Connecting a 3.5" floppy drive to an Amstrad 464 without modifying the drive or DDI-1

Created on: 16-12-2020  By Gee
Quite some time ago I bought a DDI-1 interface to use with my amstrad 464's. Just the interface with the ribbon cable, no FD-1 floppy drive. Why did I buy that by itself? well I wanted to clone it and/or make it work with a regular 3.5" PC floppy drive. So far, I have it partially working! But it took until I eventually bought an FD-1 to make sure the DDI-1 interface was in fact working.

The birds nest of wires

So you should be able to see from the pictures above that this device has been made entirely on a prototype board. The wires look like they're going everywhere and connected to everything. Hopefully they aren't!
I started making this board by noting down the pinout on the regular PC floppy drive and then the pinout on the FD-1 drive. Most of the connections are the same, but the cable is flipped upside down. However, there are some 5v lines going down the ribbon to the DDI-1 interface to power it.
I read somewhere that both of these conditions were created by Amstrad to try stop people from being able to just plug and play with a PC drive as I am attempting to. Wither this is true or not, I don't know.
I set about making my prototype board using what I had written down. Put it all together and... nothing. in fact, one of my power lines was loose and then short circuited causing some smoke. I thought I had destroyed my DDI-1 or worse, the Amstrad. I made sure the ribbon cable was on correctly and eventually I got some drive spin. It didn't sound like it was seeking at all, but the drive was spinning. no lights. no reading.

Help Required, not much given

I had no idea what was going on with this device and then asked on the forums.
I got two people answering, one person was trying to sell me a board they had already made to do the same job (and more), not offering any insight as to what the problem might have been, And Bryce the ever knowledgeable character who I think didn't understand my schematics (I'm not a pro! what can I say).
I gave up with the project for quite a while until I noticed an FD-1 drive come onto ebay cheap. It was in fact just the shell without a drive. Just what I needed. After winning that and having it arrive in my house, I set up putting a gotek drive in it to make sure my DDI-1 was working and it was! I got to load some disk images on my 464 for the first time. Sadly it was with using a gotek drive, which never appeals to me. Whilst I was using said gotek, I remembered that I had taken a drive out of my 8256 previously to replace that with a gotek too. So in went a 3" drive into it's enclosure. I now own a complete DDI-1 and FD-1 interface and drive, minus some case screws sadly.

light at the end of the tunnel

Now came the brain fart. If this drive was working fine, and I can trace where all the lines are going from the interface to the inside of the FD-1 case, surely that should help me work out where i am going wrong?
I went over each line and noticed something odd. Two of the lines were connected that I wasn't expecting to be. One line (pin 8 I think) wasn't connected to anything from what I could see. The line that I had going to pin 8 was in fact going to pin 10, which already had a line going to it. A little de-soldering, and soldering back on later. I powered up my drive and hey presto! I can now read a 3.5" floppy on my Amstrad 464 without modifying either the drive or the DDI-1 interface.

The tunnel got a bit longer

The success wasn't to last long, as when I was playing SimCity and I went to save, the computer froze and the disk drive cranked away. Never ceasing to flash the read/write light. So all is still not well with this board. I will do some more tracing of circuit boards to figure out what is going on with all the lines to see if I require some more circuitry, which I expect I do. Why else wouldn't it work?

More help still required!

If you have worked on a similar project and have an idea as to why this isn't working. Please use the Contact page to drop me an email and let me know where I'm going wrong.