MPC 2500 f3 and f4 button problem

Hi guys!
I have a problem. My f3 and f4 buttons sometimes work and sometimes they don't... But they always do this in pair. When The f3 doesn't work The f4 doesn't either... Anda when they start to work again it's at The same time... At first i thought it could be The tact switches but since they always work or stop working in pair i eliminated that chance... Any ideas?
Appreciated!

just solder in some new tact switches, should cost you 2 dollars or so and then test it out. if the problem remains, post it up here and we try to help you out.