The A button on my HRAP EX doesn’t work. All the other buttons are fine though. Tried it on my laptop earlier. All buttons except A work. Can I get any suggestions for a solution? 
Happened to me too. I replaced all the buttons with sanwa. There’s a tutorial around if you google it.
In the tutorial, they say you have to dremel off the tabs, which sucks for people without a dremel. I found that a large metal file works just as well, for just a little bit more elbow work.