Brother MFC-7420 prints dirty pages

[singulargal]

I have a brother mfc-7420 that is printing dirty pages. I recently replaced the toner with geniune brother tn350. When I check the drum after printing, the drum is covered with toner. I tried another new tn350 with the same results. I put the same drum/toner units in a different mfc-7420 and it prints fine. Any ideas about what's wrong with the MFC?

[MichaelTech]

You may have to clean the contacts for the drum! Can get very dirty inside.

[singulargal]

Thanks for your reply MichaelTech,
would blowing the cavity out with canned air suffice, or are there specific instructions to clean the contacts for the drum?

[julie.severn]

Don't mean to sound funny, but we have a Brother MFC 7420 and the Toner is a TN2000. Just a thought, though perhaps yours is a colour printer, ours is only black.

[singulargal]

Julie,
Thanks for taking the time to reply!
no, it's a monochrome unit. and the drum and toner that came with the device were a DR350 & TN350, and the other MFC-7420's using the same consumables print just fine.
I'm just stumped why the drum stays covered in toner when printing. different drums & toners give the same result when used in this particular unit but print fine in others, so the problem must be with this MFC.
Is anyone out there familiar with this symptom?