Early Macintosh home brew 4MB memory upgrade board development
- Thread starter Golden Potato
- Start date
Finally, I can share the fabrication files for my RAM expansion board.
You can now build your own 4MB RAM upgrade and breathe new life into your Early Mac!.
Check out the full guide and download the files here
I made my best effort to assure it will work on a Macintosh 128K with all LB revisions, but it has not been tested yet.
Also, should work with the MacSnap SCSI board installed togheter, but testing is pending.
Arm yourself with a ton of patience and good luck with the assembly. Let me know how it goes
Enjoy!
You can now build your own 4MB RAM upgrade and breathe new life into your Early Mac!.
Check out the full guide and download the files here
I made my best effort to assure it will work on a Macintosh 128K with all LB revisions, but it has not been tested yet.
Also, should work with the MacSnap SCSI board installed togheter, but testing is pending.
Arm yourself with a ton of patience and good luck with the assembly. Let me know how it goes
Enjoy!
Golden Potato
Well-known member
YES!!!!! I’m so glad you were able to get the full 4MB working!
Thanks for humoring me by testing with the Mac Plus style refresh since we spent so much time trying to figure that out. I’m also glad you were able to simplify by using the system’s stock refresh. I would still really appreciate some guru explaining to me exactly how this refresh mode works for this DRAM.
Golden Potato
Well-known member
Looking forward to building one of these up, installing it, tossing my defective prototype in a box, finally buttoning up my Mac, and having some workbench space back 
Great work, Builder68!!
Great work, Builder68!!
Don't toss it yet! The RAM refresh configurator board I published is able to generate 1,024 refresh cycles according to the encoding you produce. I think we should test the 1024 refresh mode with a PCB prototype for the 2 MB RAM ICs we both have.Looking forward to building one of these up, installing it, tossing my defective prototype in a box, finally buttoning up my Mac, and having some workbench space back
Great work, Builder68!!
Haha, I hear you on the 'Mac Plus mode' satisfaction. It's like those old-school RPGs where you grind for hours to learn a super-powerful spell, even though a basic attack works just fine. I guess there's just something about the challenge and the sense of accomplishment, right? Glad we were able to figure it out, even if it took a bit of tinkering!
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Golden Potato
Well-known member
Oh that’s true! It’s been so long since I’ve looked into this, I’d forgotten that we still haven’t tested the 1024 refresh mod for RAM ICs which require it!
You’re referring to the aux board? If so, I can try to get one made up and tie it into my prototype board.
For some reason, I haven’t been getting email notifications for posts to this thread since early October. Otherwise I would have been more active! I’ll check my settings…
It's not your settings, that forum feature is broken for everyone at the moment.
Golden Potato
Well-known member
Ah, thanks for the heads up. Guess I’ll just have to log on daily
Today, a new free and open-source PCB build based on just two 2Mb x 16-bit RAM ICs with a 1024 refresh cycle has been uploaded to my GitHub page.
This is now a single detachable 4 MB RAM board that, like other RAM cards for these Mac models, taps several signals via bodge wires with JST connectors and either piggyback sockets or pin headers soldered to components on the LB.
The expansion RAM can be disabled, and onboard RAM restored, via DIP switches on the card, so there's no need to detach everything if you want to run an app that requires the original RAM size.
The PCB shape and size have been designed with concurrent installation in mind alongside Demik's MacSnap SCSI replica board and potentially an accelerator board currently under development based on Bolle's Micromac Performer SE-Cl-PL board clone.
This design was the result of teamwork with Golden Potato, who places a special focus on making available to the retro community a free and open source RAM expansion board for early Macs using the fewest possible RAM ICs, reducing power consumption and increasing reliability compared to other RAM cards that use as many as 48 RAM x 1 address bit ICs to reach just 2 MB of RAM.
By the way, like the previous design release, this has been tested only on the 512Ke. Although I haven't found anything that would impede it from working on the 128K/512K models (64KB ROMs haven't been tested yet), there is no guarantee, and it may need Plus ROMs and some tweaking to the current PCB build to work correctly.
As I mentioned before, and just for fun and the joy it brings me to attempt totally unnecessary upgrades to my lovely 512Ke, I'm working on a reshaped PCB build of Bolle's Micromac Performer Replica that could be installed altogether with this RAM board and Demik's SCSI board.
The stock ROM (128KB) on my machine, with this RAM expansion and the SCSI board installed, is recognized as a Mac Plus. So, unless something else is escaping my understanding, the Performer board should work, right?
