What am I doing wrong? Is it the media? The burner?
It's the media. Ritek is unreliable. Inconsistent quality.
I've never tried printable discs, but the best I've used is Verbatim (MCC - Mitsubishi Chemical Corporation).
Always use high quality discs kahit mahal. Otherwise, nonsense ang pag back-up kung masisira din agad.
Madaling magasgas at mag-disk error.
Try scratch resistant discs. I've tried Imation Force Field (DVD-R), and it really works (
http://www.imation.com/products/dvd_media/dvd_forcefield_discs.html). Unfortunately, 1 piece free sample lang last year. Still not available in da Pilipins.
But since you buy online, why not try TDK ScratchProof -- http://www.supermediastore.com/tdk-scratchproof-hard-coat-8x-dvd-r.html
How does one perform diagnostics on the burner?
The best diagnostic tool:
Nero CD-DVD Speed (freeware, latest version = 4.51.1) -
http://www.cdspeed2000.com/go.php3?link=download.html