ITXPlus: A ITX Sized Macintosh Plus Logicboard Reproduction

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May 22, 2025 - 01:15

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max1zzz

Well-known member

I haven't done project thread in a while as writing is not my favourite past time but people seem to enjoy them so here it goes

ITXPlus is a Mini-ITX sized Macintosh Plus logicboard clone that can be be assembled to a working state with no original parts and is intended for new build systems in modern cases

ITXPlus features a onboard VGA output using GuruThree's Pico based video converter, power from standard 24pin ATX power supply, a onboard 50pin internal scsi header and 4MB of solderd RAM

ITXPlus also makes used of DosFox's discreet replacement for the Sony Sound IC and my implementation of his SCHWIM IWM bypass in a PLD as well as pgreenland / quortan's ATTiny based RTC replacement and Porchy / Hkz / Bolle's reverse engineerings of the Macintosh Plus PAL's

(I hope I haven't forgotten to mention anyone's elses work I have used....)

As it is designed to use a SCHWIM based IWM bypass it will not support floppy drives out of the box however a expansion heder is provided with all the signals required to connect a real IWM should you want to do this

With execption of the 68000, connectors and a few other little bits the board is fully surface mount, I almost went with a surface mount 68000 too but was convinced otherwise as it means the nice gold capped ceramic 68000's can be used Smile :)

The board will look something roughly like this:

Though as you can see there is still most of the routeing work to do so things may get moved around a little

Finally to answer the inevitible question: Why base it on the Plus? why not the IIci? or the SE/30? I chose to base it on the plus simply because it can be built with no original parts, this is intended to be a project build not the fastest possible mac out there.

When finished the design will be fully open source and posted to my GitHub Smile :)

cheesestraws

Well-known member

I've been really looking forward to the first 'no original parts' board build. This is a milestone and a half. Well done.

luRaichu

Well-known member

Next: A Macintosh Plus built without original parts. I'm sure they're still making b/w CRTs somewhere in China

max1zzz

Well-known member

cheesestraws said:
I've been really looking forward to the first 'no original parts' board build. This is a milestone and a half. Well done.
Click to expand...

Thanks

Though strictly speaking I think DosFox is the first one to do a "no original parts" build - he built a clone board based using my original Plus Reloaded board and most of the other bits mentioned above

cheesestraws

Well-known member

Sorry, I meant 'design', as in actually a new board with new bits on.

Gothikon

Active member

Fantastic!

max1zzz

Well-known member

Getting there! Still quite a bit to do but it's finally at the point there are more red and green lines than white lines Smile :)

mattsoft

Well-known member

cool idea and cool project!

max1zzz

Well-known member

MLB is done! Just need to draw up the riser with the keyboard / mouse / serial ports on it

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joshc

Well-known member

This is cool. I don’t need it but I want to build one… this seems like a great way to get a Plus without having another compact to find space for. A slim ITX case could be used.

Although surface mount isn’t my favourite kind of soldering but I can understand why it was based on SMT.

This would lend itself well to a kit where all the parts needed are supplied… Thinking face :thinking:

max1zzz

Well-known member

It may actually be possible to build one of these with more TH parts, Probably not fully TH but there might just be enough space to squeeze in DIP parts for all the logic and PAL's and maybe the SCSI controller, ROM / VIA / SCC would have to stay as SMT parts though as there just isn't the space for the DIP packages (Though maybe TH PLCC sockets could be used.......) It's something I might look to do in the future as I was quite surprised a how much free space there actually is

max1zzz

Well-known member

Boards have been sent off to JLC, hopefully I should have them in hand by the end of next week Smile :)

adespoton

Well-known member

max1zzz said:
Boards have been sent off to JLC, hopefully I should have them in hand by the end of next week
Click to expand...

How large a run are you doing?

max1zzz

Well-known member

At the moment just 5 to see if they work, I may do a larger run later though (It will also be open source so you will be able to make your own too Smile :)

)

max1zzz

Well-known member

PCB's are here!

Big Ben

Well-known member

This is the call for testing and glory!

*ahem*

Looks great! Can’t wait to see it in action, nice work!

max1zzz

Well-known member

Big Ben said:
This is the call for testing and glory!

*ahem*
Click to expand...

That'll be tomorrows job Smile :)

All the non programmables (and the ROM) are soldered down, will get all the PAL's programmed and installed tomorrow. Also still waiting for a pico to arrive as my spare one is AWOL

max1zzz

Well-known member

It's late and I'm not doing a full write-up tonight, but I'll just leave these here (excuse the potato video, it's that or a massive file and I cba with trying to compress it right now)