The rotary dial / pushpot on my CDJ 400 allows me to scroll through tracks but when I click the dial in it does not select the track.

I have replaced the part myself with a genuine Pioneer DSX1056 however the problem remains - I am able to scroll through tracks but not actually select them which means there is an issue elsewhere on the motherboard

Has anyone experienced this and can anyone suggest what could be causing the issue and any ideas for a fix?

PS. this is the first time the unit has ever been opened

Thanks !!