Date   : Thu, 14 Sep 2006 21:52:01 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Domesday Disaster

Ian Wolstenholme wrote:
> A bit of soapy water seems to have done the trick partly.  It
> appeared to have the effect of moving the disc error further away
> from the original place, each rub down with a soapy teatowel was
> giving me about 2,000 extra sectors!
> 
> *DUMPing the file from a couple of sectors before the "bad" sector
> also seems to help, I am not sure why this would be.  Maybe *DUMP
> is more tolerant than an OSGBPB call but that wouldn't explain why
> OSGBPB continues past the error on the next attempt.

Hmm, that is odd - it almost sounds like an alignment problem drifting over 
time, where if you seek to about the right place first it does better than if 
you seek to block 0 and do a linear read of the whole disc from there.

If you've got the remote, you can kick the player into a diagnostic mode where 
it'll show failure information on-screen whilst you access it over the SCSI 
bus. Unfortunately I can't remember how the heck you do it now, but someone 
else on the list may recall (if not I can go hunting via google groups; I'm 
sure I've mentioned it over on c.s.a.h in the past).

Having said that, memory says that the VFS error codes are pretty good - a lot 
better than just "read error" - and so if you have the manual it may give some 
useful info as to the exact problem.

> Next silly question - if the laser is reading the underside of the disc,
> how does it do this given that the drive tray obscures most of
> the disc surface?  There is probably a very simple explanation to
> this given that this is most likely how CDs & DVDs work as well,
> I just can't think of it at the moment.

:-)

Think of a 5.25" floppy - that manages with only a tiny window through which 
to access data too. The tray in the VP-415 just has a cut-out in the right 
place so that the laser can see the disk, and the laser tracks in and out on a 
'sled' much the same way as a floppy drive's head assembly does (it's actually 
a little more complicated, as there are various servo-controlled mirrors in 
the LV player to focus the laser beam a lot better than a floppy drive's head 
can 'focus' on the disk surface)

Incidentally, I presume that CD and DVD players have a similar mirror 
arrangement - don't know for sure, though.

cheers

Jules