Got MPC2500 used, need to know what to check

Hey its me again,

so I got the MPC2500... I got it used for a good price... heres the problem, I need to check to see if everythings working good, i still have little to no experience on the thing so im unsure what im looking for... what do you guys think I need to check.

also I noticed that (maybe) some pads (topmost row) are not ideally sensitive... like when i turn off full level some play absolutely no sound, but when im on full level everything is okay... Im thinking that this (maybe) can be altered inside the machine so how do I do that to check that they are in good workng condition (or need replacement) ??

Thanks for your help everyone, wish me luck on this journey

I'd do a factory reset as a starting point