Where might I obtain a repair manual for a CLD-M403?

We don't appear to have that exact model in our database but we do have its older sister, the CLD-M90 available here.....

https://manuals.lddb.com/LD_Players/Pioneer/CLD/CLD-M90/

If your focus for repair is mechanical in nature, this manual will be fine as all the M series use the same mechanical systems. If it's circuit boards, they are somewhat similar so you might still be able to utilize the M90 info.

Did you have a particular problem you wanted to inquire about? We might already know the answer to your issue.

Thank you very much. Seems to be exactly what I need.