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

Tool suggestions, soldering tips, general useful electronics knowhow.
Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 5:59 pm

If i may, i'd like to crosspost my project from 68k MLA forums, if that's ok?

So - as the title explains, this is designed to save as many Mac SE's as possible. So many have died thanks to the stupid PRAM battery on the board, and with the SE being a 2-layer PCB with just through hole components, it's actually one of the easiest to save. So - how do you reproduce a PCB?

First, get a Mac SE PCB - in my case a 'dead' board from eBay for €29 - thanks, random spanish man!

Then, you get to work desoldering. Literally EVERYTHING. Not a single component must remain! However, 30 year old solder and my ZD-915 desoldering station caused a handful of through holes to just pull out of the board, or some traces would come up with it. I found that pre-heating the joint, with a little flux (AmTech RMA-223), would make the solder melt a lot cleaner when you use the ZD-915 desoldering gun. You must use a lot of heat, on these boards. For those joints that have been corroded, you must flood the area with flux, heat from both sides, then try and move the pin using a soldering iron (i find 420 degrees C suitable, with a standard flat tip) before trying to use the desoldering gun. Sometimes it won't always come out of the joint, in which case reflood with flux, and attack it with desolder braid. I use 2.0mm GootWick, which is fantastic stuff (thanks to Louis Rossmann for the recommendation).

As part of this process, I made a list of the parts that you need to save, and the ones that you can ditch. Obviously, all the custom Apple ones are a must - the rest are either still available, or are available as new-old-stock or pulls.

So - here's what you need to save:

SIMM Sockets - If you can, salvage, however you can get brand new ones with metal clips from peconnectors.com
PDS Socket - Amphenol/AMP/AVX DIN-41612 3-row, 96-pin connector (Style-C) - Available new, but still worth reclaiming as sifting through the minute variations of parts is an arse...
Inductors - probably easy enough to get new ones, but ehhh, they don't really break, and they fit fine.
AM26LS30's - NLA, only available as NoS or Reclaimed
AM26LS32's - Available new, but still worth reclaiming
MC3488A - NLA, only available as NoS or Reclaimed
RTC Chip - Custom Chip - maybe possible to clone using pin-compatible ATTiny85, or ATTiny87 in TSOP with an adapter
ADB Chip - Apple branded PIC16CR54 - maybe possible to re-produce/clone
GLU Chip - Apple branded HAL16L8 - maybe possible to re-produce/clone
BBU Chip - Custom Chip
NCR5830/AM58C30 SCSI Chip - NLA, only available as NoS or Reclaimed
WIM/SWIM Floppy Chip - Custom Chip
Hi & Lo ROM Chips - Toshiba TC531000CP MASK ROM's - Reclaim & reuse, but these are the same pinout as 27C512, but adds A16 in place of VPP pin - you can use 27C1001's on an adapter - doug brown made a similar setup with a built in ROM disk for the Mac Plus.
74LS245 - Available new, but still worth reclaiming - replace with CY74FCT245ATPC or CD74FCT245E
74F257 - Available new, but still worth reclaiming - replace with CD74ACT257E
DB19F Connector - NLA, only available as NoS or Reclaimed. These are a bastard to get out cause the lugs are soldered. I found that pre-heating the joint first, filled with flux, then pressing hard into the pad with the desoldering gun, waiting til you see the solder go molten, you can often schlorp out the majority of the solder and then tidy up with wick afterwards.
Passives - REPLACE ALL - use high tolerance metal film resistors & nichicon or panasonic electrolytics. Maybe try and save the PLCC Socket if you can. remove it cleanly - sometimes the pins pull out but they can be put back in if you're careful.

Once you've saved all those parts, it's time to get scanning! 800 to 1200dpi on your scanner. If your scanner bed cant quite fit the whole thing on, scan one side, then rotate 180 degrees, scan, flip the image, then you can merge the images in photoshop. My scanner clips about 5mm off, so i use this method.

There will be a part 2 to follow...but any questions so far?
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Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 6:48 pm

So let the desoldering commence!
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Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 6:57 pm

Once everything has been removed from the board, and after scanning @ 1200dpi, and some jiggery pokery in photoshop to merge the images, you should end up with something like this. These are low-res versions of the board, in time i'll pop up the full versions.
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So - now that the board scans have been done, it's a matter of adding them into Sprint Layout Editor as a background/template and then adding the components/pads, silkscreens, tracks and inner power planes.

Here you can see the board view so far, after 8 hours, and what i'm seeing in sprint.
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PhilC
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Re: Reverse Engineering the Macintosh SE PCB & Custom Chips for 1:1 reproduction

Post by PhilC » Tue Sep 15, 2020 7:38 pm

Thanks for sharing so far.

