Have you tried testing this unit with a commercially pressed CD just for the heck of it? That you haven't stated.
I know lots of DJ's use MP3's as source for their CD's. Don't get me started on how horrific the MP3 format is, that's a whole other rant. But regardless of the source, are you using quality CD-R discs? Are you using CD-RW? Not everything likes CD-RW and some flat out don't like the cheap CD-R's.
Also, are your CD's burned orange book or red book? Are you using Disc at Once? You should burn in a Disc at Once/Track At Once to ensure a Red Book Audio compatible CD.
It's possible it's a disc problem. It could be a motor problem. It could be a laser problem. It could be a combination of more than one of those issues and even them some other issues.
When I test, I try to get to the most straight-forward one first. Commercially produced CD. Start with that. See where that leads. Then check other stuff. Use a CD you or someone else has burned that is KNOWN good. Test it on a few other CD players too. See if the results are consistent. Again, could be multiple things.
I don't have the CDI500, so I can't trouble shoot that specifically. But, it sounds like a motor issue to me. I had a CD-player fail recently, but it was a 12-year old Sony Discman. Won't spin up anymore. Exhibited the same symptoms you describe. It did this with a commercially made CD, didn't bother testing further.