Interesting problem with Sony DRU 710A

[diskdocx]

Bought the 710A in the fall shortly after release. Had a DRU500A from shortly after launch, and had been very pleased with it. Lately I have been getting burn errors using Nero - mostly that it cannot finish disc write at once. I notice that when looking at the burned side of the disc, there are 1 or more 'skips' in the recording surface - almost as if the laser jumps while writing.

Now the interesting thing is that most sectors of the disc are readable, but obviously it is corrupt where this skip occurs. Since these are data discs, I can read info before and after the skip.

This error has occured in the past month or so, and when it first happened I downloaded CDCheck and ran it. Fortunately, this error does not always occur. But out of interest, I ran CDCheck on some old data DVD, and almost every one has multiple points of corruption. THe data cannot be read back of that disc.

However, if I put the disc in my 5 year old Toshiba DVD-ROM, it not only reads all the data, but CDCheck returns a 100% clean disk (with the exception of the more recent discs with the skips visible).

So my questions are;

1) Why is the DRU710 returning so many errors and unreadable sectors on discs that are read fine in the Toshiba drive? If this was truely corrupt sectors, wouldn't CDCheck at least return a warning? (In otherwords, it seems that it is a read problem, not a write problem for these discs)

2) What is the likely explanation for the more recent skipping phenomenon while burning? Don't think its software (Nero), or discs (Memorex 4x). The computer has over 1gig of RAM, and I'm not running anything else while burning.

Is it possibly a defective burner? Shouldn't be worn out as I don't think I've even burned 100 discs so far. Perhaps the laser is out of alignment?

Any thoughts/suggestions? Thanks