Greaseweazle -- uniform odd/even read errors on 360 KB disks

[SummanusPachamama]

Hi all—I've seen an awful lot of Greaseweazle threads on this forum so hope this is the right spot. I've got a cache of IBM floppies from a family friend who was an amateur radio operator, and some appear to have specific software written to help hams operate their "packet" protocol (among other specialized applications). I've even got some C64 disks mixed in. Some of this does not appear to be archived on the Internet, so I'm hoping to use my Greaseweazle + TEAC FD-55GFR to salvage what I can and get it on the Wayback machine and circulate it in the ham radio community. Unfortunately, this cache sat in their garage for the last 30 years, where it was subject to midwest temperature changes, so I'm not positive my problems below aren't simply the result of wholesale corruption of the media.

I can handle 1.2 MB HD disks, no problem. The drive flies through them with no bad sectors (test drove some early 90s Microsoft install disks; Excel & Microsoft Mouse). But for 5 separate 360 KB diskettes I've thrown at it, I'm getting the exact same pattern of errors, which I also get on a my spare HP 0950-1974 drive:

1. Track 0 reads fine.
2. Tracks 1, 3, 5, and so on through 39 all give missing sector errors (0/9).
3. Tracks 2, 4, 6 and so on through 38 all give unexpected sector errors (discarding the read).

I suspect this has to be something to do with DD vs. HD disk formats—it feels like it's trying to read half-width tracks in a full-width space, so the parameters return invalid data for the first half-width section, after which the the second read finds full-width data midstreams and ignores it as unexpected. But I am sadly just not experienced or literate enough with floppy details to really know how to attack it from this point. I'm getting the same pattern whether I use SCP/no specified format, or IMD with IBM 360 KB format. I've read that the TEAC could spin at 360 rpm, so I've also checked the "Adjust-Speed" option to 300 on these smaller diskettes, but it's making no difference. I'll attach my parameters in the Greaseweazle GUI + how they look in HxC.

I appreciate any assistance and apologize for what must be something extremely elementary.

 

[SomeGuy]

Don't dump directly to an ImageDisk format. Dump directly to a flux format (I believe that outputs SCP format).

Display that in HxC and it will give you a much better idea of what is going on. (It also captures copy protection, and may get the best possible read if a disk if falling apart).

When dumping a 360k disk in a 1.2mb drive you have to either make sure the drive is "double stepping", or tell the decoding software afterwards to ignore the odd tracks.

BTW, looking at the flux image in HxC will show you the track and sector ID in each sector it finds, so you can tell if the head is over the wrong track.

 

[SummanusPachamama]

Thanks a ton. That perfectly dialed it in. Probably some redundant parameters but I rolled with gw.exe read --format=scp --adjust-speed=300 --tracks=step=2:c=0-39:h=0-1 --device=COM4 "D:\\Test.scp" and it smashed through it perfectly, all 720 sectors recovered on my first disk. Time to get to work.

I really want to preserve these floppies that are still working with zero bad sectors; it's a miracle they survived this long in that garage. I've heard the rumors about SpinRite 6 being able to "refresh" the charge but who knows.

 

[SomeGuy]

Do NOT use anything that writes back to the disk. That will almost always make things worse, and will invalidate authenticity on factory made disks. Those tools were not designed for disks that were shedding oxide or covered in "mold".

For recovery these days the options are really either a flux reader, and/or a tool like disk2img that rapidly reads and retries sectors on real hardware.