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Thread: Quick and dirty floppy adapter for Tandy 1000s with power-over-cable wiring

  1. #1
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    Default Quick and dirty floppy adapter for Tandy 1000s with power-over-cable wiring

    One of my side projects lately has been coming up with ways to convert a bare Tandy 1000 HX motherboard into a working test mule for expansion boards and whatnot. It's reached the point that it was time to tackle assembling some kind of custom cable or adapter to connect a firmware-modded Gotek to use as a floppy drive. I was in the process of debating between a few different strategies when a light came on for a quick, easy, and reversible way to do it that just needs a 2x17 (or longer cut to length) long-tailed wirewrap or "stacking" 2.54 mm pitch female header and a piece of wire. (That part may be optional if your Tandy has standard power connectors available to tap or split.)

    Step 1:

    Pick an orientation for your header. Locate what pin will engage with pin 1 on either the motherboard or the floppy drive, and using a pair of needlenose pliers bend the first six pins (technically the first one is optional, it's NC) from pin 1 and the last three pins from pin 33 on the "odd" row down horizontal. Don't cut them off yet.

    Step 2:

    If you want to draw 5v for your floppy from the motherboard solder a wire to any of pins 3-11. Pins 29-33 will have 12v on them, tap that if you need it. (A Gotek doesn't need it, a real FD probably will.) The other pins on the odd side, 13-27, are grounds. I checked on the Gotek and the ground lines on the floppy power plug are common with the ground pins on the signal plug, so for that at least there's no need for a ground wire to go to the power connector.

    How long you make these wires depends on where you intend to put this header. If you're putting a Gotek on the same chain as an original Tandy 3.5" drive you can put the header directly on the drive's signal pins; then you'll only need an inch or two of wire to loop over to the 5v line on the power plug. If instead you'd rather convert all the cabling in the machine to be safe for normal drives then you might want to stick the header on the motherboard's connector; in that case you'll want power wires long enough to run to your drive bays.

    (I don't have a complete Tandy with this sort of wiring around to know if there's actually clearance to fit it in the motherboard plug. That's how I did it on my Frankenstein machine because I have no Tandy floppy drives; if I add a physical floppy to the internal chain along with the Gotek it'll be a standard one so I might as well keep the power off the signal cable in the first place.)

    After this you'll probably want to cut or tape off any power pins you're not using to avoid the risk of shorting them.

    Step 3:

    Solder a connector to your power wire that will engage with the power plug pins. Again, for the Gotek I only needed to populate a single wire so I just used one pin of the chunk of stacking connector I cut off when I trimmed a 2x20 down to 2x17, but if you have the correct locking plug lying around by all means use it.

    Step 4:

    Plug everything together, making *sure* you get the pin 1 orientation correct. Here's a few pictures:

    First smoke test of the idea:

    smoketest.jpg

    Close-up of the modded header in the motherboard connector. I'm drawing the power for the Gotek with that test clip:

    close-up.jpg

    The complete mess after I soldered in the power wire. Again, I'm using the "long wire" configuration because the header's going in the motherboard, not on the drive. (Also note I'm using this really long "universal" floppy cable here, and because of the orientation of things I decided to plug the "B-drive" connector into the motherboard and use the "motherboard" connector for the drive. It doesn't matter because the Tandy uses Shugart wiring/jumpering instead of using the twisted cable for A:

    complete-assembly.jpg

    Up and working. I went ahead and installed an OLED into the Gotek while I had the soldering iron out for the power cable.

    finished.jpg
    Last edited by Eudimorphodon; November 8th, 2019 at 05:43 PM.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  2. #2
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    I can recall a time, years ago, when my dad tried to replace one of the floppies on my HX (it was still his at the time), and he didn't know about the power over cable issue. Fortunately, all he did was smoke the drive.
    Well, by B: drive is having read issues now. I'm going to try cleaning the heads, but if it needs replacing, I was thinking of building a custom cable of my own and just sticking a normal 1.44MB floppy in it's place. I want to keep the original cable intact so I can restore it if I need be (I don't like destructive mods).
    Though I've been thinking of getting a Gotek and making a ribbon for that external floppy connector, that way I don't need to drag my floppy disks around when I go to retro-computer meetings.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  3. #3
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    Quote Originally Posted by blackepyon View Post
    Well, by B: drive is having read issues now. I'm going to try cleaning the heads, but if it needs replacing, I was thinking of building a custom cable of my own and just sticking a normal 1.44MB floppy in it's place. I want to keep the original cable intact so I can restore it if I need be (I don't like destructive mods).
    If there's enough space for it this stacking header idea should let you use the original cable. (I plugged it into the motherboard header on my frankenstein because I don't have any original drives, so there's no reason to let the power onto the cable, but it should work at the far end as well.) You'll just need to run both 5v and 12v to the power connector for a real floppy. (The Gotek only needs 5v.) Sticking the header on the drive's connector will make the cable sit about half an inch further back, I don't know if the space is tight enough in the HX's drive barn for that to be a problem.
    Last edited by Eudimorphodon; November 12th, 2019 at 10:01 AM.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  4. #4
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    Quote Originally Posted by Eudimorphodon View Post
    If there's enough space for it this stacking header idea should let you use the original cable. (I plugged it into the motherboard header on my frankenstein because I don't have any original drives, so there's no reason to let the power onto the cable, but it should work at the far end as well.) You'll just need to run both 5v and 12v to the power connector for a real floppy. (The Gotek only needs 5v.) Sticking the header on the drive's connector will make the cable sit about half an inch further back, I don't know if the space is tight enough in the HX's drive barn for that to be a problem.
    It's a bit tight at the back end, but there's enough room to squeeze something in. dJOS has a small PCB in his Tindle shop that does this https://www.tindie.com/products/cybe...gotek-adapter/ , but the power header might need to be adjusted depending on the floppy one wishes to connect.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

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