21 Nov
2001
21 Nov
'01
9:43 a.m.
On Wed, 21 Nov 2001, Richard Erlacher wrote:
From: "Tony Duell"
<ard(a)p850ug1.demon.co.uk>
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
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.