Date   : Sun, 14 Aug 2011 22:49:48 +0100
From   : pete@... (Pete Turnbull)
Subject: Advice on restoring a dead Beeb?

On 14/08/2011 15:33, Rick Murray wrote:

>> what happens at startup and in what order. However, we don't know 
>> for sure which version of the OS is involved and we are missing
>> some
> 
> If it is a mask programmed ROM type HN613128 and (C)Acorn, it is 99%
>  going to be MOS 1.2.

Chris's Beeb has MOS 1.2 and BASIC 2 in original Acorm mask ROMs.  It's 
not a MOS mismatch etc, as the Beeb was tested before it was shipped.

>> By reconfiguring jumpers, I think it is possible to have the OS in 
>> four parts in what would normally be the paged ROM sockets and have
>>  only one language ROM available in what would normally be the OS
>> socket.
> 
> Yes, I believe that was for development when MOS zero-point-zero was
> in a bunch of 8K EPROMs.

MOS 0.1, actually, and it was 4 x 4K EPROMs (2732s).

> Not entirely certain why this option would be continued into
> production hardware. I guess it is one of the many little quirks of
> the BBC (like why didn't composite video output colour in the first
> place?).

Because the first production machines did actually ship that way, with 4 
EPROMs for the MOS.

As to the video, it's because adding the colour burst signal actually 
degrades the monochrome one. Early boards have no innate provision to 
add the colour burst and you have to solder a capacitor; later ones have 
the capacitor and often a pair of Molex pins to jumper.

> It is a shame the original poster "reseated" the various things. I'd
>  have thought powering up first would have been a good idea, and only
>  mess around inside if it is non-functional. [caveat: well, the very
> first thing is to give it a gentle shake while rotating it to check
> nothing got in, and nothing (video ULA heatsink?) has fallen off]

I thought Chris did, and did the reseating because the Beeb didn't power 
up after it's travels.  Oh, and IIRC, the video processor is a VidProc, 
not a ULA, so no heatsink required.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York