Date   : Sun, 13 Mar 1988 12:08:56 EST
From   : Paul.Birkel@K.GP.CS.CMU.EDU
Subject: SB180 help?

My apologies if this problem has been addressed in the past 6 or so months
that I've been off the INFO-CPM list.

I'm considering the purchase of a used Micromint SB180 configured with a
pair of DSDD 96tpi 5 1/4" drives. It's running a custom ZCPR3 from ECHELON.
Boots and runs fine off of a set of 96tpi disks. The problem is that it can
not read a disk formatted at 48tpi! This includes the original distribution
disks, and disks it has just formatted to 48tpi using the FVC (format, verify,
copy) utility. The same problem occurs when trying to read a disk in
KAYPRO II format (SSDD 48tpi), or using FVC to format such a disk. FVC is
perfectly happy in 96 tpi "mode".

In all such cases, I get a bad sector error, usually on track 1 sector 01
or something like 20. Booting from the distribution disks gives me the
system header message (like "ZCRP3 56k, etc") and then hangs. I do not
know if the ROM is producing this or not, but I would guess that it *is*
reading track 0 correctly since it is determining the system "size" correctly.
On the other hand, under some non-boot circumstances it fails on track 0
as well, so I'm not sure about this.

I thought that the problem may be that the system is trying to read the disks
in 96tpi mode, except that FVC when attempting to verify a disk formatted on
a KAYPRO II does produce a header correctly identifying the format, therefore
*must* be accessing the appropriate tracks. Just in case I changed the step
rate from 10 to both 6 and 20 ms. with no effect (except more noise in the
later case!!). I don't know of any other setable system parameters that might
affect this problem.

One could argue that the drive speeds have drifted leading to problems with
the distribution disks, but that does not explain identical behavior on either
drive, and the failure of FVC (which formats without complaint the appropriate
number of tracks and sides) to happily verify even a floppy it has just
formatted. One could argue that it's a write problem (on formatting), except
the distribution disks should be readable. If it were bit rot in the device
driver then I wouldn't expect *both* of two 96tpi system disks to exhibit the
same behavior.

The drives, I believe, are standard 55Bs (?). I have no documentation on
them. The SB180 docs describe jumpers which basically control things like
head load, motor control, and panel lights. The only board jumper has to do
with 8" vs. 5 1/4". So I don't think that there is a hradware configuration
problem.

As much as I otherwise like the system, I'm not purchasing it 'til I can
exchange data with it!! Unfortunately, the original owner died 3 years ago
and his brother is only now trying to sell it after gathering dust for the
duration. The brother is not especially technically knowledgable and just
wants to move it. I'm at a loss as to where the problem might lie. Help?

paul birkel

Dept. of Computer Science
Carnegie-Mellon University
Pittsburgh, PA. 15213

pab@k.cs.cmu.edu
(412) 268-8893