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Reverse Engineering the Macintosh Plus PCB

max1zzz

Well-known member
Like many of us I have been following Kai and Bolle's Progress in reproducing various Macintosh PCB's I thought it might be fun to have a go myself!
I ended up settling on the Macintosh Plus (Even though there is no real need for Plus reproductions) since it is a fairly simple PCB (2 signal layers on the outside, power and ground on the inner layers and all through hole components) and was easy to get hold of. I figured if it went well I might move on to something more in need of reproducing :)

I'm sure we are all pretty familiar with now, The board gets stripped and scanned:
index.php


Rather annoyingly the was just a few mm bigger than the bed of my scanner which would result a small amount of one side of the board being cut off from the scan this would have been OK except it also resulted in the board not sitting flat so half the board was out of focus so I ended up having to do two scans of each side and merge them approximately in the middle

The scans are then loaded into Sprint Layout and traced:
Plus_Sprint.PNG
It took about a week of drawing traces for about 2 - 3 hours each evening to get to here. I'm pretty happy with the way it is looking, it's not exactly a 1:1 repo but it is fairly close (Some traces take slightly differen't routes and the silkscreen has been altered to have component values. It is however close enough if you where working on a original board you could use the layout to work out where things go)

And that's pretty much it for now, The next step will be sending the boards off to JLCPCB for manufacture!
 

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Juror22

Well-known member
Nicely done! Thanks for sharing your process and results, I definitely need to start working with these tools as well.
 

max1zzz

Well-known member
Thanks guys :) I'll be sending the boards off to JLCPCB tonight. Just finishing off another board I want to send off with them.

@Kai Robinson I used the "automatic ground plane" feature and then drew a cutout area for the split. I found it a little counter intuitive (I'm used to drawing the copper area) but it seems to have worked well enough
 

uliwitness

Active member
Say, I'm not sure if you folks are familiar with the Commander X16? It's an effort to basically build a C64 clone that can be used today (with HDMI displays etc.) and is simplified a little. Useful for e.g. teaching computing basics.

I'm wondering, could these PCBs be used for a project like that? Could one build a new 68k Mac, today, maybe with a few modifications to support more readily available keyboards, displays etc.? I'm assuming the answer is "sort of but no", as one would have to change the PCB to substitute different chips, but it sounds like it would be a cool project.

I know there are extension cards containing entire Raspberry Pis and FPGAs that people have used to create chips that behave like old C64 or Amiga chips/peripherals but will actually get you on the internet, handle talking to USB devices and SD cards.

I guess the biggest problem with a Mac, as always, would be the ROMs?

I'm sadly pretty clueless when it comes to hardware, but I do have a copy of CodeWarrior lying around here and would happily help out with software for such a project.

Just dreaming here,
-- Uli
 

Kai Robinson

Well-known member
@uliwitness it's not outside the realm of possibility - there are 4 chips on the SE that haven't been reverse engineered (yet!):

The BBU (the main glue logic)
The ADB MCU (although that's 'in progress')
The SWIM/IWM floppy controller (this is fairly well documented, should someone wish to take that challenge on)
The Sony SND Chip

On the Plus, most of the glue logic is handled by PAL/HAL devices - and they can be a pain to reverse engineer, especially if they're registerered parts. But not impossible. Some already have been reversed - but theres enough still unknown about them.

There is still the matter of the IWM as well, and the Sony SND Chip - although there seems to be enough of the latter in stock, new, to build at least 50 or 60 new machines from scratch.

Then it'd just be the legalities surrounding the ROM - as that's still copyright by Apple.
 

markyb86

Well-known member
I'm wondering, could these PCBs be used for a project like that? Could one build a new 68k Mac, today, maybe with a few modifications to support more readily available keyboards, displays etc.?
Doesn't seem like there is much room for additions on the board layout, but I'd imagine baking in a modified mac plus> PS/2 keyboard adapter (http://www.synack.net/~bbraun/mackbd/index.html thanks to @bbraun) would be a welcome addition!
 

uliwitness

Active member
@Kai Robinson Oh that would be cool.

Though I guess it might be easier to just use all modern hardware, with maybe a patch to the ROMs or so to make it look like original hardware for anyone using system API. I mean, a Raspberry Pi these days is probably fast enough to emulate a Mac Plus at real-time speed. So I see why this hasn't been done yet.

That said, a friend recently pointed out to me that Apollo's Vampire V4 and the MiSTer (680x0 Amiga and Atari ST clones) can supposedly also be made to run MacOS if you install some extras (one of which I suppose would be a ROM). I'll have to investigate some more, haven't really found anything concrete on how one would do that.

Still, if any of you main board PCB makers is looking for their next project ... :)

I'll definitely be looking into maybe contributing my software skills to something like that.
 

max1zzz

Well-known member
Doesn't seem like there is much room for additions on the board layout, but I'd imagine baking in a modified mac plus> PS/2 keyboard adapter (http://www.synack.net/~bbraun/mackbd/index.html thanks to @bbraun) would be a welcome addition
That's a interesting thought I wonder if I could build a little PCB to replace the keyboard connector with one of those adapters intergrated..... The keyboard connector is not they easiest part to get (I think I found mouser or digikey carry it but no one in the UK did) so this wouldn't be a bad thing to do.

I think there would be enough space to build the adapter directly onto the Plus's PCB if you put the micro directly onto the logicboard rather than using the discovery board, it's something I might think about once I have the boards and know they work :)
 

mg.man

Well-known member
Doesn't seem like there is much room for additions...
Well... if we're talking possibilities... what about elbowing surrounding components a bit and squeezing in the original ROM-inator circuitry [https://www.bigmessowires.com/mac-rom-inator/]?... It would mean larger "ROM" sockets - but having an on-board "boot" drive would be cool!! Also... there were tools for the original ROM-inator that allowed you to update it in-circuit! ...something that's not possible with the ROM-inator II.
 

max1zzz

Well-known member
if we're talking possibilities... what about elbowing surrounding components a bit and squeezing in the original ROM-inator circuitry
Should be possible, the main issue would be routeing the few extra data lines needed form the CPU as the board is fairly crammed track wise in that spot
...or what about the PLCC type?
Space wise it would be easier but would probably easier (Two AM29F040's would easily fit in the space of one of the current ROM chips) but it may mean shifting more traces around than using the DIP variants

hmm..... now I'm trying to resist the urge to start modifying the board before I even know if the original design works :)
 

max1zzz

Well-known member
Space wise I might actually be tempted to go with the TSOP chip, In my opinion TSOP chips are actually easier to solder than PLCC chips, but socket options are more limited...
 

max1zzz

Well-known member
PCB's are finally here!
IMG_1576.jpg

Sadly I only have 3 as two apparently failed QC after production....but at least the credit I know have with JLCPCB will pay for a good chunk of either the modified plus boards or the LC boards I'm working on :)

Assembly and testing will commence shortly!
 

max1zzz

Well-known member
Oooo... red... very stylish! :cool:
Yeah they look really good in red :) I initially intended to use red as colour for prototype boards only, but they look so good in red I might just stick with it for any future runs

And assembly is progressing quickly, just waiting for some 24pin 0.3" sockets to arrive (as CPC sent me the wrong ones and my replacements form eBay are yet to turn up...) and then I should be ready to test

IMG_1579.jpg
 

Byrd

Well-known member
Board looks magnificent - the red PCB really gives it that prototype appearance :)

Must drag out my Mac Plus soon; I've got this oddball Novy 020 early accelerator I've got to test on it, but will need a socketed 68000 I think.
 
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