Date   : Wed, 21 Oct 2009 21:45:39 +0100
From   : bbcmicro@... (Ian Stocks)
Subject: BBC Model B Issue 3 Circuit Diagram

Mark Haysman wrote:
> Hi folks.
> 
> Does anyone have a scan of the Circuit diagram for an Issue 3 Board? I 
> specifically need to know the parts around the Econet area, and where/how it 
> allows you to add an onboard clock, as well as the jumper settings.

Can't help with the circuit diagram, but does this tell you enough about 
the components for the main interface:-

http://www.heyrick.co.uk/econet/interface/bbc_b.html

 From looking at the atom/system econet circuits and seeing what is left 
after using the above page. I'd guess IC90 - 4017, IC92 74LS74. S6 is 
f/4,f/2 jumper. S5 clock enable/disable jumper. S3 clock speed select. 
(I'm using the pic from http://acorn.chriswhy.co.uk/Pics/BBCA3FL.html as 
component id reference)

I'd guess the components near SK7 are the teminator bits. D3, C19, C22 
etc. Can't be hard to trace out the circuit. I can't see where the other 
Diodes for the teminators are, but the pic is a bit fuzzy around there.

Atom Econet circuit diagram for reference - 
http://bjh21.me.uk/acorn/circuits/circuits.html

Any help?

Ian.