Date   : Sat, 13 Aug 2011 15:07:54 +0200
From   : rick@... (Rick Murray)
Subject: Advice on restoring a dead Beeb?

On 13/08/2011 02:34, Peter Coghlan wrote:

> This is a pretty common failure mode. Unfortunately, almost anything
> could be responsible. Can you let us know what advice you have followed
> so that we know what you've tried or eliminated already?

Is there a step-by-step guide for this available?

There are, IIRC, a number of small gotchas - for example you can't try 
starting the Beeb without its keyboard, and you can't just pull out the 
FDC to ensure it isn't that (there's a link to be changed somewhere?).


> That's a good start. However, when I power up my model B, the caps lock LED
> comes on and stays on and the shift lock LED flashes briefly before remaining
> off.

Yup, I'm reading through the disassembly, and it looks like:

   -> start
      init cpu/interrupts
      clear memory
      caps on, shift undefined
      examine keyboard (links and Ctrl key)
      set up page 2, page 0
      init vias and acia, and adc
      clear sound channels
      set up serial ula
      interrogate ROMs
      if speech - set up
      bring up display
      set up some other internal stuff, printing "BBC Computer"
        and possibly "16K"/"32K" afterwards; following the memory
        size is the VDU7 that is the second part of burr-bip.

Given the VDU7 bip is optional, I would imagine the "clear sound 
channels" silences things. This would perhaps narrow the fault down to 
the VIAs, ACIA (serial) and ADC.

Of these, the user VIA, ACIA, and ADC are optional (IIRC the Model A had 
none of them).

Thus it look like we might be looking at the system VIA as being the 
source of problem - and the #1 thing here is the keyboard connector 
itself not being correct and/or corroded.

The system VIA implements a sort of "slow bus" for talking to specific 
hardware. Refer to the Advanced User Guide for the details.


> Except in really odd cases, the MOS lives in the fifth from the left ROM
socket.

Eh? I thought the left ROM socket was ALWAYS the MOS (extended 
addressing capability or something), followed by BASIC, followed by 
three empties for inserting goodies like DNFS, View, and the like.


> I'd be surprised if the MOS is corrupted.

Ditto. I've yet to experience a ROM (or, for that matter, EPROM) failure 
that wasn't my own fault - like plugging it in upside down, or 
quick-programming that didn't quite "take".


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...