128K/512K Rechambered

[Trash80toG4]

Less sane fork of:

https://tinkerdifferent.com/threads/how-much-of-the-128k-512k-hardware-has-been-reverse-engineered.1630/

Mac Plus is the perfect platform for this insanity, who hasn't got one to spare? If you have two, but no spare, put 'em in a dark closet for a couple of months.

How many of a Plus donor board's components would be drop-ins for this 128K/512K Rechambered notion?
- Metal bar for chassis interface
- CPU
- ROMs - maybe, we've an 800k FDD in situ after all?
- A/B I/O connector
- KBD connector
- Mouse Connector
- External FDD Connector
- Sound jack
- DIN connectors
- Crystal
- reset switches
- RTC?
- Coil doohickies?
- Proprietary Silicon?

SIMM sockets? Underutilized, dirt cheap 256k keychain SIMMs should work well, no? Downside there would be interference with form factor of original upgrade boards? If that's the case, a low profile DIP RAM adapter board soldered onto headers in the SIMM socket thruholes may be low enough? But who's got that kind of upgrade handy?

Might a 16bit, high capacity ROM upgrade work to save PCB real estate and make playtime easier?

Has anyone developed artwork for the Plus board?

Figuring on:
- Fully socketed board?
- Short stroked SE style bayonet lug mobo installation to make crazy tall upgrade fitment easier than in SE.

Thoughts?

 

[-SE40-]

Ive got one Mac plus, and keeping it original…..for now….at least.
But looking forward to see what youve got cooking!

 

[max1zzz]

Might a 16bit, high capacity ROM upgrade work to save PCB real estate and make playtime easier?

Has anyone developed artwork for the Plus board?

I have repro plus boards, includeing one with a Rominator built in (Which I got PCB's for in January and still need to test!)

Really need to get around to posting those designs on github.....

 

[-SE40-]

@max1zzz , any pictures to share?
Looking forward to see more!

I need a spare/donor plus board now

 

[Trash80toG4]

I have repro plus boards . . .

Forgot all about those! How hard would it be to dumb that design down to 128K/512K status for playtime?

Working assumption here is that the less than Plus Compacts are thin on the ground and a bit too precious to hack. A Plus isn't nearly so hard to find and dedicating one for rechambered fun rather than reloading it in stock form should be an acceptable repurpose by reuse
conservation strategy for the hobby? Again, stock 128K/512K/512Ke Compacts are rare, expensive and should be conserved as is the way I see things?

edit: the DIP RAM adapter board plunked onto your SIMM thruholes mentioned above should work for expansion board fitment and 256K KeyChain SIMMs throttled down at the board level would be easily done I think?

 

[max1zzz]

@max1zzz , any pictures to share?
Looking forward to see more!

I need a spare/donor plus board now

There are a few pictures in this thread: https://68kmla.org/bb/index.php?threads/reverse-engineering-the-macintosh-plus-pcb.38414/

I'll post some more up to date pictures of the ROM-inated board once I have actually tested it..... Need to go pull the 512K out the loft so I can test it (Oh, and clear enough space on my desk to be able to put the 512k down somewhere!)

Forgot all about those! How hard would it be to dumb that design down to 128K/512K status for playtime?

With the current design it's a right pain, the current board design is just a tracing in sprint and as sprint dose not define electrical connections it is not fun to make major changes in! Redrawing the board in a morden CAD package with a linked schematic is on my list of things to do

 

[retr01]

So, maybe you guys can add two more lines from the 68000 so it has 24-bit addressing? Bodge wires, and let's show that the future Plus and current SE Reloaded boards can have two more lines from the 68000 in the gerbers!

We can prove how idiotic Apple was back in the day for only connecting 22 address lines from the 68000.

Apple has many things they will never apologize to the customers, especially from their dark parts of history.