1771 floppy controller questions

From: Tothwolf <tothwolf_at_concentric.net>
Date: Wed Nov 21 17:43:18 2001

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 - 17:43:18 GMT