. The result is negative.
Just in case, I checked all the other buttons on the laptop keyboard - they all work except Fn.
In what there can be a business and what else it is possible to make diagnostic actions?

Answer 1

Most likely, the corresponding track in the keyboard membrane was bent, interrupted, burned out, or simply was defective.
A simple diagnostic is to find the same laptop or the same keyboard and check if it's the case. If so, then Claudia is a replacement.
Complicated diagnostics - if possible by design, then trace the path and try to close it with a thin (VERY thin) needle away from the button. If it works - Claudia for replacement.
Actually, Claudia is a replacement with a probability of 99.99%

Answer 2

Ilya , thank you.
Your hint gave vent to thoughts and I found what the problem is. It turns out that the cable was damaged at the very tip, which is inserted into the connector on the motherboard.
To check my guess, I took a tester and there really was a break in contact.
Because the contact is external and is in contact with the contact in the connector, then it was decided, as in the good old days with processors, to draw a track with a graphite pencil.
The gap was covered with a pencil, the cable was carefully inserted into the connector and fixed.
Checked work. Everything works great.
Thanks everyone for the replies.