[rescue] Anybody remember MFM? (Durango Poppy II problem)

Curtis H. Wilbar Jr. rescue at hawkmountain.net
Tue Aug 5 22:19:34 CDT 2003

>From: Walter Belgers <walter+rescue at belgers.com>

>Mike Hebel wrote:
>> > Now the problem: although the Micropolis 1325 71MB MFM drive spins up, 
>> > I
>> > cannot read/write it, I get an error on the first block. I do have the
>> > correct /dev entry: the HD drive LED goes on. I tried inserting another
>> > (21MB) MFM drive with the same problem.
>> Inserting another drive probably won't work.  You might want to look at 
>> some low-level formatting routines.  Some of the older cards you had to 
>> use a command in DOS debug to get to the low-level routines:  c800:g    
>> Depends entirely on the card.
>The 21MB disc was DOS-formatted (with MS-DOS installed, I took it out of
>a 80286). So I don't think low-level formatting would help (besides,
>since I cannot boot DOS, also not from floppy, I have no way to perform
>a low-level format). The system has no interactive BIOS AFAIK.

MFM (and RLL) formatting was not standardized across controllers.  Format
your drive on a WD controller, and move it to blah controller and it
won't work... you need to low level format to match the controller.

In this case you need to find out how low level formatting is supposed to
be performed.

It sounds like the system has a bridge controller... either SASI or SCSI
to MFM.  Is there any information on the bridge controller.  Adaptec
made a SCSI->MFM bridge (Sun used these in Sun-2 and early Sun-3).
Emulex may have also made one.  Xebec made a SASI->MFM bridge.

Low level formatting is probably done through some utility, possibly
booted off of a diagnostic disc, or since this is PC based, in a BIOS
on the controller card.  This would be accessed via booting dos, going
into debug, and executing g=dc00:5 or something like that (I think that
address works for one of my ESDI cards... or was it c800:5 ??? been
a long time).

>> > The drive is connected to a board from 'Molecular Systems' which has 3
>> > connectors: 2 for the MFM drive and a 50 pin connector. I am hesitant 
>> > to
>> > try out if it's SCSI. Were combined MFM/SCSI cards normal in the old
>> > days?
>> Umm...not that I can recall but it _might_ be SCSI-1.  If it is you'll 
>> probably not find a drive that will run on that connector.
>Why not? SCSI-2 drives should work on a SCSI-1 controller?

If it is SCSI... it could be SASI.

>> > Also, there are two potentiometers (is that English? variable 
>> > resistors)
>> > that are next to the MFM connectors. Would fiddling with those improve
>> > my chances of getting this thing to work?
>> Don't mess with those!  If you're having a problem _now_ then you could 
>> very well put yourself totally out of the picture because you'll never 
>> get them back into the original adjustment.  IIRC they had something to 
>> do with sync.  Data or motor I can't recall but either way they aren't 
>> easily adjusted properly without the original signal specs from the 
>> board manufacturer.

I echo this... don't "adjust" anything unless you know what it is and
have the equipment for the procedure (along with the procedure :-) ).

>Then again, these may cause the problem..
>Walter Belgers         "Si hoc signum legere potes, operis boni in rebus
>walter at belgers.com       Latinis alacribus et fructuosis potiri potes!" 
>rescue list - http://www.sunhelp.org/mailman/listinfo/rescue

-- Curt

Curtis Wilbar
Hawk Mountain Networks
rescue at hawkmountain.net

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