PX-716UF horrible access times - damaged drive?

vbimport

#1

A bit of background. I recently acquired a factory sealed Plextor PX-716UF external drive. Before using the drive, I confirmed that the drive was indeed new with both PX-Info and QPxTool.

For the most part everything about the drive seems to work great. All transfer tests are as expected. All Plextools tests, including focus and tracking error tests are as expected. When I do error scans on CDs, I get similar values as error scans performed with my Plextor Premium. The one problem I found, however, is the drive is excruciatingly slow when doing “secure” CD ripping. I think I tracked this problem down to poor access times.

Running Nero Disc Speed on numerous factory pressed audio CDs, I get Random Access Time values of 300-500 ms, ouch! Published values for access time by Plextor are < 100 ms. The odd thing though, is that when I do tests with Nero Disc Speed on CD-R data discs, I get Random Access Times down around 95 ms.

So what is wrong with the drive? I originally though perhaps the rails needed to be oiled, but the difference between audio CD and CD-R now has me a bit confused. Is it possible it is some laser degradation problem? I have no idea how the unit has been stored for all these years.


#2

My PX-716A is in the same state :frowning: When I got it, it wasn’t new, but still had warranty seal and burned just few discs. However, it suffers from very long CD recognition and from very long access times. I’ve opened the drive - it was in excellent state inside, looking like new… Then I’ve reconnected the flat cable on OPU and board (it helped me in many cases on old Samsung, LG, LiteOn, NEC and Pioneer drives) - but nothing was changed. :frowning:

There is no doubt, that something is wrong with the drive - but I’m still unable to figure out the reason. :frowning:


#3

Ugg the PX-716 is such a difficult drive. This is my third one (previous two were purchased used for ~$20). The last two had no problem with CDs, but they had all sorts of problems with DVDs, which is why I did not keep them. I thought it was because the drives were heavily used, but perhaps it is just that the PX-716 is a rather inconsistent drive.

For what its worth, my new old stock drive that has terrible CD Random Access Time is TLA 0309 and built in April 2006. It is surprising that Plextor was still manufacturing the PX-716A even after the release of the PX-755A and PX-760A.


#4

Plextor drives are prone to dropping to 8x speed when extracting audio. My Premium-U, PX-755UF & 3x PX-716s have always behaved this way. It isn’t a fault, just that Plextors aren’t actually particularly good CD readers and very intolerant of less than perfect/pristine discs. They seem to be programmed to drop the speed at the first sign of difficulty and are very reluctant to increase it again.

Also, many drives are significantly slower when extracting audio securely rather than normally. Which audio extraction software & settings are you using?

Regarding the access times, I haven’t tested audio CDs vs data CDs myself. But audio CDs (CD-DA) use a completely different file system/disc format to data CDs. Data CDs have much better error correction, but this requires much more disc space.

Famously, Norio Ohga (vice-president of Sony) demanded that the discs should be able to hold his favourite piece of music - Beethoven’s Symphony No. 9 (specifically the 1951 Bayreuth Festival performance) - so its capacity had to be increased from 60 minutes to 74.

To achieve this the physical disc size was increased by 5mm, but this wasn’t enough and more capacity had to be found somewhere. So unlike data CDs, audio CDs don’t have a checksum to confirm that the data has been read correctly - hence the need for secure ripping. (In any case you wouldn’t want a CD player which kept pausing while it went back and re-read the disc, much better to carry on and try to hide any audible errors.) And it is much more difficult for the drive to find the correct location on the disc - which is why drives have different read offsets.

I expect this explains the high access time you are seeing when testing with an audio CD.

In normal use the access time is not important for audio CDs, as they are read linearly with random seeks are only required when skipping tracks.

What does matter is that the drive is able to read the disc consistently. Audio CDs are actually read in small bursts - not in one continuous stream as one would imagine, like the stylus following the groove in a record. Many older drives (including extremely expensive hi-fi equipment) didn’t have a consistent read offset, so when the drive started reading the next burst it wasn’t actually reading from the intended location on the disc. The result was a small step in the waveform which could be heard as a click. (You can replicate this by deleting a small section of audio using your favourite audio editor.)

So it would make sense for a drive to deliberately opt for slower, but more accurate movements of the optical pickup when an audio CD is detected.