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DIY Model III/4 daisy chain expansion port cable

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Maybe someone at sometime will find this info useful.


The Model III and 4 has a single 50 position I/O bus port for expansion.  A company called Alpha Products used to sell a cable that allowed you to daisy chain multiple peripherals on that port.  Unfortunately those haven't been available since the mid 80s.


The port is a 50 position card edge.  50 position ribbon cable and female connectors are easily sourced.  Amazon has the best price on the female connectors; less than $20 for 5.  Anything with a 50 position card edge is next to impossible to find these days.  Also each "finger" on the board needs to connect from top on one side to bottom on the other.  The Radio Shack Hi-Res board came with one as a pass through.


I recently found a source for dirt cheap prototype trans boards that can be modified in about 1 minute.


Syntax PC-622.  These are 62 position and already have the reverse side connected.  A cutting wheel on a Dremel will easily make it into a 50 position.  You'll also want to bevel the edge a bit with a flat file.


My port currently has the Hi-Res board (looped from inside like factory), FreHD (hard drive) and an Orchestra 90 all getting along together.  I also have a mouse interface for CAD which I'll try as soon as I get a RS mouse.







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Hello Turbo-Torch,


1. Vintage Tandy 5.25" 360K External Floppy Disk Drive for Model 1000 PC, 25-1060

2. Radio Shack 5Mb Master hard disk

3. Model II Disk System. (8 inches drive)


I have all of them (Yes , 3 of them). The only missing is key for Radio Shack 5 Mb Master Hard Disk. Missing 3 fuses on the back of Model II Disk System.

I want to know if any those 1 of 3 or all of them has matching ribbon cable like you has in those photo above ?


Thank you for reading my message above.

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I had the 25-1060 back in the 80s (and the 3.5" 25-1061).  Those drives are only for the Tandy 1000 EX and HX.  They used a special cable that also carried power to the drives.  IIRC, the drives were normal but used an adapter board inside the housing.  I also remember the cable wasn't a ribbon, it was black and round.


The hard disk attaches to the 50 position I/O port of the Model III.  The cable pictured above would just need a different connector on one end to attach to the hard disk's pin connector.


I'm not familiar with the Model II 8" drives or the cable required.  I do have some bare 8" drives that I intend to make work with my Model III one day...that will require a 50 to 34 pin converter board, special power supply and custom cables.

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25-1060.  I can paste photo at the back of this drive. That I do NOT have that specific ribbon cable that hooked to an VERY SPECIFIC shape port ! Do you know where to find a key and 3 fuses ? Any idea where ?


Edited by Caterpiggle

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Your picture didn't show up.  IIRC, the 20-1060 cable used female card edge connectors on each side...might have been a standard 34 position?  You would need a wiring diagram to see if it follows a standard drive cable layout.  Also, I don't know if a regular ribbon cable can handle the current to power the drive.  And like I said, that drive only works on the EX and HX computers.  I think you can take the drive out of the housing, unplug the adapter board and then use it as a normal internal disk drive in other computers.


I doubt you'll find a key for the hard disk.  Easier to replace the key switch with a new one or install a regular on/off switch in its place like the later versions.

I don't know the fuse size or ratings.  If you Google search for info on the drive, there are scanned service manuals online.


vcfed.org has a Tandy forum that is very active.  You may be able to get the parts and info you need there.  Unfortunately the forum software is not friendly to new users.  Each time you make a post, it takes a day or two for it to show up because a moderator has to approve it, so you'll need to be patient.  After you make several legitimate posts, they give you normal access.

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