Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!pasteur!ames!lll-lcc!pyramid!cbmvax!fred
From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: 1581 error problems!
Keywords: Error #23!
Message-ID: <6609@cbmvax.UUCP>
Date: 18 Apr 89 12:40:41 GMT
References: <441@galen.acc.virginia.edu>
Reply-To: fred@cbmvax.UUCP (Fred Bowen)
Distribution: usa
Organization: Commodore Technology, West Chester, PA
Lines: 41

In article 441@galen.acc.virginia.edu> kws1x@dale.acc.Virginia.EDU writes:
>	While using the C= Assembler System, you know the one, I used the
>slash symbol to attempt to load a program from my 1581.  (This system allows
>you to load using "/filename".)  Anyway, the drive errored out.  Reading the
>error channel gave me error#23, a supposed checksum problem.  Dummy-me
>didn't have a backup of the disk I was accessing, and the same error pops
>up for half of the programs on the disk.  (I need these programs!!!)

This problem is fairly common to some (by no means all) 1581's.  Like the
SAVE-@ problems of earlier drives, the cause has proven elusive and it's not
certain that it's a software problem.  Miklos Garamszeghy wrote about this in
an article in Twin Cities 128 (issue #21), and included a program called '1581
Fix Track' which attempts to recover from these CRC errors.  I know the
program is available on QLink and GEnie, and probably elsewhere.  The program
takes advantage of the data in the track cache, writing it back to disk.  This
will eliminate the error, but cannot guarantee the validity of the data.  I
will see if Miklos has any objection to uploading the small BASIC program here
(the program is (C) Herne Data System, LTD.).

You should also check that your drive contains a WD1772 controller (not a
WD1770).  The replacement is still free I believe.  I posted a program to
report the controller type here not too long ago.

In article <487@jolnet.ORPK.IL.US> brendan@jolnet.ORPK.IL.US writes:
>  Get a copy of "Inside Commodore DOS" by Dick Immers & Gerald Neufeld..on
> page 469 of it, there is a program called "Recover Track & Sector"..you may
> have to change lines 420 and 530, due to possible differences in the zero
> page of the 1581 as compared to the '41  [...]

Methods other than Miklos' to recover the data by reading/writing the sector
given in the error message will often not work because the error could be
anywhere in the track and not necessarily at the specific sector indicated.
Also be careful using recovery programs written for other drives- the 1581
does not use GCR encoding, and the memory map is quite different!
--
-- 
Fred Bowen			uucp:	{uunet|rutgers|pyramid}!cbmvax!fred
				arpa:	cbmvax!fred@uunet.uu.net
				tele:	215 431-9100

Commodore Electronics, Ltd.,  1200 Wilson Drive,  West Chester,  PA,  19380