Speedo "stuck"

So the speedometer on my car is stuck at the 75mph mark. The thing is the engine & trans are out of the car, so I think it's safe to assume the problem is with the speedo head LOL

How hard of a fix is this? I plan on pulling the instrument cluster out at some point this winter/spring, I'm just not sure how how big of a deal this will be to fix. Looking for thoughts, suggestions, fixes, etc. Thanks!