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Thread: Tandy Model III - Identifying 5 1/4 Drives

  1. #1
    Join Date
    Apr 2019
    St. Louis

    Question Tandy Model III - Identifying 5 1/4 Drives

    I recently acquired a Tandy Model III that I have been working on. So far everything is in great shape inside. This one was upgraded at some point with 48K, two disk drives, and a Omikron Systems board for CP/M capability. The only real issue is the floppy drives are having issues reading disks.

    I can get NewDos/80, TRS-DOS, etc. to boot to the main splash screen, but after entering the date and time the drive will error out the disk. I have tried flipping drive 0 and 1 with the same results. Both drives have the same issue reading disks around the same spot. I'm thinking that the drives both need to be re-aligned, but that's my best guess at this point since I'm unfamiliar with the model of the drives. I find it odd that they both error at the same spot, but I'm guessing they both drifted out of alignment around the same time. Not sure if that is normal or not. I'm not sure if they are double sided or not as I have not been able to test them. They could be 80 track drives, but I'm not sure. I did clean the heads and drive rails. I also lubed the rails up with dry slide. I can see and hear the drive moving so I don't think it's the rails sticking. They also have the switches on the front of the drive that locks the drive from being opened. If it does anything else I haven't noticed. Just an odd piece that sticks out to me.

    Next I was going to try replacing the flex cable for the floppy controller board since this is a common failure point, but the controller board has a flex cable directly soldered to it and the end plugging into the motherboard has pointy teeth rather than it being flat. For now I'm skipping that since it actually looks fairly decent and it would need to be de-soldered to replace it anyways. It looks a lot better than the non-working ones I have seen in the past.

    I'm also trying to identify the floppy controller board since it is a little unusual. I don't have a picture of it, but when I was in there I think it had the name Displayed (c) 1982. It's entirely silver in color. I can get a picture of it if needed. Should have snapped one when I was in there...

    I will attach a few images I took as well.

    My questions summed up are:
    1. Any ideas what model of drives this system is using?
    2. Any ideas what floppy controller card is in this system?
    3. Any ideas on what the issue with the floppy drives are?

    Any input is appreciated thanks!


    Top of Drive.jpg

  2. #2


    The floppy drives look like Nascom 1 computer Floppy Drives sold on OEM by TEAC to NASCOM/LUCAS systems then later called System 80 computers.

    The problem if they are (you need to pull one and look for markings to confirm) is that teh Nascom Drive is
    Single Sided Quad Density 80 Tracks drive so 720K and likely not compatible with a more standard size like SSDD floppy your likely to be using right now.

    from what I know and found it was a floppy used on the Nascom 3 model computer as seen in this image

    So nothing wrong with hardware or software , just not the rights ones to use with each other.
    do you have the original floppies that came with the computer from previous owner?

    Also looking forward to identifying your floppy disk controller.

    Last edited by Patrick Bureau; March 21st, 2020 at 06:03 PM. Reason: forgot my references
    Gaming: i7-8700K, 16GB, 1TB SSD, RTX 2060, Dual 27" LG IPS Monitors.
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  3. #3
    Join Date
    Mar 2012
    Augusta, Georgia, USA


    I ran into the same thing and it confused me for a while also - someone gave me a Model 4 with two TM100-4's (80 track double sided). If if's dual sided, there will be two sets of wires to the heads, stacked on each other (your picture is top down so I can't tell).

    I had to make special versions of the boot disks that are 80 track using the TRS80 emulator on a PC to boot up and use it. If it's your only TRS80, it's not that bad, but if you are trying to interchange disks with other machines, it's a pain since it won't boot normal disks. I ended up putting regular 40 track drives as the boot drive and the 80 track drives as the second drives in mine...

    However, it's nice that the disks will hold 2x (or 4x if double sided) the amount of data. LDOS and NewDos/80 2.5 can handle this.

  4. #4
    Join Date
    Apr 2019
    St. Louis


    Wow! What a find! I'm glad to find that the issue was easier than I thought!

    Background wise I have almost no info about the system. Bought off of Face Book market place. Far as I could tell it was the grand daughter selling the device while cleaning out the grand parents house. She didn't know anything about it and I think the grand farther was too ill to remember anything about it. It must have cost a fortune at the time considering all the upgrades! Given that info I have none of the original software for it at all and the boot disks I'm using are defiantly made for 40 track single sided drives.

