Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site cvl.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!cvl!hsu
From: hsu@cvl.UUCP (Dave Hsu)
Newsgroups: net.micro.apple
Subject: Re: Re: Banging noise on Apple //e,c disk dr
Message-ID: <426@cvl.UUCP>
Date: Sat, 11-May-85 01:53:43 EDT
Article-I.D.: cvl.426
Posted: Sat May 11 01:53:43 1985
Date-Received: Mon, 13-May-85 00:12:08 EDT
References: <573@spp2.UUCP> <4400001@hpvcla.UUCP>
Organization: Computer Vision Lab, U. of Maryland, College Park
Lines: 29

> 
> 	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