Reverse Engineering the Macintosh LC Logicboard

[max1zzz]

With my Plus PCB's something along quite nicely (And by that I mean I'm refreshing JLCPCB's order page every 4 minutes to see how production is getting on) I decided to look at what to work on next (Something that actually needs reproducing!) and settled on the LC series, battery damage is common among these models and they also happen to be my favorite form factor of classic mac

I intend to work my way through the hole pizza box LC series in time but this thread is about the LC 1

I also happened to have a board that has been sitting doing nothing for the last 6 or so years, This board to be exact:


I was a little reluctant to use this board at first as it dose actually work (Or at least it did last time I used it 6 or so years ago!) but as I say it hasn't been doing anything so I might as well put it to good use. At least I will know if the repro doesn't work it is issue with my board and not the donor chips.

Step one is to strip to board of through hole components:

I was quite amazed at how much cap gunk was under various connectors, I thought I had cleaned the board pretty well when I recapped it!

Step 3 (coming soon!) will be stripping the surface mount components and scanning the board in.

Having examined the board fairly closely I'm pretty sure it is only 4 layers, I don't see any traces disappearing into the board however I will know this for sure once it has been scanned in.

 

[joshc]

Super excited about this, and so glad you are brave enough to start these projects. Watching this thread.

 

[chelseayr]

I'm curious too! had been tracking the compact macintosh board before but this one perhaps is more interesting to me due to separate monitor etc

on a side note tho: did the entire lc&rebranded board (I still can't get over that a 475 and 605 are just one gestalt jumper apart hm?) basically share the same pds bus compatibility correct?

 

[max1zzz]

Thanks guys

on a side note tho: did the entire lc&rebranded board (I still can't get over that a 475 and 605 are just one gestalt jumper apart hm?) basically share the same pds bus compatibility correct?

I believe all LC PDS cards are forward compatible, however the III and 475 have a few extra pins on the PDS connector so cards designed for them are probably not backward compatible. That said I haven't personally seen a card which uses the extra pins

 

[max1zzz]

And after 2 days step 2 is complete:

Tomorrow the PCB wil be scanned and the actual reverse engineering can commence!

 

[CC_333]

Tomorrow the PCB wil be scanned and the actual reverse engineering can commence!

Has this happened yet?

c

 

[max1zzz]

Has this happened yet?

Yep, the board has been scanned and I have started laying it out (all the top side component placement is done, in yet to start on the bottom side or the traces) but I received my plus boards a few days ago so have been busy troubleshooting them. Work will recommence when I figure out why I can't get the plus boards to work!

 

[max1zzz]

With the Plus Board now booting it's time to turn my attention back to the LC:

This might take a while!

 

[olePigeon]

Thanks guys

I believe all LC PDS cards are forward compatible, however the III and 475 have a few extra pins on the PDS connector so cards designed for them are probably not backward compatible. That said I haven't personally seen a card which uses the extra pins

The Sonnet Presto Plus accelerator will take advantage of a 32-bit PDS slot while, but still maintains compatibility with 16-bit PDS slots. However, it may be unique amongst LC PDS cards. I don't know of any other cards that can do that, but I've also never seen other LC III compatible accelerators or video cards. Would be interesting to catalog.

 

[joshc]

but I've also never seen other LC III compatible accelerators

Daystar had an adapter for the LC I/II/III that worked with their universal powercache 030. I've got one in my LC II, not tried it in an LC III, perhaps that used a different adapter, I'm not sure actually.

 

[DracheMitch]

The Macintosh LC would have been a pretty good computer had Apple not put it on a 16-bit bus.

 

[max1zzz]

Top side is now more or less done copper wise:

I still have the silkscreen to do but I'm going to get the bottom copper done first and then do a little sanity checking just to make sure there isn't anything suggesting there are any inner signal layers (I'm 99% sure there are some audio signals in the inner layer's but still haven't seen anything to suggest this is a general trend (AKA i'm still 99% sure this is only a 4 layer board)) before I do the silkscreen

 

[max1zzz]

Well that came together much quicker than I expected:

Now for the bit I haven't been looking foward to - the planes. It's not quite as simple as the older macs on this one, I can see there is a seprate plane for the IO connector as wit the older macs, but there also looks to be a split in one plane under the SWIM, and also maybe one under the video DAC. I will rpaobley sand this board tomorrow so I can be sure where the splits are...

 

[max1zzz]

And after a little tweaking to get the board to pass DRC it has now been sent off to JLCPCB for manufacture

The planes ended up not being too bad in the end, I managed to figure them out with just a bright touch and didn't have to sand the board. Also despite what I said a couple of posts back I didn't find any evidence of traces on the inner layers in the audio circuit.

Now I just have to wait for the darn things to be produced!

 

[paws]

Amazing work! Fingers crossed

The LC was our first family computer. I wonder where I'd been without it.

 

[mattsoft]

Wow, that was fast! Hopefully your first build won't have too many issues. I love the LC form factor as well and it's great to see these projects. Eagerly watching this.

 

[max1zzz]

Amazing work! Fingers crossed

The LC was our first family computer. I wonder where I'd been without it.

Wow, that was fast! Hopefully your first build won't have too many issues. I love the LC form factor as well and it's great to see these projects. Eagerly watching this.

Thanks

I'm pleased to say the boards have been shipped, estimated delivery is currently Wed/Thurs

 

[ajacocks]

I'll be interested to see the result of your work. The other challenge with the LC is that the cases are quite afflicted with brittle plastic, so we may need @maceffects to make new cases for them.

- Alex

 

[max1zzz]

I'll be interested to see the result of your work. The other challenge with the LC is that the cases are quite afflicted with brittle plastic, so we may need @maceffects to make new cases for them.

- Alex

So will I! tracking says the boards have made it to the UK so fingers crossed I might have the boards in hand tomorrow

Now that would be cool! I'm already planning to "build" a LC with as few original parts as possible (when / if I get these boards working) so a clear case would be great

 

[mattsoft]

A clear LC case would be very cool for sure. In your OP, you mentioned eventually working your way through the whole LC series. Curious if you plan to actually remake each model, or make some sort of "new hybrid LC" with features you like/want? Looking forward to your tests!