1771 floppy controller questions

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Nov 21 18:48:22 2001

Back in the very late '70's a product similar to flex PCB material was
introduced as a replacement for a ribbon cable, that fit in a 20-pin SIP socket,
in this case, yet weren't custom circuits. I've got some of that stuff around,
as a sample pack I got back then yet haven't used. Unfortunately, when I opened
them to examine 'em, I didn't save the label, so I can't give you a product
name. I thought of this bacause ribbon cable soldered to PCB's always seemed to
me to be a source of trouble. I had keyboards connected with soldered ribbon
for some time and it seems to me that I was frequently restripping and
resoldering, while those attached with connectors occasionally required that I
check that the connectors were securely plugged, but nothing else.

Dick

----- Original Message -----
From: "Tothwolf" <tothwolf_at_concentric.net>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, November 21, 2001 5:05 PM
Subject: Re: 1771 floppy controller questions


> On Wed, 21 Nov 2001, Tony Duell wrote:
>
> > > It has been a number of years since I powered them up. Right now I think
> > > they are both sitting disassembled in a couple of large boxes. I'm in the
> >
> > When yopu have time to get them out again, let us know (or let me know),
> > and we can discuss troubleshooting them.
>
> It's more a matter of room than time right now, as my old "shop" is packed
> floor to ceiling with computers, parts, and so on. My benches are also
> currently covered up with even more parts and boxes.
>
> > > process of construction of a building just for my old hardware, so once
> > > that is done, I'll pull both of them out and bench them and see what their
> > > problems were. I think the model 3 would start up, but just plain lock up
> > > about the time it was going to boot. I think it may be a ram problem. The
> >
> > Mybe RAM. Most disk problems on the M3 and M4 are either the 1793 chip
> > (I've had to replace a couple) or more likely that infernal ribbon cable
> > between the CPU board and the disk controller. If you don't care about
> > your machine being unoriginal, you can use 40 way IDC cable and
> > connectors to replace it (just use 1 row of pins in the connector to
> > replace the 20 pin SIL socket on the CPU board or disk controller).
> > You're only using 20 wires in the cable, which is something of a waste,
> > but it's the easiest fix I've found [1].
>
> I seem to remember one of these machines had a chip in one of the ram
> banks that was missing a pin. It looked like it had corroded off. It was a
> ceramic package with gold plated leads.
>
> The ribbon in both computers was in somewhat bad shape. I was planning to
> replace it with either a similar cable, or an IDC cable, as you suggested.
> My model 1's keyboard cable had the same problem, and I replaced it with a
> short bit of ribbon cable soldered directly to the boards. I'm planning to
> replace that again with something better the next time I work on it.
>
> > > model 4 didn't power up at all if I remember correctly.
> >
> > In which case check the outputs of the power supplies -- both of them --
> > before doing anything else.
>
> I really don't remember if I got that far with the model 4. I may not have
> even checked the 2 switching supplies, since at the time I bought it, I
> didn't have any free time to spend on troubleshooting.
>
> I think I saw some sort of temperature alarm/sensor plugged into the
> output of one of the supplies in one of these machines. Was that a 3rd
> party add-on or something that came standard?
>
> -Toth
>
>
Received on Wed Nov 21 2001 - 18:48:22 GMT