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Booting a restored XT - BASF 6129 floppy drive

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First post, by tolstiakov

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Hi folks, my first post here. Been reading this forum for a while, so it's about time to join. I restore all kinds of vintage electronics, from TVs and radios to lab instruments and computer hardware. Given the limited free time for this hobby I try to keep my item collection small, but have everything in working order if possible. Over time I accumulated a handful of AT and some XT boards, MFM/RLL disks and controllers, and the associated cards from that era. I've been low on storage space at the time when cases for these were much more abundant than today, so unfortunately I ended up with much more boards than cases to install them into.

I recently acquired a mint condition PC-XT clone (case only, no monitor) with one of those generic Turbo-XT 8088 IBM clone boards with 640kB RAM. NiCd battery had leaked (on the IO/RTC board), but fortunately the damage was minor and easy to repair. Unlike AT and newer stuff, I have very little experience booting XTs. It has two 20MB HDDs and one floppy drive - the BASF 6129. I had to refresh the grease on the head slider mechanism, and also cleaned the heads. I tried to make it boot by formatting a 2S/HD floppy disk in a 1.2MB drive (using the magnet wipe method, 'format a: /4' command, and sys-ed it with DOS 6.22). It did not work, the drive spins but does not read.

Next I attached the BASF drive to a working 286 (setup as 360k drive in BIOS) running DOS 6.22. My attempt to format a known good 2S/HD disk resulted in a 180kB size formatted disk (??) with some bad sectors. Forcing the format size with /f:360 sometimes results in "Invalid media or track 0 bad" or again in a 180kB filesystem. Files can be written to the disk, but reading is intermittent. So my questions are:

  • I've been unable to find any documentation for the BASF 6129 drive online, apart from the two pics attached. It's made in Japan, likely a rebranded model. Can anyone recognize it?
  • I hope I won't need to use the 48tpi disks with this drive, right? I have none, and instead a handful of good 2s/HD 96tpi disks. Any general advice on this and the above described drive behavior?
  • Is DOS 6.22 an overkill for an XT? I'd be glad if there are some downloadable 360kB images out there optimized for the XT, to save some effort.

Thanks in advance.

Reply 1 of 3, by jakethompson1

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I've used that trick successfully but with 1.44MB and 720K by taping over the hole. It was bootable/readable on an XT clone even though the BIOS doesn't have support for 3.5" disks. Something about the floppy disk parameter table only being used for formatting (which won't work) and the FAT being instead used when only reading a disk, so 720K works (but 1.44MB doesn't). With 5.25" disks, the magnetic differences between a 360K and 1.2MB disk are much greater I believe, so I'm not sure what you're trying will work out for you.

Reply 2 of 3, by Horun

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If the 6129 is like the 6128 then this may help: https://www.retrocmp.de/fdd/basf/6128/basf-6128c.htm
Yes formatting a 1.2mb floppy to 360k in a 1.2Mb drive rarely works in a 360k drive, formatting a 1.2Mb disk in a 360k drive usually works if the media is good.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 3 of 3, by tolstiakov

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Success, I managed to boot the XT. Primary hard disk (BASF 6188-R3) is not readable any more, however the secondary (Seagate ST225) is fully readable with only a few weak sectors near the end. Last timestamps on files are from 1992.

jakethompson1 wrote on 2022-08-18, 20:28:

With 5.25" disks, the magnetic differences between a 360K and 1.2MB disk are much greater I believe, so I'm not sure what you're trying will work out for you.

You're right, apparently this BASF 6129 drive really hates HD media. No matter what I do it spits disks out with "Invalid media or track 0 bad...", or creates a weird sized filesystem with lots of bad sectors. Luckily I found a few DD disks in my pile, I was able to format these correctly as 2S DD 360k disks on another AT machine. Moving the drive to the XT I booted DOS 6.22 on it. Interestingly, probing the signal with the oscilloscope is not in correlation with the practical result. The HD media signal looks stronger and better articulated compared to the DD, but the drive does not play with it. There are two trimmers on the PCB, but with no documentation I have no idea what they do. One other thing, the chassis of the drive needs to be grounded if operated outside of the case. An alligator clip wire is sufficient. Otherwise the drive picks up random interference and may misbehave.

Horun wrote on 2022-08-18, 20:41:

If the 6129 is like the 6128 then this may help: https://www.retrocmp.de/fdd/basf/6128/basf-6128c.htm
Yes formatting a 1.2mb floppy to 360k in a 1.2Mb drive rarely works in a 360k drive, formatting a 1.2Mb disk in a 360k drive usually works if the media is good.

6129 is quite different (see pics from the first post). I'm still amazed that no documentation can be found, hope somebody proves me wrong...

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