1771 floppy controller questions

From: Tothwolf <tothwolf_at_concentric.net>
Date: Wed Nov 21 18:05:24 2001

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 - 18:05:24 GMT