[vcf-midatlantic] IBM PS/2 Floppy Blues

Jonathan Gevaryahu jgevaryahu at gmail.com
Sat Aug 6 23:40:21 EDT 2016

Does this model of PS/2 use a ds1287 rtc/nvram module?
I know at least the PS/2 55sx does, and replacing a dead original ds1287 
rtc/nvram with a ds12887a does not work (but ds12887 non-a should work) 
due to a miswired pin on the socket on the mainboard (the /CLR pin on 
ds128(8)7A is N/C on a ds128(8)7, and is wired to +5v, which you'd think 
would be fine, but 5v drops to 0v when you turn the power switch off and 
clears the nvram contents; due to a different bug (using a base-0 
checksum perhaps) if the nvram is cleared like this the system disk 
cannot correctly restore it, if you try the system always dumps to BASIC 
no matter what; to restore it you will need to possibly execute some IO 
POKE commands from basic to write some garbage to the nvram to corrupt 
it, then rerun the system disk.
If you have a ds12887a ONLY, you can cut off the /CLR pin or bend it 
sideways so it doesn't make contact with the socket (and presto, its now 
a ds12887)
I ran into this mess a few years ago.

Btw, only difference between ds12887(a) and ds1287(a) is the former 
supports y2k/century byte, the latter doesn't.

On 8/6/2016 10:39 PM, Stephen A Edwards via vcf-midatlantic wrote:
> Found an IBM PS/2 Model 60 (huge tower) a while ago. It powers on, displays
> video, complains about the CMOS memory, and refuses to boot further.
> I spent a day fighting with the 3.5" 1.44MB floppy: I recapped it, cleaned
> the heads, cleaned the track 0 sensor, and it's now happier than it used to
> be, but it still won't boot disks (it seeks to track 0 on reset, and spins
> the disk for a bit when it's trying to read track 0 for boot, but then
> gives up shortly after that). It's a strange floppy: a 40-pin edge card
> connector instead of the usual 34-pin.
> It has a 5.25 MFM (?) drive in it (90X8643 MCA controller card) that spins
> up and seems to move heads around, but it doesn't seem to want to boot off
> of that either, perhaps because the CMOS information is gone. Anybody
> familiar with how that needs to work.
> So I'm looking for advice, or reason to get rid of it. Anybody have a spare
> 3.5" floppy drive FOR AN IBM PS/2 kicking around (i.e., 40-pin edge card
> connector)? Is there any way to fix up the CMOS memory without booting a
> floppy? (It doesn't seem to have BASIC) Anybody have a MCA SCSI controller?
> Or does anybody want to take this boat anchor off my hands?
> -Stephen

Jonathan Gevaryahu
jgevaryahu at gmail.com
jgevaryahu at hotmail.com

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