First, make sure you haven't accidentally turned the balance know all the way to the left.

Then, try reversing the CD to pre-amp L/R cables. Then put them back. Then reverse the pre-amp to amp cables as well.

Since you've already tested the speakers, if no configuration fixes the right channel (and possibly breaks the left), then the right channel on your amp is busted. Work backwards from there to figure out if there is a problem on the pre-amp or CD player. (If th CD has a variable out, you can try connecting directly to the amp as a separate test.)

Ultimately the problem could be as simple as a blown fused in the amp or pre-amp. Something more you probably need to take back to the shop or factory.

HTH