The problem is, when you try to burn a dvd at a speed lower than its rated speed, for example, burning TY02 at 4X or 2.4X, you will end up with coasters. However if you burn TY02 at 8X or above, you will get successful burns.
I have tried Taiyo Yuden DVD+R 8X from Rima, Maxwell DVD-R 4X, and Benq DVD+R 8X(Daxon) on 3 Benq 1620a with firmwares B7L9, B7P9, B7T9, BTU9, with DVD Decrypter, Alcohol 120% and Nero all resulting in the scenario stated above.
Try ripping a DVD into ISO, burn that ISO back to DVD format at speed lower than the certified speed, and then verify the disc.
This problem does not exist with Plextor PX-716A when I tested it. Can anyone help me figure out what is going on?