Reviving ancient MFM drives (was Re: formatting MFM drives on a IBM PC)

Tom Gardner t.gardner at
Fri Sep 29 00:36:48 CDT 2017

Old 10 and 20 MB  MFM drives are most likely open loop positioning systems which are highly vulnerable to off track due to thermal changes and stiction.  They also could have flying height problems due to contamination on the slider.  These failure modes can manifest themselves a slow soft problems such as you are describing

One thing I would do is format them only after they are warmed up and well exercised and then I would never turn them off.  If I did turn them off then I would have a batch file do a bunch of seeks for a minute or so during the boot and if I were really clever find a way to do a seek  every 5 minutes or so.


-----Original Message-----
From: Adrian Stoness [mailto:tdk.knight at] 
Sent: Thursday, September 28, 2017 9:41 AM
To: Geoffrey Oltmans; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Reviving ancient MFM drives (was Re: formatting MFM drives on a IBM PC)

prolly a failing ic of some sort?

On Thu, Sep 28, 2017 at 11:21 AM, Geoffrey Oltmans via cctalk < cctalk at> wrote:

> On Thu, Sep 28, 2017 at 11:17 AM, Al Kossow via cctalk < 
> cctalk at> wrote:
> >
> >
> > On 9/28/17 7:38 AM, Mike Stein via cctalk wrote:
> >
> > > What is it that usually fails when the drive can't read the servo info?
> > The data on the platter, or?
> >
> > I've never dug that far into it beyond fiddling with Micropolis 
> > trying to mechanically get it to find the servo tracks and calibrate 
> > to track 0.
> >
> > One of the problems is schematics and documentation on the servo 
> > systems are extremely difficult to get. The little that is on 
> > bitsavers is all I've come up with in 25 years of searching and 
> > there is practically nothing useful elsewhere on the web about 
> > fixing servos in old 5" disks.
> >
> > It could be heads, media, positioners, component aging in the analog 
> > section, etc etc..
> >
> >
> >
> >
> Speaking of.... I've got a couple of old MFM drives (10 and 20 MB of a 
> variety whose name and model #'s escape me, I wanna say Tandon, but 
> not sure). They seem to work fine when I initially format and 
> partition, but as they run for a while, they get more and more 
> unreliable. It seems to be a function of how long they've been running 
> for rather than a predictable pattern of bad tracks sectors? Are there 
> any good sources of troubleshooting info at the controller level for these old drives?

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