Grundy Newbrain Computer wont power up.

From: Keeble, Andy <>
Date: Wed May 13 04:51:07 1998

> -----Original Message-----
> From: []
> Sent: Tuesday, May 12, 1998 7:15 PM
> To: Discussion re-collecting of classic computers
> Subject: Re: Grundy Newbrain Computer wont power up.
> >
> > 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
> >
> > 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.
        [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.

> >
> > Turning on, the LED display flickers and goes blank (although the
> manual
> Actually, it's a fluorescent anode display (see the other
> thread...)...
        [Keeble, Andy] Indeed, I only saw a quick flash on power up,
and presumed it was led. When I opened it up last night I got a better

> > 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.
        [Keeble, Andy] The PSU says something like +6v +12v and -13v. I
found the +12v ok, but the other two outputs are showing +20v, so I
guess its a voltage reg problem. (These are offload values).
> 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
Received on Wed May 13 1998 - 04:51:07 BST

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