1771 floppy controller questions

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Nov 21 18:40:49 2001

You'll want to be careful with the early DRAMs, as they used 3 supply rails, and
your tester of 5-volt-only DRAMs may die from application to a 3-supply DRAM.

Dick
----- Original Message -----
From: "Tothwolf" <tothwolf_at_concentric.net>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, November 21, 2001 4:43 PM
Subject: Re: 1771 floppy controller questions


> On Wed, 21 Nov 2001, Richard Erlacher wrote:
> > From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
> >
> > > 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].
> >
> > For troubleshooting possible RAM problems, it's really easy simply to hook a
> > 64Kx8 SRAM on top of the DRAMs, grabbing the addresses before the decoder
and
> > multiplexers, and use OR'd nCAS to the DRAMs as the output enable to the
SRAM.
> > You simply disable the data from the DRAMs by pulling the pins out of the
> > sockets. The result is that your system works using the SRAM, yet you can
poke
> > around all you like in the DRAM array and the associated timing logic.
>
> I bought a used dip style dram tester set about a year ago. It only cost
> me $5, and I figured it might be useful for testing all the old 64k and
> 256k drams I seem to run into in old pcs. I haven't yet had a chance to
> use it yet. Maybe it will help with these old boxes...
>
> -Toth
>
>
Received on Wed Nov 21 2001 - 18:40:49 GMT