Date   : Fri, 02 Dec 2005 10:53:07 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Order of Acorn Computers?

Richard Gellman wrote:
> Jules Richardson wrote:
> 
>> I also feel that the US-spec BBC B should really go on there as a 
>> separate machine, same with the Domesday setup, just for completeness 
>> sake (I don't *think* you could buy the bits separately to roll your 
>> own Domesday system).
> 
> *most* of the Domesday system is standard parts, essentially:

Sure, but it depends on the focus of the list - if it's pre-packaged machines, 
  then the Domesday system probably qualifies at least as much as the Business 
Computer range. After all, you could go out and buy a Cub screen, B+, 
Winchester bits, copro etc. separately and just be without the case. Just as 
you could presumably buy everything for the Domesday separately except the 
player (and the media :)

> One reworked Acorn SCSI hostadapter board. Take the hostadapter board 
> from an Acorn winchester unit, and replace one of the buffer chips with 
> its non-inverting counterpart. Then wire it into the internal modem/test 
> connector on the Master's main board (nasty looking slot-ish connector 
> on the left-hand side, next to where you normally put the CMOS batteries).

Interesting; must look at the schematics. I did do a test yesterday to prove 
that ADFS in a Master won't drive a hard disk via the Master (Domesday) SCSI 
controller - it appears to be coded for the BBC B variant only (as your email 
now suggests).

> One Acorn trackerball - You can replace this with an AMX mouse, just 
> swap the signals coming from the left and right buttons.

Think they were Marconi units anyway, and probably available off the shelf 
somewhere.

> Acorn "Domesday" Monitor. While somewhat flashy at the time (and 
> provides a stonking picture over any 14" TV today) it is essentially 
> just a TV with no UHF tuner.

Actually, isn't it the same as the later Acorn displays (from the Arc era) - 
those had SCART, and I've certainly used one with my Domesday setup before. I 
don't think all of them will handle composite in though; most only do 
component RGB. Seems to be a lottery as to which you get. Think they were 
rebadged Philips too, and often seen on other machines (Amiga springs to mind)

Why they left out the circuitry in the Domesday player to provide mixed video 
signal on component RGB I'm not sure, given that this is what 90% of displays 
will handle.

> Now the hard part: One Philips VP-415 LVROM Player.
> This is actually a VP405, with a hack

Quite some hack ;)

> The 415s were made for the BBC/Acorn especially for the Domesday system 
> (although they also work with the RM Nimbus domesday variant), hence 
> their rarity.

There's still a fair number around, but almost none of them work. Build 
quality on the players is about the worst I've ever seen in anything.

> To summarise, you could probably build the majority of the Domesday 
> system without too much difficulty (a little soldering may be required), 
> but you will need to find a VP415 from somewhere.

At the time, and the media. And the VFS ROM. Neither would be easy to get hold 
of without going through Acorn.

> Incidentally, the SCSI board in the Domesday Master has a second circuit 
> on it (separate from the SCSI part) that provides an alternate 16Mhz 
> clock through the links near the UHF modulator. Since the Master 128 
> already has a 16Mhz clock, anyone have any idea why a second clock is 
> provided to override it? 

Possibly stability reasons to improve genlock performance? There's certainly a 
lot of image tearing whilst the genlock syncs the beeb and LVROM video; maybe 
it minimises this?

Just a thought, without digging out player service manuals and stuff!

cheers

Jules