Date   : Fri, 29 Oct 1999 20:56:37 +0100
From   : Philip Blundell <Philip.Blundell@...>
Subject: Re: Further investigation 

>Further investigation has narrowed the problem down a little more. I am not
>getting a wave form to pin 3 of 68b54 from pin 12 of IC 94. The IC is ok,
>and pin 7 is generating it's wave form. R61 has 5v on it being pulled down
>on the other side as expected. Bit hard to measure resistors when in situe.
>
>Capacitor C23 could be suspect. Anyone know how I can test this with an osci
>?

Now I'm confused.

Pin 3 is the 68B54 receive data input.  Lack of signal there would cause the 
Econet not to work but it shouldn't be able to lock up the machine.  My 
suspicion for the lockup, if the 68B54 itself is in the clear, would fall on 
the IRQ gate circuitry involving IC97, IC01, IC27.

The area involving the second LM319 (whose outputs are connected to the R61/
C23 combo) is the collision detect.  I don't think C23 is worth worrying about 
at this stage unless you have a particularly strong reason to think it's 
faulty.

p.