Northstar Horizon Update

From: Anthony Clifton - Wirehead <wirehead_at_retrocomputing.com>
Date: Sat May 22 15:46:51 1999

Just wanted to share an experience. The Northstar that I got working
this week up and quit working on me Thursday night. For no reason,
it just stopped printing the NSDOS 5.1 banner on boot. I checked
SINP on the bus and it was looping, I checked for read errors on the
controller and found none.

I swapped the 3 1488 line drivers around, then the 1489s for no reason
and finally the 8251 USARTS to see if the problem would move from port
to port. No dice. I checked for chips that may have popped out of
sockets. I pulled chips and reinserted them. I pulled cards and
reinserted them. Still nothing. I changed terminals. Nothing.

Finally, it occured to me that I had flipped the chassis over to put
some new rubber feet on the bottom and wondered if I could have shifted
something, like a loose screw or nut. So I removed the motherboard and
looked underneath. LO and BEHOLD! A previous owner had replaced an
LS series chip and its socket and had not CUT OFF the excess leads on
the bottom of the board!!! When I shifted the machine, it pushed the
leads against the bottom of the chassis effectively grounding them!

Once those were clipped and a piece of anti-static foam inserted beneath
the motherboard, the machine now talks to the terminal FAR more reliably
than before.

So my Tip for the Day: When restoring a machine that isn't working,
check out the user mods FIRST! They're the most likely suspect IMHO.

Note: The machine still isn't acting 100% perfect. Sometimes it takes
a reset or two to get it to boot properly. Is the N* A2 Ram-16 card
known to be a bit flakey? I have an A3 that needs a capacitor replaced
and I'm wondering if the A3 fixed specific problems with the A2. The
problems it seems to be having look like memory problems to me.

Thanks...

Anthony Clifton
Received on Sat May 22 1999 - 15:46:51 BST