Date   : Wed, 21 Oct 2009 23:36:18 +0100
From   : bbcmicro@... (Ian Stocks)
Subject: BBC Model B Issue 3 Circuit Diagram

Pete Turnbull wrote:
> On 21/10/2009 20:54, Mark Haysman wrote:
> 
>> 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.
> 
> I don't have suitable scanner access right now, but I do have the 
> diagram, and I've done these upgrades a few times myself.  The clock 
> parts are:

[snipped component list]

Looks like my guesses were about right.

Clock link 4 = 600K?

> The terminator parts (it's a proper active terminator) are:
> 
> R54 - 100K
> R56 - 100R
> R42 - 56R
> R43 - 56R
> D3 - 1N4148 (with the cathode connected to the junction of R56/C22/R42)
> C19 - 10?F electrolytic
> C22 - 10?F electrolytic


Interesting, I presume this is just teminating the data side, Not enough 
parts for both the data and clock.

Ian.