12 May
1998
12 May
'98
9:51 p.m.
-----Original Message-----
From: ard(a)p850ug1.demon.co.uk [SMTP:ard@p850ug1.demon.co.uk]
Sent: Tuesday, May 12, 1998 7:15 PM
To: Discussion re-collecting of classic computers
Subject: Re: Grundy Newbrain Computer wont power up.
[Keeble, Andy] I only had a quick look at it the
previous
night, but had a bit more in depth look last night. It does look like a
PSU problem, and yes the PSU looks straghtforward enough.
Can anyone help me bring an old British Computer back to life.
Last night I bought a early 1980's Grundy Systems Newbrain "AD"
computer
from an advert in the local newspaper.
(See http://www.ndirect.co.uk/~e.tedeschi/picts/newbrain.jpg)
The machine is in good condition, with original manuals, cables,
psu,
and even some software.
Unfortunately it wont power up.
I have the Newbrain schematics somewhere if that would be any help.
Unfortunately I don't have schematics for the PSU, but I think that's
a
pretty simple linear unit.
Turning on, the LED display flickers and goes blank (although the
manual
Actually, it's a fluorescent anode display (see the other
thread...)... says it should
do this, although I don't get a test pattern which I
think I should) On the Television/video output I just get a white
screen.
Does anybody know if these machines suffered from any common faults?
Check the PSU. The easiest way to do this is to check the 3 supply
lines
at the 4116 DRAM chips (+5V, +12V, -5V). If any are missing or
incorrect
then the machine won't power up. Check the inter-board ribbon cables for broken wires
(they're solid
core
and break easily).
[Keeble, Andy] I will check that, but I suspect I may have
already found the fault, due to the high readings from the psu, just
hope it has damaged any chips in the machine?
Apart from that, if the PSU is OK, you're going to
have to
troubleshoot
this one starting at the Z80 (what is it doing) and working through
the
logic. I don't know of any stock faults on these machines.
[Keeble, Andy] I
thought before spending hours, I would ask
folks on the mailing list, just in case there were any common problems.
I used to work in a computer shop in the early 80's and several makes of
machines came in with the same fault. We didnt deal with Newbrain back
then, so I didnt get any experience of them. If I get the PSU working,
and find I need a schematic, would you be willing to scan a copy and
email it, or photocopy and post it (I would pay any expenses). There
seems to be little info about the Newbrain on the net, and I guess not
that many still exist, so it seems a shame not to try and put some
effort in trying to get this one working again.
-tony