Fully Working Amiga 1000 with 2MB Chip

[intric8]

Last night at the Seattle Commodore Computer Club something really remarkable happened. With some ingenuity and skillful talent by group member Christian, we modified then witnessed an original Amiga 1000 Rejuvenator crank up to 2mb of chip RAM!

For this to happen we needed two things (in addition to the Rejuvenator).

First and foremost we needed a highly coveted Fat Agnus found in the Amiga 3000: 8372AB (318069-03). I happened to have lucked into sourcing one last year early in 2018.

Secondly, we needed the RAM to support it. My Rejuvenator’s 8 RAM bays all utilized a very old and antiquated type of RAM not in production for probably twenty years or more. The original default [email protected] chips equal 1mb of total chip RAM. To reach 2mb totals, the needed chips are increased in size and staggered, thus only requiring 4 chips instead of 8.

Removing the old, original 128kb RAM chips. Very carefully...

The four new 256x4 DRAMs in DIP format mounted to adapter boards and installed into the original sockets.

Sourcing the old RAM is extremely unlikely. This is especially true if we want to try and build multiple boards in the future. Christian instead sourced a much more common DRAM chip in DIP format, which are much more plentiful and easily obtainable. To go this route, he had to solder the RAM to new adapter boards which required surface-mount soldering.

Going this route means regardless of future Agnus’ a user might have, the two types of RAM should be much more easily available - with the caveat that they would need to either solder their own adapters, or we create them pre-built. We’ll worry about logistics later - the great news is the RAM strategy WORKS and should no longer be a potential major roadblock.

In addition to the RAM issue being resolved we’re still left with the possibility of changing the 2mb Agnus to a more easily found A600 variety, but we’ll worry about that later.

Now that the schematics are getting close to completion we may very well be looking at printing some first-rev test boards in the next few months - which is amazing!

I took some pics of the new working RAM, in addition to my Amiga 1000 seeing it just fine. Enjoy.

(In case the numbers confuse, I'm running a 256kb front expansion as well as an 8mb MKL fast RAM board, thus the bonkers 10+mb totals).

[Christian]

Couple of minor corrections

The old DRAMs were eight 256Kx4 in DIP format. The new DRAMs are four 1Mx4 in SOJ format with an adapter board that converts them to DIP format.

[BloodyCactus]

so the rejuv is wired to use more address lines than what was on 256x4 drams and it just auto senses the dram address lines and fires ras+cas? thats handy

[A1-X1000]

awesome ! now I only need a Rejuvenator board

[nonarkitten]

While I think it's essential to clone the board as-is for initial testing and proof, I think two mods are essential before actual release -- the change from the rare-as-hens-teeth Amiga 3000 8372AB to the more common 8375 -- and the change to more modern 2MB of DRAM modules right on the PCB so we don't need little adapter boards. Other than that, I think it's perfect the way it is, and hopefully we don't lose the video slot -- that would be awesome if we can keep that for the A1000, even if I'm not sure I'd want to use it, but I might have to since the IndyECS is not compatible with the Vampire accelerator...

[intric8]

and hopefully we don't lose the video slot

I believe the board will have the ability for people to attach their own adapters, but we would not likely source the parts for that. There would just be a blank area on the board (with traces) where the vertical adapter could be soldered on by the tiny few who might want it. IIRC the Rejuvenator only supported two video cards that were available back in 1990/1991. It's not very practical for us to invest in that.

As long as the new boards work without the adapter being soldered on in (which it totally should) anyone else could take it upon themselves to try and build that out.

I really should do another update video. It's been a few months. We're as far as we can go until early 2019 where we will hopefully begin to build boards and test what we've got so far.

[joethezombie]

[...]the change from the rare-as-hens-teeth Amiga 3000 8372AB to the more common 8375 -- and the change to more modern 2MB of DRAM modules right on the PCB so we don't need little adapter boards.

Which version of the 8375 would be most appropriate to target, or are the pinouts for all 8375 the same?

And if anyone has a source or part number for the video connectors, let me know. It mentions in the Rejuvenator manual several options for pulling signals from the mainboard to increase compatibility with other boards, but they didn't go that route due to the complexity of wiring the end user would have to perform. It seems to be targeted mainly for the FlixerFixer.

[nonarkitten]

I really should do another update video. It's been a few months. We're as far as we can go until early 2019 where we will hopefully begin to build boards and test what we've got so far.

Has your team managed to decode and/or reverse engineer the GALs? Very much looking forward to an update, and while it pains me to have to wait for these things, it's nice that they don't all happen at once, otherwise I'd probably be bankrupt. Amiga is an expensive hobby.

[intric8]

Great question, and this project is definitely due for an update. I hope I can get one up in the next 1-2 weeks.

The PALs are still being worked out, and due to some life issues with one of the team member's we're probably looking at early 2019 to see if that work pans out.

[obitus1990]

I was thinking of buying some of those SOJ to DIP adapters to fully populate another old accelerator card, a Microbotics VXL-30 and its RAM board. Do the adapter PCBs block access to adjacent sockets? I ask because they do look quite large, and, I think the VXL-30 requires that RAM modules be placed in every socket, unlike the every other format this board allows for. Sorry to go off on a tangent from your thread, but, I'd really like to know that piece of information.