My OSI 610 build - Expansion for the OSI 600

[HigashiJun]

I guess it's the ELK...

[rubber_jonnie]

I guess it's the ELK...

Elf

Cosmac ELF II replica

[stephen_usher]

Would you believe that I already have one lined up...

Surely not! Hehehe!

[PhilC]

Would you believe that I already have one lined up...

Surely not! Hehehe!

I'd be surprised if he only had one lined up

[rubber_jonnie]

Surely not! Hehehe!

I'd be surprised if he only had one lined up

It's true, I do have more than one lined up, and may add an Atom replica to the mix, which is your fault @PhilC

I am also looking to build a ZX80 replica too.

[HigashiJun]

Elf

Cosmac ELF II replica

Oops, my bad...

From:

ELK.jpg (69.15 KiB) Viewed 800 times

To:

ELF.jpg (316.32 KiB) Viewed 800 times

[rubber_jonnie]

Elf

Cosmac ELF II replica

Oops, my bad...

From:

ELK.jpg


To:

ELF.jpg

[rubber_jonnie]

Not content with getting it all working, I'm modding it to support double sided drives, meaning each FDD treats a side as a disk. Should be interesting, and apparently it also supports 2 drives, so ultimately drives A to D.

More later.

[rubber_jonnie]

OK, so the double sided mod is done

The mod is done in this corner of the 610 board indicated by the red square:

Screenshot 2025-06-22 at 10.44.14.png (2.11 MiB) Viewed 769 times

You can see a number of square jumper pads. The links and cuts (X) on top are shown here in green:

Topside_2.jpg (226.41 KiB) Viewed 769 times

It's necessary to add a 1K resistor at R7. The underside cuts are shown here in red with the topside cuts (X) and links in green:

Screenshot 2025-06-22 at 11.02.05.png (2.14 MiB) Viewed 769 times

The main difference once this is done is the need to use a floppy cable with a twist rather than a straight through one.

I need to download some double sided disk images to test, but basically it means that my Gotek (or any other double sided drive) will work as 2 drives, so A: & B: with each head being a 'drive'. If I add a 2nd drive it will work as C: & D: in the same manner.

It's a bit like double sided drives for the BBC B.

More testing to be done but it is happily booting from the Gotek as before with the new cable, so I haven't broken anything

[rubber_jonnie]

OK, so I have been able to finish off assembly of the 600&610 with the arrival of some rubber feet today:

IMG20250701113257.jpg (380.73 KiB) Viewed 743 times

IMG20250701115542.jpg (403.63 KiB) Viewed 743 times

It's all buttoned up in an OSI sandwich

And I have a pair of Goteks working double sided:

IMG20250701133759.jpg (203.58 KiB) Viewed 743 times

IMG20250701133804.jpg (369.72 KiB) Viewed 743 times

It is also sort of working with a 5.25" floppy drive, but it's not 100% so more work to do on that.