If you do want to upload the high res images of the board, you're probably best to upload them as a zip as the forum auto resizes image files otherwise :D
If it ain't broke, test it to Destruction.

Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:11 pm

It's okay - i don't mind resizing for the forum - you get the general idea at least!

Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:19 pm

After a busy week, i got a whole Mac SE that was well and truly buggered by the wrath of a maxell battery...

Still, the board being dead can still be very, very useful in reconstructing the ground and power planes - yes, it might look like a 2-layer board, but it is, in fact, a 4 layer board - with signals on top and bottom, and inner planes being +5v and GND. 12v is carried on surface traces 1mm wide.

Rather than sanding the layers, i'm manually testing each via and component with a 'loose end', seeing if they belong to the +5v or GND planes, and basically trying to line them up with the charcoal imprint of a schematic that exists - seriously, if anyone has a better version of that schematic, please, for the love of al that is scientific and factual, can someone SELL IT TO ME!
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Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:25 pm

It took a little while, but i managed to get the silkscreen done, and all the components labelled. I also tweaked the metal reinforcing points to proper solder pads, too and managed to properly split the power planes for rear I/O isolation through the inductors by the use of an exclusion zone.
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Literally every last pin checked*, every component given a proper value (so i can export a BOM), all ground and power planes checked, even against the charcoal rubbing schematic that's out there in the wild. I'm was ready to pull the trigger on a set of boards - who wants one of the test units to try and build/rescue an SE? If it doesn't work, it'd make a great wall piece and talking point, right? :lol:

Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:36 pm

* it was at this point i realised a large mistake. I'd forgotten to actually check the rear I/O for proper grounding on the connectors and lo and behold, i had forgotten. Unfortunately, i'd ordered a batch of 5 test boards first, before realising this mistake. What was also left out was the connections to the 74ACT257's and the 68000 itself in so far as power was concerned - i blame tired eyes!

When you're editing in sprint, after a while, it all looks like you're staring in a bag of neon bassets allsorts!

So once these boards are tested, if they work OK, then i'll put them up in a Tindie store to allow people to buy single boards off me, with a little markup so i can recoup the development costs of the board - after that, i'll release the Gerbers for all to make and move on to the SE/30, Classic or whatever else people want me to make next...just need two or three dead PCB's and a copy of the schematics and i'm all good to go ;)

Anyway, the batch of boards turned up. I got these manufactured at JLCPCB and it turns out, they do good work!
There's a few things i noticed such as tight holes on the PDS side of things...and the SIMM sockets, but other than that sockets fit fine! All holes seem to line up 1:1 as well.
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Yes, a little shoutout to @chucky on the back, it seemed only fair!

Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:38 pm

After an inspection of the boards, i can say the following: JLCPCB did a fantastic job, for the money.

The silkscreen on both layers is sharp and better quality than my previous efforts from PCBWay for sure.

Everything fits - although the holes in the prototype may be a *little* tight for reusing some old parts - thankfully most of the parts that need to be reused are to be socketed anyway, so not really too much of an issue - although the SIMM socket pads were default 1.4mm x 0.72mm, so i've made them and all the other DIP socketed parts a touch larger, at 1.6mm x 0.8mm to make for a better fit, especially if reusing parts.

The pads for the rear I/O, such as the ADB/Serial and the metal support bracket are a tight fit and i missed out excluding the pads on the underside from the solder mask, so i've already re-done the sockets from scratch to give a 0.25mm larger surface area (track width from 0.25mm to 0.50mm as they're 'drawn' and then infilled with an exclusion zone), as modern PCB's are very, very accurate and incredibly fine, compared to ones from the 1980's.

Now the biggest fear i had was mounting hole alignment. Fear not - for all the holes line up bang on! Literally, 1:1 is what i was aiming for, and i assumed i may be out by about 2-3mm in some places, but from the measurements, 1mm difference at best - In addition, all the rear IO ports are PERFECTLY ALIGNED with the back of the case!

Kai Robinson
Posts: 30
Joined: Wed Mar 13, 2019 12:01 am

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

Post by Kai Robinson » Tue Sep 15, 2020 8:44 pm

While i was waiting for the last batch of components to arrive (remember, i'd not caught the power/gnd issues at this point) i decided to take another run at the board in sprint again, to tidy up all the snag points i'd noted. I did a final revision of the silkscreen on both the front & back, adding in the original 1977 Apple logo as the original Mac SE board used (despite the fact that by then, Apple used the Apple Garamond font everywhere...which was...wierd.)

I've also changed the size of the via's to 0.8mm with an internal diameter of 0.4mm, and tented them by excluding them from the solder mask - should look much more professional compared to the prototypes.
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