If it works, then a single PCB build could be made integrating everything, even the ROM-INATOR. A one-time, single, multi-purpose upgrade PCB for the Mac 512Ke!
This is now a single detachable 4 MB RAM board that, like other RAM cards for these Mac models, taps several signals via bodge wires with JST connectors and either piggyback sockets or pin headers soldered to components on the LB.
The expansion RAM can be disabled, and onboard RAM restored, via DIP switches on the card, so there's no need to detach everything if you want to run an app that requires the original RAM size.
The PCB shape and size have been designed with concurrent installation in mind alongside Demik's MacSnap SCSI replica board and potentially an accelerator board currently under development based on Bolle's Micromac Performer SE-Cl-PL board clone.
This design was the result of teamwork with Golden Potato, who places a special focus on making available to the retro community a free and open source RAM expansion board for early Macs using the fewest possible RAM ICs, reducing power consumption and increasing reliability compared to other RAM cards that use as many as 48 RAM x 1 address bit ICs to reach just 2 MB of RAM.
By the way, like the previous design release, this has been tested only on the 512Ke. Although I haven't found anything that would impede it from working on the 128K/512K models (64KB ROMs haven't been tested yet), there is no guarantee, and it may need Plus ROMs and some tweaking to the current PCB build to work correctly.
As I mentioned before, and just for fun and the joy it brings me to attempt totally unnecessary upgrades to my lovely 512Ke, I'm working on a reshaped PCB build of Bolle's Micromac Performer Replica that could be installed altogether with this RAM board and Demik's SCSI board.
The stock ROM (128KB) on my machine, with this RAM expansion and the SCSI board installed, is recognized as a Mac Plus. So, unless something else is escaping my understanding, the Performer board should work, right?
If it works, then a single PCB build could be made integrating everything, even the ROM-INATOR. A one-time, single, multi-purpose upgrade PCB for the Mac 512Ke!
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Joopmac
Well-known member
Awesome!!!
I made a Mouser cart for all the parts except the DRAMs (unverified, haven't received the order yet of course)
One question: Can this slide in/out without bending the frame aside? "low profile" enough?
Or a Performer Pro =)
Edit: Or a Gemini Ultra (II?)
I made a Mouser cart for all the parts except the DRAMs (unverified, haven't received the order yet of course)
One question: Can this slide in/out without bending the frame aside? "low profile" enough?
OMG this! Would be so awesome
Or a Performer Pro =)
Edit: Or a Gemini Ultra (II?)
Golden Potato
Well-known member
Thank you Builder68! This project has been a blast, and I’m happy to have cracked this with you.
I’m excited to see how far you can take these early Macs in terms of performance and upgrades!
nottomhanks
Well-known member
WONDERFUL WORK GENTLEMEN. This is crazy cool.
Joopmac
Well-known member
Builder, are you sure it's 2Mx16 RAM IC's? The AS4C1M16E5 i found are 1Mx16 = 2MB i guess?
EDIT: yes i misread, you indeed say 2MB =)
Ordered all the parts, this is going to be fun=)
The mouser cart is for 5x PCB, btw=)
Yes, you can use AS4C1M16E5 or AS4C1M16F5. Both should work. My chips are 60 ns (-60JC).
Yes, each one provide 2MBytes of RAM (16Mbits x 16 address bits)
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A Performer Pro would certainly be an extreme upgrade! But so far I believe no one has published a reverse-engineered accelerator board for the Plus with RAM cache, so for now the Performer-PL board reverse-engineered by Bolle seems to be the only option at this time.Awesome!!!
I made a Mouser cart for all the parts except the DRAMs (unverified, haven't received the order yet of course)
One question: Can this slide in/out without bending the frame aside? "low profile" enough?
OMG this! Would be so awesome
Or a Performer Pro =)
Edit: Or a Gemini Ultra (II?)
The RAM expansion board is indeed "Low Profile" enough to avoid bending the frame. But certainly, adding an accelerator board would forcibly imply bending it.
Are there any photos of version 3 completed? I am looking to compare parts. The Github page has a dead link for photos.
I ordered from the Mouser cart (thank you Joopmac) except that J11 and J12 headers are backordered and not in stock. I am guessing this header may work found on Amazon...
The PCB's I ordered were completed and shipped.
I ordered from the Mouser cart (thank you Joopmac) except that J11 and J12 headers are backordered and not in stock. I am guessing this header may work found on Amazon...
The PCB's I ordered were completed and shipped.
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