In March I posted a thread titled "Is my Happ trackball dead?". Just wanted to post an update to this issue.
Background: I bought a SlikStik Classic with Happ trackball in September of 2005. Earlier this year, the trackball began to fail. It would no longer track vertically. It died over a period of days.
I emailed SlikStik and they told me that Happ was issuing a replacement optical board for their trackballs. The peeps at SlikStik sent me one at no charge. I installed it in about 5 minutes and the trackball is as good as new!
So if your trackball has stopped tracking vertically, this may be the issue.
Cheers! The Aladdin's Castle Arcade Machine is still going strong!