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Backpack 5 1/4 Floppy : 360KB on 1.2MB / TEAC 55-GFR

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RetroHospital

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Thanks to help from @Chuck(G) and the invaluable @modem7 website - I was able to make a 5 1/4 Backpack work again on the parallel port of a Toshiba 2130 (486 era laptop) running msdos 6.22

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The documentation of the backpack (the flyer) says this drive should be able to both read & write 360KB floppies
Internally this is a TEAC FD 55GFR, together with a floppy driver and power supply.

I've installed the oldest drivers under dos. The drive works great (read:format) on 1.2Mb floppies

However I've got a "cylinder 0 unreadable" or "unusable" error both with BPFORMAT /360, or plain MSDOS format /4 or format /f:360
I don't seem to be able to read 360K floppies either. This is a bummer, I had hopes this would read everything and be my cross generations dream system.

The fact there is an option to create 320, 360, and even 720K 5/14 floppies in the backpack software menues also suggests this should work !?

Any help appreciated !!! ; this might well be a pure msdos/driver problem, I'm new to making 360KB floppies work, and I realize I'm not in the easiest scenario (1.2MB floppy on a parallel interface with drivers nobody has seen or seriously used since 1994 )
 
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Reading the 360K floppies should work. Do you know if the disks were created on a 1.2 MB drive? Are the disks decaying? Do they have 360K PC formats? Alignment issues or damaged disks are what comes to mind with repeated failures. Copy protection or non-standard formats may cause issues.

FORMAT /4 /u may push past track 0 issues. Sometimes, degaussing the disk can help.
 
One possibility would be that the former owner, who claims to have used the teac drive inside greazeweazle (so took the backpack apart to use only the drive) tuned the jumpers. It is unlikely - but not impossible.

Currently the jumper "I" (auto detect) is set to a constant 360rpm speed. It is unclear to me even after MUCH reading if I can read a 360KB floppy with the jumper "I" to OFF (which means speed set to 360rpm all the time).
Can HD drive read 360KB floppies at 360rpm ? I understand that a change in bitrate can compensate the higher speed, the question remains how does auto detection work then ? What happens in I put a 360KB floppy inside a 55GFR with speed set at constant 360rpm ? Does it like "switch between bitrates looking for valid DD data" ? If so, I really wonder what use there is for the "auto speed" jumper at all...
 
I got errors even with brand new nos verbatim disks ; both read and write ; always cylinder 0 thing
I can’t read or format

The drive basically ignores these are ds/dd floppies and even formats them as HD if I don’t force it otherwise .

By the way I’ll post pictures of the inside of the backpack for the future generations .
 
CedsRepairs said:
One possibility would be that the former owner, who claims to have used the teac drive inside greazeweazle (so took the backpack apart to use only the drive) tuned the jumpers. It is unlikely - but not impossible.

Currently the jumper "I" (auto detect) is set to a constant 360rpm speed. It is unclear to me even after MUCH reading if I can read a 360KB floppy with the jumper "I" to OFF (which means speed set to 360rpm all the time).
Can HD drive read 360KB floppies at 360rpm ? I understand that a change in bitrate can compensate the higher speed, the question remains how does auto detection work then ? What happens in I put a 360KB floppy inside a 55GFR with speed set at constant 360rpm ? Does it like "switch between bitrates looking for valid DD data" ? If so, I really wonder what use there is for the "auto speed" jumper at all...
Click to expand...
The controller in an IBM AT has the 300 kbps mode to read/write double density disks when running at 360 RPM. The drive spins 20% faster so the data is transferred 20% faster. I don't know the inner working of the Backpack well enough to know if they used that method or if the drive was forced to a slower speed to handle double density 5.25" disks. None of the technical support notes that remain on the archived Micro Solutions website mention issues for the 5.25" high density Backpack dealing with double density disks.

This is all very strange.
 
krebizfan said:
The controller in an IBM AT has the 300 kbps mode to read/write double density disks when running at 360 RPM. The drive spins 20% faster so the data is transferred 20% faster. I don't know the inner working of the Backpack well enough to know if they used that method or if the drive was forced to a slower speed to handle double density 5.25" disks. None of the technical support notes that remain on the archived Micro Solutions website mention issues for the 5.25" high density Backpack dealing with double density disks.
Click to expand...
I've posted before on this one (a few times). The BP contains a NSC DP8473 FDC Datasheet here with an 8051-style MCU and a small SRAM and a very small EEPROM. Other than passing commands over the parallel (nibble mode) interface rather than the ISA bus, it's the same as any other floppy controller and is certainly capable of 250/300/500 bps operation. At one time, I even posted code (reverse engineered) on how the interface operates. You send commands to the controller, basically. Nothing fancy.
In point of fact, other than the limitations imposed by the power supply and enclosure, the BP is perfectly capable of supporting 4 drives, with the drive types set in the NVRAM. It might be a good idea to verify that this hasn't be bollixed by running the SETID DRIVETYPE command.
 
DRIVETYPE just asks you if it is a 360 or 1.2MB drive, i've set it again to 1.2 but that didn't change a thing, but it was worth a try

Under windows 95 (with the bp drivers) same thing ; can format 1.2M, can"t format or read 360K. Mhhzzzz

At this stage I see 3 possiblities
- the floppy is broken (misaligned ?)
- there is an incompatibility with my toshiba
- the TEAC 55GFR has jumpers that are not stock to a backpack ( especially the autodetect one that is "off" )
 
What is super odd also is that this "cylinder 0" error (reported by both msdos format and the Bp's own format tool) is nowhere to be seen on the internet, except in the amiga world.
 
Yes, I tried formatting disks that I knew were already PC formatted, and also tried formatting new old stock (cello) PC DS/DD medias.

I really feel I'm missing something obvious, I wish I had more experience.
Maybe switching PC will shed some light on this. If I've got the same problem on a competely unrelated Compaq SLT386 under dos 3.3, I know that the problem is in the unit.
 
At this stage I've tried everything, all things point out to : the backpack -at least the one I've got, the all metal one similar to the Tandy external drive (made by the same company) simply cannot write or format 360KB disks.
Even if the backpack software (backfmt/bpformat) has an option for that. I always end up with a cylinder 0 error.
If you search the web deep enough, there is one bit of documentation saying the backpack can "read" 360KB disks but doesn't talk about writing. There is another bit of documentation that says the opposite. Maybe only a specific model of backpack (or driver ?) is able to do both, as clearly the 5 1/4 backpack existed in all metal (which I've got) and also full plastic (which I don't have).

It's also unclear of the teac FD55GFR can write 360KB disks. My understanding of the documentation is that the "R" for "revised" "drop supports of DD formats", whatever that means, so did they drop writing, reading, or both - not sure.
If anybody has a Teac FD55GFR (which is rather common), or knows about it, and could confirms the thing - on another controller like directly connected on a PC or a greaseweazle, can write/format 360KB, this could also help my investigations...
 
https://archive.org/download/Teac_F..._Teac/Teac_FD55GFR_Floppy_Drive_1996_Teac.pdf is the manual. Double check the jumpers. The manual shows that track 00 errors occur when double density formats are applied to high density disks.

If you can, use the floppy drive with a standard high density floppy controller. That would narrow the problem to either drive or to the Backpack enclosure. The drive on its own should format and write to 360K. An actual 360K drive may not be able to read the result.

I suspect that somehow pin 2 (density select) isn't changing value when double density formats are chosen. Maybe the cable got damaged.

The Portable Paper review of the Backpack does indicate that version of the 1.2 MB drive could format 360K disks.
 
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