Probably the most sophisticated CP/M-80 machine ever made

[bw2341]

I haven't used floppies in a while, but I do follow a few retrocomputing YouTubers for entertainment.

One thing to watch out for is mould on the disk surface. It can cause the magnetic coating to flake off and contaminate the heads and other disks. If you see a white deposit that doesn't wipe off on the disk, you need to discard it.

The 720KB floppies are probably a rare 80 track format (called quad density?) using a media similar to 360KB DSDD floppies. The HD 1.2MB floppies are also 80 track but use 15 sectors instead of 9. They use a cobalt based formulation with a higher coercivity which is probably why they don't work in your drive.

Here's a huge webpage with more info:
https://www.retrotechnology.com/herbs_stuff/drive.html

The electrical interface of floppy drives are almost always the Shugart pinout so an emulator should work. Gotek seem to be an inexpensive design that has been repeatedly cloned by Chinese manufacturers. I also found a open project from a French developer with an official manufacturer and seller in Poland. They seem to have a large list of known working equipment including test instruments.

http://hxc2001.free.fr/floppy_drive_emulator/

[precaud]

Very interesting links, bw2341, thanks. I'll look into them.

Yes, these are "quad density" drives, but use double-density floppies. I remember that being a point of confusion (and uncertainty) back in the day. Mould is rarely an issue here in the desert southwest.

I found an almost-full box of brand new 2S2D floppies in a filing cabinet last night. This should be plenty for my needs.

[precaud]

Some random thoughts, and items of historical interest.

I was showing this to my son last night. He is a professional programmer with focus on UI, and was 3 when I bought the TEF10. Watching this work in a 64KB memory space elicited blank stares; "I don’t know of a single device I own that could run on even 100 times that much memory."

It's amazing what can be done in a 64k memory space if you set your mind(s) to it.

In use, there is a lot of disk activity, swapping program modules in and out. Really slows things down. This thing would benefit hugely from an SSD.

Some historical context: When the TEF10 was released, the IBM PC was already out and taking the world by storm. As you can imagine, Tecron took a lot of flack for coming out with a Z80 CP/M-based system, especially considering the price point. So why did they?
: You can't keep, or control, time accurately with an 8086/8088, because of the prefetch buffer (called pipelining back then); instructions don't always execute in exactly the same number of clock cycles. But you can with the Z80.
: Also, as I understand it, development of the system started in 1979, well before the PC was a "thing".

Not many TEF-10's still exist, because Tecron made a concerted effort to remove them from the market. They didn't want to (or couldn't guarantee being able to) service them. They did this by offering a generous tradein allowance to owners to upgrade to a TEF12, and later, TEF20. (I believe availability of the 720k floppy drives played a major part in this; they switched to the 1.2MB drives in the TEF12).

A note on serial numbers. The serial number on the back of the unit (22288) is not exclusive to this product. The only estimate I've heard is, they made around 175 TEF-10's. That number seems low to me. The only way to know, and to know where a particular unit falls in the sequence of release, is to look at the last digits of the CP/M license number, which were issued in order and written on the software distribution disks that came with the unit. This unit is #00007, one of the "pre-production" units offered.

[bw2341]

Via Adrian's Digital Basement, I found a collection of Shugart service manuals. I think the format of your drives would correspond to the SA465.

http://www.bitsavers.org/pdf/shugart/SA4xx/

As far as I can tell, the pinouts of 5.25 and 3.5 inch floppy drives are the same. The connector changed from PCB edge card to dual row 0.1 inch pin headers. If you want to connect a modern emulator to your floppy controller, you can even snap an IDC dual row connector directly onto your drive cable.

There are also non-permanent edge card to dual row adapters available. I found this from searching 3.5 to 5.25 floppy cable adapter:

https://www.ebay.com/itm/124055375980

Here's a PCB design to make one yourself:

https://www.pcbway.com/project/shareproject/5_25__Floppy_edge_connector_to_34_pin_3_5__floppy_drive_adapter.html

As you can see, the pins are connected straight through.

Even USB floppy drives use a Shugart interface internally. Here's Limor "Ladyada" Fried hacking a USB floppy drive via the Shugart interface and a link to a person who figured out the pinouts on the 1mm pitch flex cable connector.


https://jestineyong.com/examining-and-testing-a-small-universal-fdc-to-usb-adapter/

So for your test equipment, the first step would be figuring out if your drives have a standard Shugart interface and connector. If so, you can get an adapter to connect an emulator. The Gotek seems to have limited manufacturer support, but retrocomputing enthusiasts have hacked it with alternate firmware to support different formats. The HxC seems to have a discussion forum, so more direct support might be possible.

[precaud]

Dear bw2341,
You're making it very difficult to take the lazy route here    Thanks for your good sleuthing   
I hauled out the schematics (yes, I got them to send me a full set of schematics back then...). It uses a WD1797, which was a fairly common floppy disk controller. The drives are not specified, but they are Mitsubishi. I tried removing them but no luck. The bottom mounting screws are inaccessible without a significant disassembly of half of the unit. Perhaps a downside of having a pre-production unit ... sigh      I'm not up for doing that right now.

[RoGeorge]

Not sure why dismantling the 5.25 FDUs, do you plan to replace them with 3.5?

In my experience the 3.5 were less reliable, and the DD (720kB) 3.5'' were rather rare even back then, when compared to the 1.44MB ones.

The FDU pinout for 3, 5 or even the 8'' was the same IIRC, only the connectors were different.  The few signals needed, Step Dir and Side Select for heads, Read, Write, Idx, Motor on, etc, are well known and documented, there is no need to reverse engineer that or the pinout.

[precaud]

No, not "dismantling the drives"; dismantling the internals so the drives can be removed, to see the model number, to clean the heads, replace them, whatever.

[m k]

The interface is actually pretty simple and the drive is merely a spinner.

There are two possibilities, a track write or a sector write, read is trivial.
Today's MCUs have no problems timing those, no matter what.
Only possible problem is unknown sector interleaving but it can be analyzed when formatting happens.

Since a floppy is so small a thumb drive can hold a library of them.
Surely there is also an emulator with a display and some buttons.

[Deni]

In use, there is a lot of disk activity, swapping program modules in and out. Really slows things down. This thing would benefit hugely from an SSD.

These USB floppy emulators won't be any faster, since they emulate physical drive mechanics in order to fool floppy disk controller...

[precaud]

These USB floppy emulators won't be any faster, since they emulate physical drive mechanics in order to fool floppy disk controller...

Well if that's the case, I won't bother with them now. Thanks for the headsup.