Date   : Fri, 15 Sep 2006 11:25:32 +0100
From   : "Ian Wolstenholme" <BBCMailingList@...>
Subject: Re: Domesday Disaster

Thanks for that, it may have to be my next option if my latest
"method" doesn't work.  I haven't been inside this LV-ROM player,
it's like the MDFS, if you can break one, you can break another! So
I have shied away from opening up my main MDFS or my working
LV-ROM player for this very reason.

The laser definitely seems to like being near the "bad" sector to
start with if it is going to read it, so I have started splitting up the
final chunk into smaller chunks and saving up to just before a known
dodgy sector and then starting the next chunk from this point.  It
takes a bit longer and sometimes a few retries are required but
it's working bit by bit.

Another curious error which occurs is that if I *DUMP the file
part way through, press ESCAPE and then do *VFS, the free
space map is corrupted with the first 5 entries being replaced with
"FAFAFA : FAFAFA".  This is a bit irritating since I was hoping to
use *DUMP to leave the laser in the right position and then
resume the copying from there but I have to mount the disc
again to get round this error which sends the laser back to the
beginning.

Best wishes,



Ian

----- Original Message -----
From: BRAHMS
To:  "Ian Wolstenholme" <BBCMailingList@...>
Sent:  Fri, 15 Sep 2006 08:00:47 +0100
Subject: Re: [BBC-Micro] Domesday Disaster

Not sure, but another "worth a try" might be to take the lid off and look 
for
hairs in the laser area, these can cause this kind of problem, the head tips
them over and they get in the way at a certain point?

Dom
----- Original Message ----- 
From: "Ian Wolstenholme" <BBCMailingList@...>
To: <bbc-micro@...>
Sent: Friday, September 15, 2006 12:54 AM
Subject: Re: [BBC-Micro] Domesday Disaster


> Of course if I had pulled out the drive tray fully instead of letting it 
> stop
> when it bumps into the A5000 keyboard sitting on top of the Master then I
> would have seen that there is a cut-out at the back of the tray which
> would allow the laser to read any part of the disc when it is spinning! 
> How
> very clever!
>
> I am now getting a consistent error at the same sector, so either the 
> "drift"
> has resolved itself or the dust has settled!  I wish I knew where this 
> sector
> was on the disc surface, I could make sure it's clean!
>
> The *DUMP thing may be a bit of a red herring.  My logic was that you
> deduct the start sector of the file (as reported by *INFO or *EX) from
> the sector number of the error, multiply by 256 and DUMP from that
> point within the file and that's the same location on the disc as where
> the error was reported.  Of course, it's not always the case since
> the file might not be a contiguous block of sectors, and probably less
> likely so on a Domesday disc given the way they are laid out with file
> structure and video content.
>
> So, a bit of an Eric Morecambe/Andrew Preview moment there: "I'm
> reading all the right sectors, but not necessarily in the right order...."
>
> Best wishes,
>
>
>
> Ian
> ----- Original Message -----
> From: Jules Richardson
> To:  bbc-micro@...
> Sent:  Thu, 14 Sep 2006 21:52:01 +0000
> Subject: Re: [BBC-Micro] 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
>
>




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