e,c disk dr

davel@hpvcla.UUCP (davel) (05/08/85)

	When DOS has trouble reading a diskette after a few
	tries it "re-syncs" the head. It does this by pulling
	the head up against a mechanical stop. Because the
	head motion is an open loop control system (etc.) it
	hits the stop several times causing the banging. The 
	underlying cause is that the head alignment is 
	different on the drive that made the Beagle Bros. disk
	and your disk.

				Dave Lowe
				hpvcla!davel

hsu@cvl.UUCP (Dave Hsu) (05/11/85)

> 
> 	When DOS has trouble reading a diskette after a few
> 	tries it "re-syncs" the head. It does this by pulling
> 	the head up against a mechanical stop. Because the
> 	head motion is an open loop control system (etc.) it
> 	hits the stop several times causing the banging. The 
> 	underlying cause is that the head alignment is 
> 	different on the drive that made the Beagle Bros. disk
> 	and your disk.
> 
> 				Dave Lowe

Noticing the //e in the top...is this unit equipped with a Duodisk?
Or did you buy the single disks?  It seems that the newer mechanisms
do occasionally need to be realigned, while the older ones with the
Shugart guts had a reputation for never needing service aside from an
occasional speed-calibration and head cleaning.

Just a small(?) note: the Apple is not "re-syncing" the drive.  It is trying
to restore track position.  Most micros do this, but some do not do a very
good job of it.  Commodore 1540 and 1541 drives are notorious for losing
alignment because their stops are adjustable, and the setscrews come lose
after a few minutes of use due to heat build-up in the under-ventilated
cases.  Running the original copy program on protected disks and leaving
to grab some food caused many machines to be returned for service at the
computer store I used to work at.  Re-syncing is accomplished by waiting
until the drive reads a self-sync byte, no more than a long string of ones.

-dave

zben@umd5.UUCP (05/12/85)

I beg to differ with you, Dave, but "resynching" is what this is called,
throughout the microcomputer world.  The usage is universal.  

Regardless of whether it is meaningless or confusing, thats the term in
general use.  Most people can just about handle tracks and physical head
motion, but don't understand *record* resyncing, so the conflict does not
arise in practice.

I could probably use more of this advice than you, but for what its worth,
you shouldn't criticize until you understand...
-- 
Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA

davel@hpvcla.UUCP (davel) (05/14/85)

>Noticing the //e in the top...is this unit equipped with a Duodisk?
>Or did you buy the single disks?  It seems that the newer mechanisms
>do occasionally need to be realigned, while the older ones with the
>Shugart guts had a reputation for never needing service aside from an
>occasional speed-calibration and head cleaning.

	I have had "banging" with one of my 8 year old single drives.
	In my case the symptom is slightly different in that it occurs
	only after the drive has set idle for some time (overnite).
	My guess is that the head somehow "settles" to an off track
	position. Does anyone know if DOS keeps the coils on the head
	stepper motor energized all the time (while the computer is on
	at least)?

	Dave Lowe

	P.S. I don't have a //e, I have a ][ that has had EPROM brain
	surgery to make it a ][+.