[Coco] Weird problem with Floppy drive

[Gene Heskett]

On Saturday 31 August 2013 18:38:00 Brian Goers did opine:

> Has anyone seen a problem like this?
> 
> I checked a dual floppy drive and under RSDOS I could DSKINI0, DSKINI1,
> copy a file drive 0 to 1 or 1 to 0, Backup both ways also. But under
> OS-9 I the drive 0 would not boot.
> I found the disk with *.bas and did a drive RPM test. Drive 0 was 296.4
> and Drive 1 301.3.
> 
> After adjusting dive 0 to 300.3 everything works fine.
> 
> So is RSDOS more tolerant of the disk speed?
>
Brian, I would not think that a 3.6 rpm (1.2%) error would be sufficient to 
bother it.  I once had a drive that turned 360, and in testing, I found the 
format (it failed on the first track) but the only reason it failed was 
that at 360 rpm, it had  turned enough at the end of the track write, that 
it over-wrote the beginning of the same track.  It was one of those 1.2 meg 
drives.  But I found the jumper that slowed it down to 300 and then it was 
fine.  I had by accident, bought a box of "QD" disks which purported of 
have a very hard magnetic coating, had an extra notch, and that was the 
only drive that wrote them strong enough to last,  any of my other 80 track 
drives would write a track that faded away in 20 minutes on those QD 
diskettes.

Slow by that amount (and I'd trust the strobe sticker on the bottom of the 
spindle a lot farther than any disk program) should be a total never mind.  
However, the early controller might get a bit funkity if the head is dirty 
& has low output, or is about finished/worn out, and its tuning pot needs a 
tweak.

I think that needs an oscilloscope to adjust that correctly, so says my 
common sense but check the manual, they may know a secret I don't remember 
since I have one, but its never been in the MPI to test.  I bought it in 
1990 or so thinking hi-density mod & then miss-laid my round tuit & haven't 
managed to find it again.

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