24 Apr
2011
24 Apr
'11
4:56 a.m.
Eric writes:
Fred Cisin wrote:
Most of my suffering with MFM drives happened at the upper end of
the cost/complexity spectrum.
Looking back 20 years I in fact have good respect for the simpler of
the MFM drives and the ST-225 is an example.
Maybe my expectations were just lower for a drive that didn't cost
$4000 (list price of a XT-2190). But it's also quite true that ST-225's
didn't crap out at the rate as the much more expensive MFM drives
and for that I have to really give them some credit.
Tim.
"trusty ST-225"??
Well, as
compared to some brands, yes. JTS comes to mind, though it
wasn't contemporary with the ST-225. 
24 Apr
24 Apr
7 a.m.
On 4/24/11 7:56 AM, Shoppa, Tim wrote:
Eric writes:
I always had very good luck with ST-225s. I ran one or two at home,
and installed lots of them in customer machines.
One important thing for ST-225s and ST-251s is to not tighten the
screws at all four corners. After many unexplained high-error-rate
installations, we determined that the drive's metal substrate twists
slightly due to thermal expansion when the drive heats up, throwing off
the head/track alignment. These drives don't use any sort of
servo-positioning scheme to maintain head/track alignment; they use a
stepper motor arrangement similar to that of many floppy drives, so any
mechanical drifting doesn't get corrected. Leaving two
diagonally-opposed screws loose solved the problem in every case.
-Dave
--
Dave McGuire
Port Charlotte, FL
Fred Cisin wrote:
Most of my suffering with MFM drives happened at the upper end of
the cost/complexity spectrum.
Looking back 20 years I in fact have good respect for the simpler of
the MFM drives and the ST-225 is an example.
Maybe my expectations were just lower for a drive that didn't cost
$4000 (list price of a XT-2190). But it's also quite true that ST-225's
didn't crap out at the rate as the much more expensive MFM drives
and for that I have to really give them some credit. "trusty ST-225"??
Well, as
compared to some brands, yes. JTS comes to mind, though it
wasn't contemporary with the ST-225. 
7:33 a.m.
On Sun, 24 Apr 2011 10:00:49 -0400, Dave McGuire wrote:
One important thing for ST-225s and ST-251s is to
not tighten the
screws at all four corners. After many unexplained high-error-rate
installations, we determined that the drive's metal substrate twists
slightly due to thermal expansion when the drive heats up, throwing off
the head/track alignment. These drives don't use any sort of
servo-positioning scheme to maintain head/track alignment; they use a
stepper motor arrangement similar to that of many floppy drives, so any
mechanical drifting doesn't get corrected. Leaving two
diagonally-opposed screws loose solved the problem in every case.
I remember one system, came in having drive problems, when I loosened the screws on the
drive, there was a
distinct noise as the case tension was relieved.
After the stress was relieved the drive tested ok, and went on to work just fine for many
years.
Well that is after tweeking the case back closer to square and remouning the drive at
cross corners.
It looked like the drive was tight in a twisted cage, in a case that was twisted back so
the cover would fit better.
The other Bob
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caveguy＠sbcglobal.net -
mcguire＠neurotica.com -
tshoppa＠wmata.com