1541C unusual "Shorter Board" version - J3?

Disk drives, Monitors, SuperCPU etc.
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Gyro Gearloose
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Re: 1541C unusual "Shorter Board" version - J3?

Post by Gyro Gearloose »

It's not enough for the head to be similar, it needs to fit both the rails and the metal band for the stepper motor. Also the erase method needs to be the same, the 1541 uses straddle erase heads, most other mechanisms use tunnel erase. This means the more you write to the disk the more timing errors accumulate in the guard bands. It probably won't matter if you just copy files over once but if you actually read and write to the disk it's going to be a problem. You actually need the controller to accommodate these different erase methods. The good news is that's not complicated and the DOS doesn't need to know about it, but you do need to do some hardware mods.

What little I've found out about 5.25" mechanisms shows me that there were several standards for the rail spacing and the stepper attachment. And that the single-sided mechanisms are different enough from double-sided so that you can't just swap heads.

You can find some technical info from drive datasheets. The most amazing mechanism I've seen is the Mitsubishi M4851.

http://www.primrosebank.net/computers/b ... _M4851.pdf

Here's the TEAC info, I think that's the drive that uses the head I linked to earlier.

https://nfggames.com/X68000/Documentati ... enance.pdf

This is more for being amazed at how serious floppy drives once were ... 200 pages of information ... to *repair* a mechanism.

Anyhow here's a more in-depth look at the nitty-gritty of getting 1s and 0s on a flimsy plastic circle with some magnetic coating ...

https://archive.org/details/bitsavers_m ... ms_1029819


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Re: 1541C unusual "Shorter Board" version - J3?

Post by rmzalbar »

Gyro Gearloose wrote: Sun Nov 06, 2022 5:15 am ..Also the erase method needs to be the same, the 1541 uses straddle erase heads, most other mechanisms use tunnel erase. This means the more you write to the disk the more timing errors accumulate in the guard bands. It probably won't matter if you just copy files over once but if you actually read and write to the disk it's going to be a problem...
Yep. I sometimes use 96tpi drives to remaster commodore disks from images (I have a Supercard Pro and a Kryoflux) and this works fine. However, you have to degauss the disk before you do that, because the 96tpi drive won't do a wide enough erase and the 1541 head can see the garbage to either side.
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Re: 1541C unusual "Shorter Board" version - J3?

Post by banman »

Hi Gyro Gearloose and rmzalbar,

Very interesting.

I was unaware of the Supercard Pro and a Kryoflux card.

Am I correct in thinking these cards will plug into say any type of 5.25" or 3.5" physical drive to extract the contents of a floppy disk assuming they meet the dimensional requirements of a particular drive?
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Re: 1541C unusual "Shorter Board" version - J3?

Post by Gyro Gearloose »

I don't know, don't own either, but the site for the Kryoflux says

"Shugart (with extensions) drive interface; 34-pin dual-row header connector
supports 3.5" and 5.25" floppy drives, also works well with selected 3" (e.g. Amstrad FDI-1) and 8" (e.g. Shugart 851; might require additional adapter) drives; other types of drives and media currently under investigation"

"It is unlikely but possible that certain models of floppy drives may not work with the board. We can't accept returns for a board not working with a particular drive when it does work with other ones that are compatible."
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Re: 1541C unusual "Shorter Board" version - J3?

Post by rmzalbar »

They're a go-between from a PC USB to a drive that uses 34-pin Shugart. 3.5" and 5.25" for sure, 8" should also work with an adapter. They have onboard logic to buffer tracks and provide flux data to the host PC.

They're primarily used to make accurate disk images for archival purposes from 70s-90s era disks, preserving even copy protection schemes. They can also be used to remaster same with close to 100% success with respect to said schemes.

The two cards and supporting software differ somewhat in their design goals and capabilities. Getting data off the backside of single-sided disks such as produced by Commodore/Atari/Apple machines ("flippy disks") can only be done on the Kryoflux by mechanically modifying a double-sided drive to handle the head offset. The Supercard can ignore the index sensor so you can read them by simply flipping the disk over.

