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Reverse Engineering the Macintosh SE PCB & Custom Chips for 1:1 reproduction


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Bolle, seeing your photos truly makes one see just how much damage battery acid causes, and just how damn near impossible it would be to repair such damage externally. Alternatively, however, if you guys scan this stuff in at each layer and make a diagram of what goes where, then the poor soul looking for the other end of a rotted trace actually will have a shot of bypassing it if he knows where the heck the other end is.

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Looking pretty good, with a few more photos someone would be able to run and do another PCB layout for the Macintosh SE/30 main logic board!  No need to wait around for the Macintosh SE boards to be finished.  Mentioning that, it would also be really helpful for making improvements to the redrawn Macintosh SE/30 schematics.  I noted elsewhere in this forum I started making improvements to fix some of the errors pointed out in the previous versions.

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On 8/26/2020 at 5:08 AM, Bolle said:

Had some time to grind away at one of my spare boards:

 

hTaw2ka.jpg

 

 

Going all the way down to the inner layers is going to be an absolute pain in the back.

I'll need to stock up on wheels for my grinder first.

Also it looks like the additional signaling two layers are right in the middle of the boards hidden under yet another set of VCC/GND plane layers.

 

 

Yea, I know. You almost need a milling machine. Like what they use for doing engine heads. If you know the layer depths, you could program the machine and setup a routing bit and vacuum nozzle head and let it rip. 

Edited by techknight
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Getting the board stuck down evenly would be a challenge though.

I do have a DIY-hack CNC mill and in theory the step size should be accurate enough to take off a layer. I guess it’s worth a try. I have enough dead boards here to play around.

In the end careful grinding might be the best option though I think.

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If you want to get a look at the inside layers of a PCB, you *can* use a small CNC mill with a small step size. This is probably the best example of that:

https://www.youtube.com/watch?v=iV4LJX1HdPk

 

However, there's a significant drawback going the CNC route if you don't have it perfectly flat. Half of the board will have the traces you're interested in, while the other half will cut too deep or too shallow. There's a lot of fixturing needed for this project.

 

I have heard of people going to a machine shop and using a surface grinder which would be a very good option if you could bond the PCB to a flat piece of steel (for the magnetic clamping). Alternatively, you could also find a machine shop with a _huge_ lapping machine. That would give you the ability to cut perfectly perpendicular through the plane of the PCB.

 

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SE/30 stuff, i'll break out into a separate thread, so we can concentrate on the SE/00 board here - sorry if i've been quiet, been enjoying a few days 'staycation', visiting friends etc. I'm back home tomorrow - so will get PCB's shipped out on Monday. 

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I guess this is as good as it gets... oh boy what a mess.

At least you can see both signal layers so I don't have to bother and get to the other side as well.

 

IMG_4246.thumb.jpg.0581ebbc773a5fbca6ad60c6b50c9d68.jpg

 

Damaged some traces but together with the schematics it should be easy to reconstruct those.

Edited by Bolle
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I am back from a week long staycation, and I have to say the new boards look even more amazing than the first batch did! So far the rear i/o power seems good and the GND and +5v for the 68000 and 74ACT257's is now there, along with the correct GND and +5v for the floppy and scsi, now... Just need to build one this week - they look amazing with new SIMM sockets, too! 

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....and this batch of boards is dead, too. I'm pissed off right now. The inner copper layers of the rear I/O are bridged. I've checked the files i sent and there's nothing there that can cause it. +5v and GND are bridged somewhere. Even with no components, it's bridged. 

 

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That's really unfortunate. Could one of the vias have caused it, or maybe one of the larger lugs at the rear of the board? Maybe if you have a sensitive tone generator and pickup you could potentially trace out the current flow to try to find where it connects or at least narrow your search a bit.

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I'm looking over the board at serious magnification - DRC checks, test pads show no components bridging - it's a manufacturing issue. Nothing is connecting anything incorrectly. If it were a component, that'd be understandable, but this is a board level defect with the internal layers. If you cut the bridge connecting the ground planes, the rest of the board has no issues, its just the rear I/O - i'm going to totally re-do the cutout areas, just in case, and make them intersect stuff. I may relocate some of the filters by 39.6875uM just to make them clear the 'split' just right. 

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Where did you have them fabbed? I never had any actual fabrication defects ever.

All boards go through electrical testing (at least at JLCPCB where I usually order my boards) so it really shouldn't happen at all.

 

You could try to connect a bench power supply and run a whole lot of power through the board to see where it starts to turn black to find out where the short is.

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