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Author Topic: Amiga 500 -1.3- external FDD (cable and boot) - almost a tutorial  (Read 1090 times)

Description: DIY, my way

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Offline giobbiTopic starter

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  • Join Date: May 2021
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hi friends,

maybe it was discussed many times, I'm not sure (and I'm new here - and someway new to the Amiga universe too, actually...) but I didn't find anything about that, and so I thought somebody could appreciate.

I was looking for an external floppy cable schematics, and (my fault, maybe) I didn't find anything like tutorial/instructions/DIY. After some research I've found a way to build a cable on my own and how to boot from an external drive. I want to share with you my experience, just in case anybody would need it.

Everything I'm explaining here was tested on my environment. You only need basic parts and some soldering skill.


If you fry your Amiga doing anything explained here, you're the culprit of the s**t you did, don't blame me LOL

This is the easiest part: you only need to use two sockets (the ones with round pins, possibly) in order to cross two CIA pins. The CIA you need to remove is the 8520 closest to the internal floppy cable connector.

Swapping the pins #13 and #14 will force the Amiga to boot from the external disk (note that probably the internal drive won't be accessible, because of its internal setting).

Solder two wires on the pins #13 and #14 on every socket. I suggest to clip the side of the lower socket a little bit and solder the wires laterally.
Then use a switch two ways, two positions, to swap the two signals. See the "example.jpg" picture attached for more info.

Now insert the two socket one into the another: be sure the pins #13 and #14 of the upper socket are not touching the same pins of the lower socket.
Put the CIA into the upper socket, and the whole "tower" in the Amiga socket.

You can make a simple cable (just the cable, no electronic components) to connect a Lotharek/Gotek/etc. floppy drive emulator, or a real 1.44 Mb floppy disk (use a stock, PC drive: it will not work with the Amiga drives).

Note: the DB23 connectors are quite rare and they cost a lot (I mean: too much). But you can make one: see the attached DB23M.jpg about how to make a DB23 male connector out of a common DB25 one (like the one used for the parallel PC printer).

This is the connection schematic:

Connect together the GND and use one more wire for the FDD power socket. Take the +5V from the pin #12 of the Amiga DB23 connector. Most real PC drives (at least the "modern" ones) don't use the 12v.

(Stock FDD 1.44 Mb drives usually already are; Lotharek, put switch #2 = ON, other = OFF, Gotek = should be the 2nd jumper,
I'm still waiting mine and can't say for sure).

 1   |  34
 2   |  30
 3   |  GND
 4   |  GND
 5    |  GND
 6   |  GND
 7   |  GND
 8   |  16       
 9   |  10       
10   |  n.c.
11   |  02
12   |  +5V.
13   |  32
14    |  28
15   |  26
16    |  24
17   |  22
18   |  20
19   |  18
21   |  12     
22   |  08

Hope this help!

EDIT -- Tested with the Gotek I just received from Aliexpress, works fine.

EDIT -- For some reason it stopped working with the phisical floppy disk 1.44 Mb. I don't know why. The disk appears on the Amiga screen as "DS1:BAD" and there's nothing I can do with it.   
I'm sure it worked and I tested it extensively (because I didn't expect it was so easy and I didn't believe the luck I had, perfectly working at first try).
I tried with many working floppies, three different FDD, same model, NOS. I've built another cable, just to be sure. Nothing.

BTW the 1.44 Mb FDD I used for test (the one that worked for a couple of days and then no more) now it's inside my Amiga 500. The original disk proved to be too picky and didn't work as espected, rejecting good floppies, etc. 
I connected the replacement unit (PC drive, 1.44 Mb) using the toms01 board (https://gitlab.com/toms01/1581-pc-drive-adapter). That board was made for C= 1581 drives (and 1581 replica), but proved to work fine for Amiga FDD replacement too. You just need to close the right window on the floppy with some tape to force it to detect the floppy as 720 Kb (or use a 720 Kb floppy, but nowadays they are quite hard to find).
« Last Edit: June 30, 2023, 02:16:49 AM by giobbi »