Kryoflux software and ecosystem tends toward decoding the flux to verify valid data against existing archives and encoding schemes. The organization backing Kryoflux is primarily focused on C64 support. Supercard attempts no validation of the raw flux, it's up to you to process it further with other software such as HxC though you could simply write it back to a new disk to create a direct clone of the original. There's a number of community-provided utilities that support either of these cards for various systems. There's a 3rd device called Catweasel from good old Individual Computers that I don't know much about but provides similar capabilities. There's a 4th, open-source interface card called Greaseweazle that has similar capabilities to these three commercial options, I don't have this one either.

One thing that should be made clear is that writing disks, although supported, is not the focus of the archival-oriented backers of these projects so the tools are not as mature in this regard, generally speaking. It tends to be my primary use of it though.

There's definitely a bit of juggling between various PC floppy disk drives for their capabilities. Mainly, 96tpi vs 48tpi (96 would be mandatory if the original software used half-tracks for example) and little niggles you have to keep straight such as if the drive has a hardwired requirement for an index pulse or not (so you can flip the disk..) and whether or not you can just erase a floppy or if you'll need to degauss it, etc.

If you're looking for something new to do, it's certainly a headache that will keep you busy for a while.
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Re: 1541C unusual "Shorter Board" version - J3?

Post by Gyro Gearloose »

Rereading this thread, I have a question: where does one find 12$ 1541s these days? Super-duper patience on eBay?
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Re: 1541C unusual "Shorter Board" version - J3?

Post by banman »

Hi Gyro Gearloose and rmzalbar,


A $12 1541 is a good price! I have bought very cheap things on eBay and Gumtree in the past.

As rmzalbar has suggested there's a large amount of sellers advertising at exorbitant prices on places like eBay. Maybe even ghost bidders pushing the prices further than they might ordinarily be.

It tends to appear more often than not when searching these on-line selling sites. Maybe eBay encourages these higher priced items, maybe eBay gets a bigger sale royalty, I'm not sure. It would be very interesting to pursue.

I have over time picked up various very cheap things on eBay. Watching and waiting for an item has been a good strategy for me. However it can be a very tedious process.

I did pick up a very nice C64C a few years ago on Gumtree (like Craigslist) at a ridiculously low price.
It was by chance the advert had posted almost at the same time I was looking at the site (I would say minutes). I immediately responded to the advert and both I and the seller agreed to the sale. This closes advert so it doesn't appear on the site as being on offer. I imagine that one might be able to do a sold history search to see these transactions.

Does eBay listings operate this way too?

It is absolutely necessary to get to know the product you're interested in and it's "real" price. It is so easy to get caught up in the bidding game.

I always like to ask myself, so I need it or do I want it. This helps me not to go over the top when casting a bid.
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Re: 1541C unusual "Shorter Board" version - J3?

Post by banman »

Very quick update...


I just got delivered today a Blue Chip BCD/5.25 Disk Drive less any cables or power supply.



I paid $70AUD shipping not included.

I understand from reading this article https://www.pagetable.com/?p=1306
that one commenter suggested that a SpecraVideo 318/328 power supply might be compatible.

As luck would have it I happen to have 2 of these power supplies. I got them in a box of junk from the electronic store that closed down.
IMG_20221112_143815.jpg
IMG_20221112_143847.jpg
IMG_20221112_143727.jpg
The power cable even looks the same and has similar numbers stamped on the plug and receptical.

I'll make double sure that it's suitable before trying it out on this Blue Chip BCD/5.25 Disk Drive .
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Re: 1541C unusual "Shorter Board" version - J3?

Post by banman »

As one can see this drive has signs of yellowing. Looks like the catch had been left on the down position for a very long time.
I don't know much about this unit.
Maybe someone can tell if this drive is 1571 compatible or if it's a 1541 drive?
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Re: 1541C unusual "Shorter Board" version - J3?

Post by Gyro Gearloose »

This is a 1541 clone. I don't know much about it, it doesn't seem to use a Newtronics mechanism so you don't have to worry too much about failing heads.

It also appears to have a higher build quality than another 1541 clone, the OC-118/Excelerator which is unreliable.
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