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

[techknight]

I just checked the test points for voltages - instead of reading +5v, it's reading +7.5v!!! 

I think my analog board has potentially killed some chips...

Yikes! yea that spells death to semiconductors :-(

 

[Kai Robinson]

Well, most ttl has a bit of leeway, I'm hoping it hasn't taken out the BBU - everything else is expendable... 

Here's the result of a 20 second power on with a set of 256k simms :

 

[360alaska]

In case the problem actually is the board how you ever used one of these:



Maybe comparing your board to a stock board with a huntron will yield some clues?

 

[Kai Robinson]

An Oscilloscope is on the way - i do have a logic analyser - but i'll be damned if i can find a DIP64 IC test clip!

 

[Kai Robinson]

Knocked up an adaptor for the SE ROM's - i have a funny feeling mine aren't making proper contact in the sockets, the legs, even cleaned, are tarnished...the ones from the spare board i have...well i tried removing them and the legs stayed in the sockets, so i now have a load of icosaoctaplegic Mask ROM's

I have 10 prototype boards in a panel with ENIG and V-Scored edges on the way from PCBWay (Making use of the $100 or so commission i earned from the Amiga stuff i've done in the past) so if anyone wants to test these, i have 9 available. 

 

[quorten]

Losing legs from a ROM, ouch.  The price of those DIP64 IC test clips just keeps going up and up, but they're at least out there...

https://www.digikey.com/en/products/detail/3m/923739-64/12091

Another note, I also looked deeper into the Unitron's logic equations and tried coding them up in Verilog mainly to run a simulation that I could compare the BBU's waveforms with.  Indeed this was helpful in answering a few last questions, though it did feel a bit like a "distraction" from the BBU.  One interesting note, though, I found the Unitron's C3.7M clock is generated by inserting two C16M cycle waits every eight C4M cycles, rather than one C16M cycle wait every four C4M cycles.  It could be that the original Macintosh actually used this behavior, but of course there's no need to copy the inferior approach for the BBU.

 

[cheesestraws]

Knocked up an adaptor for the SE ROM's - i have a funny feeling mine aren't making proper contact in the sockets, the legs, even cleaned, are tarnished...the ones from the spare board i have...well i tried removing them and the legs stayed in the sockets, so i now have a load of icosaoctaplegic Mask ROM's

If you want a spare "stock" set I can drop some in the post to you.

 

[Kai Robinson]

@cheesestraws Oooh, i may have to take you up on that - i basically need a whole other SE board, so i have some duplicate customs for testing...

 

[cheesestraws]

i basically need a whole other SE board, so i have some duplicate customs for testing...

We can sort this.  I'll send you one of my spares.

 

[Kai Robinson]

I have a funny feeling that it's the oscillator, not making good contact in the socket...this weekend i'll desolder the socket and hard solder the oscillator in, see if that makes a difference. 

 

[Kai Robinson]

OK - work has been manic (office move of the whole IT store and comms room to new building) and i've yet to have enough time (or space) to sit down and solder anything. I have, however, come up with a few little bits like the ROM adapter, and now, i have this - behold, the PLCC84 breakout adapter! Desolder the BBU socket, solder this in its place, then solder a new socket to that board - voila, signal breakout!

@quorten would this be of use to you in your BBU reverse engineering? 

 

[quorten]

@Kai Robinson Possibly... one thing that makes me think about is setting up some sort of independent "hardware test fixture" like I've designed (but haven't yet tested) for the RTC chip, but for the BBU I'm still tweaking the logic and setting up the simulation test.  Things have been exciting for me work-wise, I started a new job last week.

 

[demik]

However, thanks to Rob Taylor, the man responsible for getting me into the reverse engineering in the first place, I now have a new toy to play with! Finally a proper PAL dumper! Will get a ZIF socket but i have everything else I need - anyone else want one?

View attachment 38575

I'm reversing a MacSNAP SCSI ATM and would love one of these. Are they still avaible ?

 

[SlickClick]

What Speed are you running the system bus at..?
I noticed the CPU you are using is the later version which can run at high speeds... The system is designed at 7-8Mhz bus speed...
When you up the System Bus Speed it gets wonky with the Analog Video Circuity; if you're running a high Clock Speed that may be part of your issue as well...

The Higher Voltage of 7.5v might only effect the smaller 3.3v circuit as that would be at the top of the tolerance levels (ie Double Voltage)...
Check that your RAM is still good... 

 

[quorten]

Hello @SlickClick, welcome!  In this case the master clock should be ~16MHz and the BBU divides that down to the ~8MHz CPU clock.  Have you actually run a Macintosh SE with a higher speed master clock?  I would have suspected that higher master clock speeds wouldn't work at all without a BBU mod, but if they do in fact work by simply overdriving all the generated clock frequencies, that would be good to know for the BBU replica design.

The Macintosh SE MLB doesn't have a 3.3V power circuit to my knowledge, it should all be 5V chips on there, assuming that vintage RAM is used.

 

[Kai Robinson]

@SlickClick 7.83Mhz is the Bus speed in the system. The CPU is an L10 - mostly because it's a nice, gold top ceramic CPU, no other reason

 

[Scott Squires]

OK, I've been out of the 68k loop for a couple of years. Now look what is going on! Very nice!

The Mac SE overall is the most reliable of the compact Macs. (Perhaps even most reliable of any Mac.) Through-hole parts, no leaky caps, the batteries don't often explode (mostly I have seen the Varta and Tadiran batteries in SEs, nigh a Maxwell to be found). The real Mac that needs replacement PCBs is the SE/30. I alone have at least 4 of those with trace rot beyond salvage. That one's more complicated though, so it makes a lot of sense to start with the SE.

I need to learn Verilog so I can help with the custom chip side of things. I've been saying that for 3 years...

 

[rplacd]

I need to learn Verilog so I can help with the custom chip side of things. I've been saying that for 3 years...

Same! This thread has inspired me to take a good crack at learning digital design. As an early Christmas gift I bought myself an FPGA trainer board and a textbook.

 

[quorten]

I need to learn Verilog so I can help with the custom chip side of things. I've been saying that for 3 years...

What I've been thinking to myself about my knowledge of Verilog... I needed a few more classes to fill up my computer science degree electives and the relevant classes seemed like something that wasn't too over-hyped or overly specialized.  Probably not going to use it at my main job any time too soon but it sure is fun for side projects.  Ha ha ha!

 

[Hiro256]

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 - IMPOSSIBLE TO GET - desoldering these needs HEAT as there are a lot of connections to the ground plane. Pre-heat the joints, maybe add a dab of proper Kester 63/37 eutectic LEADED solder (none of that RoHS crap), flood with flux. 
  
• 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
  
• ADB Chip - Apple branded PIC16CR54 - maybe possible to re-produce/clone
  
• GLU Chip - Apple branded PAL16L8 - maybe possible to re-produce/clone
  
• BBE 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
  
• DB19 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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Oh I see, the SIMM connectors for memory still used in Japan . You can find most of the parts on the list actually, but probably better to put everything into one FPGA.

https://www.mouser.com/Connectors/Memory-Connectors/Memory-Socket-Connectors/SIMM-Connectors/_/N-axja3