Technics Sl-DZ1200s skipping on one deck

Hi there I've got a pair of Technics Sl-DZ 1200 CDJs and one of them is skipping on every CD I try and play. It's almost like someone has put their finger on the platter for about a second so it sounds like it's being scratched. I've tried the same CD on the other deck and it works fine. I've swapped the leads over and they all work. I've taken it to 2 separate repair shops both of which say there's nothing wrong with it and it plays perfectly ok in their shop. I even brought my own CD in and they said it played fine, but when I bring it back home and set it up the skipping on every CD I play starts. Any ideas would be appreciated; it's driving me mad!!