Logic Board - Macintosh Classic Reloaded

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Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
macclassicboard-final-rev12-release.jpg

As with the Macintosh SE, many Classic's have died because of Apple's short sighted decision to add a battery to the board - and unfortunately a particularly explosive one at that! This will inevitably pop and causes a horrific amount of damage.

Thankfully, because i've done this before, with the Macintosh SE, I decided to make a near 1:1 reproduction of the board, using Sprint Layout v6.0 again.

The Maxell batteries fitted to most classics, when they explode, will eat away at the component legs, tracks and via's if the battery electrolyte is left too long. Luckily almost all the other parts can be replaced with modern equivalents.

In the Macintosh Classic, the battery is placed in the bottom left hand corner of the board, underneath the RTC chip and to the left of the CPU. Mostly the damage is confined to this area, but if the system has been left a long time, you may discover the damage reaching beyond the SND chip (which is vital for generating the /RESET) functionality for the CPU and the board is essentially wrecked at this point.

Unlike the Macintosh SE, the PLCC versions of the SND and the RTC chip are not readily available and in the event of a total loss, will have to be salvaged from machines of a similar vintage.

The Macintosh II, IIx, IIfx, IIcx, IIci and IIsi all use the same SND and RTC chips - so if you have a destroyed/non-working board, you can salvage them from there.

As with the Macintosh SE board - there are other components than the custom chips that should be salvaged when possible, the 6-pin inductors/ferrite beads, the reset & programmers switch, RAMexpansion connector and headphone jack and try, if you can, to save the R/C network filters if possible, as these can be expensive to replace (sometimes £4 to £6 each!) Last but not least the DB-19 external Floppy connector, assuming the shell and pins haven't been eaten away by rust/battery electrolyte.

While it is possible to source some of the Apple custom IC's from resellers and chinese inventory warehouses, the supply cannot be guaranteed, so it is imperative that as many of the custom IC's are salvaged.

These boards aren't quite enough to build a new Macintosh SE from scratch (maybe one day, though!) - so you'll need to harvest a few parts from your donor board.
  • RAM Expansion Socket - 2 row, 44-pin connector - may be possible to substitute an IDC header.

  • DB19 Connector - Almost NLA, only really 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.

    NoS ones available from https://www.exxoshost.co.uk/atari/store2/ - search for DB19F ASCI PCB RA POST

  • Main 14-pin Molex - Molex P/N 39-28-1143 - Still available new - costs less than £2. Get a new one.

  • Inductors & Ferrite beads

  • Passives - REPLACE ALL - use high tolerance metal film resistors & Nichicon or Panasonic electrolytics.

  • AM26LS30's - NLA, only available as NoS or Reclaimed

  • AM26LS32's - Available new, but still worth reclaiming

  • MC3488A - NLA - replace with Texas Instruments SN75150

  • Rockwell 338-6523 - This is the 65C22N VIA, still available new as the W65C22S6TPLG-14

  • RTC Chip - Custom Chip - maybe possible to clone using a flex-PCB/ATTiny Chip

  • ADB Chip - Apple branded PIC16CR54 in a PLCC package - maybe possible to re-produce/clone

  • BBU Chip - Custom Chip - identical in pinout to the Macintosh SE

  • NCR5830/AM58C30 SCSI Chip - Reclaim, but if not possible, these can be purchased from Mouser, as ZiLOG still makes them under the part number Z53C8003VSG

  • SWIM Floppy Chip - Custom Chip - available NoS from UTSource

  • ROM Chip - Toshiba TC534200 MASK ROM - Reclaim & reuse, but these are the same pinout as 27C040
Project will be available on GitHub here: https://github.com/kr239/Macintosh-Classic-Reloaded - however, it's still a WIP, and i'll be selling a few boards to reclaim costs before posting the files publicly.
 
Last edited:

robin-fo

Tinkerer
Feb 17, 2022
85
43
18
Switzerland
Hello Kai, are your excellent replica boards already available somewhere? I have a Classic with severe battery damage which I’d like to 'reload'! Of course I’d be happy to populate it myself, so I just need the board.

Many thanks!
Robin
 

Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
Hello Kai, are your excellent replica boards already available somewhere? I have a Classic with severe battery damage which I’d like to 'reload'! Of course I’d be happy to populate it myself, so I just need the board.

Many thanks!
Robin
Hi! The Classic Reloaded is not available to the wider world quite yet - although, if you're based in the UK, I can send you a near final revision board that needs a trace cutting and two tiny bodge wires adding, then it works 100% fine - it's pre-populated with most of the passives on the bottom side, barring the inductors and ferrites.

If you'd prefer to wait, I've licensed the design for commercial use, to @MacEffects :)
 

mechsupreme

New Tinkerer
Apr 23, 2022
9
0
1
Hello, do you have a timeline of availability to USA, got a mac classic, pulled the board and the battery had destroyed the battery area, thanks
 

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Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
Hello, do you have a timeline of availability to USA, got a mac classic, pulled the board and the battery had destroyed the battery area, thanks
@MacEffects has the license, as with the Macintosh SE Reloaded, for board sales in the continental US - not sure of the timeline of production on their side though. If it's a while, i can do a small board run, with SMD pre-assembly done on the rear (barring the inductors)
 

Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
How much would the cost of board be? Rick
Well the boards generally come to around £35 and come with almost all the rear side passives populated. Then you move over most of your parts. I do have a p&p and BOM for the board, i'll post those on GitHub soon.

@MacEffects has the license for production, just a matter of when/if it goes on sale through the store :)
 

mechsupreme

New Tinkerer
Apr 23, 2022
9
0
1
Well the boards generally come to around £35 and come with almost all the rear side passives populated. Then you move over most of your parts. I do have a p&p and BOM for the board, i'll post those on GitHub soon.

@MacEffects has the license for production, just a matter of when/if it goes on sale through the store :)
U sir are a lifesaver, let me know where to send payment Rick
 

mechsupreme

New Tinkerer
Apr 23, 2022
9
0
1
What i should have asked is, would it be possible to do a small run and be able to purchase one? Rick
 

biho

New Tinkerer
May 17, 2022
3
1
1
hi, i have a strong corroded classic board and would like to fix all broken lanes with fly wires. would you also upload a BRB file that could be opened with openboardview so i could see where all the connections are going?
btw.
great work with the pcbs, that helped me a lot. on my board most of the traces are gone in the area of the battery...

i created a fork of Kai Roninsons pcb plans on github containing a photoshop file with every pin and trace in a single layer

 
Last edited:
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Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
hi, i have a strong corroded classic board and would like to fix all broken lanes with fly wires. would you also upload a BRB file that could be opened with openboardview so i could see where all the connections are going?
btw.
great work with the pcbs, that helped me a lot. on my board most of the traces are gone in the area of the battery...
Unfortunately, i don't have a board view, as such, it was created with Sprint Layout and currently it's not been released as Open Source (yet - it is planned this year, though).
 

biho

New Tinkerer
May 17, 2022
3
1
1
Unfortunately, i don't have a board view, as such, it was created with Sprint Layout and currently it's not been released as Open Source (yet - it is planned this year, though).
thank you for the reply. i hope its ok for you that i created a fork and inserted an photoshop version with the traces on single highlighted layers to make measuring of continuity easier 😀
 

Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
996
1
1,030
93
41
Worthing, UK
thank you for the reply. i hope its ok for you that i created a fork and inserted an photoshop version with the traces on single highlighted layers to make measuring of continuity easier 😀

Not at all! Don't worry, it will be released on github as the gerbers and the sprint layout this year - just gonna recoup some costs first :)