Date   : Sat, 30 Oct 1999 13:45:15 +0100
From   : Philip Blundell <Philip.Blundell@...>
Subject: Re: Further investigation 

Did you say you had swapped the LM319 chips for those in another machine?  If 
not, give that a go.  I guess IC91 might also be faulty.  Assuming the '319s 
are socketed, pull out IC55 and check that you now get 5V on IC91 pin 5.

Also, do you know if the Econet interface has ever worked in this machine?  If 
not, it could be that the upgrade was botched.  The 2% resistors in the 
analogue side are quite critical; some machines had 10% tolerance parts fitted 
which are no good.  Probably worth checking at least the 56K resistors around 
IC55 in any case.

p.