S2815dn: a-4 (Xero) from Pitch Configuration Chart "and then locate the cause of the problem"?

Hello all,

We noticed pitched dots on the output today.  I printed the pitch configuration chart for it.  My image measures from "START" to a-4 (Xero).  I have a repeating pattern of dots all down the page on my prints.  I pulled up the manual and it vaguely says:

"Compare the pitch of the spots on your output with that on the Pitch Configuration Chart, and locate the cause of the problem.
Is the cause of the problem located?"

Yes, but "a-4 (Xero)" doesn't tell me if it is a fusing unit or drum cartridge.  Please tell me I can clean this thing.  The only thing in the manual that says anything about cleaning is for the paper rollers.

Thanks!
Erin