My SFAC stick since the day I"ve got it has oddly been having this habit of making my character just randomly jump which is really irritating. So what could be the reason is it the spring or what? I know fairly little about working on sticks hence the reason why I am asking for an answer and a solution.
-Frankie 
Mod it with a Happ, if it still does that you have a bad PCB, so mod it with a PCB of your choice, as the SFAC is a good box, but sucks stock anyways (Damnit if I had some money I’d fill my empty SFAC with Happ parts…)
Do you hear the microswitch click when you randomly jump? If not then it is probably the PCB.
One of the SFAC sticks I got had that problem.
Probably the joystick actuator is too close to the microswitch (the actuator presses the microswitch but it doesn’t come back completely, therefore the system thinks you’re still holding up on the stick). In theory that can be fixed but I think it’s easier to simply get a new joystick and replace it.
Well I modded it with Happ parts. The start and Select are still stock(Will this make a difference?). I do here it click when I jump. But yeah I’m starting to think it’s the Pcb.
anybody elses SFAC stick not work on some fat ps2s man i hate that. its the pcb i know for sure just not compatible.
The start and select buttons being stock doesn’t make a difference, if they broke the only thing it could effect would be your start and select buttons not working right, they can’t affect directions.
Open up the Happ and see if it returns to center, and click your up microswitch (remember that up is “down” from your perspectice, move the stick up to see what I mean) and see if it sticks or something. If not it’s your PCB.
If it clicks when you jump that means the microswitch for up is being hit unintentionally. Switching the stick to Happ should solve the problem.