    I do have a few options for making new 80 track disks. I have a dos computer with a 1.2MB High Density Drive. I believe I can set this to write in 720KB mode to write a boot disk from an emulator. If I remember correctly that can cause issues since the magnetic heads are stronger and narrower in a High Density drive. Kinda a write the disk once situation. Since I would just need a boot disk, I think it would be fine as long as I didn't need to write to it.

    Next option. I do have a GoTek drive flashed with flashfloppy and an apter to card edge. I could use that as drive 0 and make a new working boot disk in 1. I believe that would be easiest and have less issues than option 1.

    Should mention that I do have some Tandon 40 track drives from a Model III that doesn't work. I'm fine with using just the 80 track drives in just the one. No need to move software around between the 1 in my case. I'm guessing the floppy controller board would support Tandon 40 track drives as well? I was planning to use the GoTek to load games and the like as drive 2. Do you think pin one on the bottom edge connector is closest to the outside edge of the case? It's not labeled on board.

    I got some images of the Floppy Controller Board. It's listed as "(cr) 1982 Displyed Video". I also took some of the inside of floppy drive, figured out it is double sided. There is two heads in there, Snapped the Serial board that I put in, snapped the mother board, and took a snap of the Omikron Mapper since it's in upside down compared to the mother board. I will attach them all below as well.

    Floppy drives did have a sticker with the model number on the back! It's a Teac FD-50F-71. I can find almost nothing online, but I did find a maintenance manual listed the drive model as 80 tracks double sided. Seems that the Teac FD-55 series was much more popular being used by IBM and all that.

    New questions for this time:

    1. Best method for making 80 track boot disks? (Doesn't have to be what I suggested.)
    2. Any info on the Floppy Controller Board?
    3. Is Pin 1 on Floppy Controller Board the pin closest to the outside edge? (That would match the orientation at the top.)
    4. Does the Floppy Controller Board support 40 track drives as well as 80 track?

    Again any info is appreciated!

    Mother Board:
    mother board.jpg

    Omikron Mapper:
    Omikron Mapper.jpg

    Floppy Controller Board:
    Displayed Video FCB and Serial Board.jpg

    Floppy Drive Insides:

    Floppy Bottom.jpg

    Top (under board):
    Floppy Inside Top View.jpg


    Back of Drive:
    Model Number.jpg

    Source for model info:

  5. #5
    Join Date
    Feb 2015
    Cleveland, OH, USA


    Quote Originally Posted by psg4 View Post

    New questions for this time:

    1. Best method for making 80 track boot disks? (Doesn't have to be what I suggested.)
    2. Any info on the Floppy Controller Board?
    3. Is Pin 1 on Floppy Controller Board the pin closest to the outside edge? (That would match the orientation at the top.)
    4. Does the Floppy Controller Board support 40 track drives as well as 80 track?
    You can use the RS floppy controller to control SSDD or DSDD (160K or 320K, nominally) drives, such as the Tandon 100-2 or -4. Higher densities are not supported. Info on the controller board is contained in the RS technical manuals. PM me if you can't find a copy.

    If you want to use a 1.2 Mb drive to format and write one of the lower densities accept the fact that it may not be successful, not only due to the difference in size of the track but due to the difference in media itself on a lower-density disk. Try to find a SSDD or DSDD (not HD) 5.25 disk to write to, and before you put it in the drive make sure to do two things: Use a cleaning disk and some isopropyl alcohol to clean the disk heads, and using a large and strong permanent magnet wipe both sides of the floppy to erase all prior markings.

    I'm not sure what your FC looks like but if the connector is a card-edge connector there will be a split or a keyway toward one end; that end is pin 1. Again, refer to the technical manuals.


  6. #6
    Join Date
    Sep 2011
    Melbourne, Australia


    Those Teac FD-50 drives are very old and were originally used by Radio Shack in export Model I 26-1160 and 26-1161 240V drive units.

    They are not a good choice for the Model III because they only step at 30ms, and the operating systems for the Model III are set up to step at 6ms. The upshot of this is that the boot track will read, show the sign on and then not proceed. Displayed Video, who would have supplied this upgrade back in the day would have supplied special patched versions of TRSDOS or Newdos to step at 30ms. If you've lost those original disks then copies of normal Model III operating systems won't work properly.

    Chances are both your Teac drives are OK they just don't step fast enough.

    They may be double-sided and 80 track Teacs, but all use the same stepping mech which is not designed for stepping faster than 30ms.

