Date : Wed, 29 Mar 2006 23:02:44 +0100 (BST)
From : Pete Turnbull <pete@...>
Subject: Re: Model B NMI PITA.
On Mar 29 2006, 20:52, Fragula wrote:
> Pete Turnbull wrote:
>
> I have noticed one thing though.. ICs 79 and 80 are 7438 on the map
at
> the back of the AUG, but my board appears to have 7437s, which are
totem
> pole outputs, not open collector.
Well, IC79 pins 6 and 11 are the drive selects, and they're also fed
back to IC83 and 84 (pin 6 in each case) which are CD4013s used to
drive the READY inputs on the 8271. A totem-pole output would have the
wrong thresholds to do that reliably "by the book", but it probably
doesn't matter much in practice.
> > It's possible you have an early PCB that needs some fix to use the
disk
> > interface properly, though offhand I can't remember what the fix
would
> > be (something to do with that 7438 at IC27, and S9).
> Well the problematic ones, One really, the one I've owned for 20 odd
> years, is an Issue 7, but its been home upgraded (everything +
kitchen
> sink) and has been problematic ever since fitting the Econet upgrade.
> The econet has never worked right, though the disk system is working
at
> the mo (or was till i ripped it all off earlier this evening).
IIRC even an Issue 7 has some minor mods for Econet reliability. Did
you do them? I can assure you that if you solder all the right things
in the right places, an Econet upgrade on anything later than Issue 1
will work fine, with or without disk interface as well. I've done
literally hundreds, and what's more, I used to fix the ones the local
ITeC bodged ("Ten K resistors are yellow-black-brown, right?" "Is
there really a difference between yellow and orange stripes?" "Do I
have to solder both ends?" "But nearly *all* the pins were in the
socket!")
I made a lot of money out of the dealer who thought it would be cheaper
to use the ITeC than competent staff, and then sent us the "repairs"
they couldn't fix.
--
Pete Peter Turnbull
Network Manager
University of York