    Hope this helps,

    *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

  7. #7
    Join Date
    Mar 2013
    Chaffee, MO


    An easy test to see if your Model 3 will boot into Radio Shack ROM Basic is to hold the
    BREAK KEY depressed, and power up with NO floppy's in your drives. If you see the
    CASS?? message displayed, release the Break Key, and depress the ENTER Key 3 times.

    If that works you should be able to patch the OS of choice for the stepping Rate of 30ms.


  8. #8
    Join Date
    Mar 2012
    Augusta, Georgia, USA


    I was able to make disks in my DOS PC with a regular PC HD 5.25 drive (it's one of those Teac combo 3.5/5.25 drives).

    Using TRS80.EXE emulator (in DOS) I use the FDDx_720.DSK (x is 0 or 1 depending on the drive being A or B) to make 80-track disks. To make 40 track disks, use FDDx_360.DSK which will double step the heads. You'll want to use F6 to speed up the emulator to "unlimited" or this takes forever.

    I have the advantage of being able to easily erase disks with my ZoomFloppy/Nibtools setup (nibwrite -u to unformat). I don't think a magnet really erases a disk effectively.

    However, for the 80 track drive, you shouldn't have to worry about the erase. That will only come into play making a disk for a 40-track drive using the PC 5.25 drive and double-stepping on reused disks.

    I never had to mess with the step rate OS patches, but it sounds like your drive may need that... I use NewDOS/80 2.5 on my MIII and that is probably an option if you need it. You'll need to get very familiar with the PDRIVE command.
    Last edited by rittwage; March 22nd, 2020 at 07:57 AM.

  9. #9
    Join Date
    Mar 2013
    Chaffee, MO


    There are Several good Emulators you might want to play with. These can create Disk Images
    for your system. (Emulators in no particular order.....)

    1. XTRS by Tim Mann
    2. TRS80GP by George Phillips
    3. TRS80 by David Keil
    4. SDLTRS (2019) by Jens Guenther
    5. TRS32 by Matthew Reed

    The Stepping rates can be set inside most Emulators to 6ms, 12ms, 20ms, or 30ms. You also can attach
    Virtual or real Floppy drives to the Emulators.

    The Omikron Mapper has three version from the information I found:
    Omikron Mapper I Model 1 & 3 (40T, SS, SD, 83K)
    Omikron Mapper II (40T, SS, DD, 134K)
    Omikron Mapper III )40T, SS, DD, 190K)

    And I only have one definition for the CP/M Floppy's. But, others can be generated if you
    can get some .TD0 or .IMD files of your floppy's.

    BEGIN TRS1 TRS-80 Model 1, Omikron CP/M - SSSD 48 tpi 5.25" - 128 x 18
    SIDE1 0 1,5,9,13,17,3,7,11,15,2,6,10,14,18,4,8,12,16
    BSH 3 BLM 7 EXM 0 DSM 71 DRM 63 AL0 0C0H AL1 0 OFS 3

    # TRS1 TRS-80 Model 1, Omikron CP/M - SSSD 48 tpi 5.25" - 128 x 18
    diskdef trs1
    seclen 128
    tracks 35
    sectrk 18
    blocksize 1024
    maxdir 64
    skew 4
    boottrk 3
    os 2.2

    # libdsk
    description = TRS1 TRS-80 Model 1, Omikron CP/M - SSSD 48 tpi 5.25" - 128 x 18
    cylinders = 35
    heads = 1
    secsize = 128
    sectors = 18
    secbase = 1
    datarate = SD

    cyls = 35
    heads = 1
    secs = 18
    interleave = 4
    bps = 128
    id = 1
    #rpm = 360
    rpm = 300
    rate = 125
    mode = fm
    iam = no

    In my TRS-80 stash, I have the following:

    │ │ ├── Omikron Mapper (1980)(Omikron).pdf.7z

    │ │ ├── Omikron 8 Inch Disk Driver (19xx)(Author Unknown)[CMD].zip

    │ │ ├── Omikron 8 Disk Driver for LDOS (19xx)(Author Unknown)[MAC].zip

    I have no clue if they would be of help.

    Last edited by ldkraemer; March 22nd, 2020 at 08:56 AM.

  10. #10
    Join Date
    Jan 2007
    Pacific Northwest, USA
    Blog Entries


    Unless you're interested in "keeping the looks", get rid of the FD-50 drives. They were an early attempt by Teac to produce a cost-reduced 5.25" drive compatible with the Shugart SA-400 series. Electronics weren't all that good and a plastic body (when everyone else was using metal). I'm a little surprised that yours may still be working.

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