Apple PCB 820-0086-C

MacRedux

Reimaging of the original Macintosh 128k logic board 820-0086-C.

Introduction

This project is a re-implementation of a Macintosh 128k logic board. From this, I hope to derive the 128k/512k hybrid board. Primarily, I expect these would be used to replace an original logic board that has been damaged. There are several components that are generally "unobtanium" without harvesting from another board. These parts include the six PLDs (of which only 2 or 3 may have been decoded per some Google searching), the IWM (disk drive controller), the RTC chip (although a clone seems to have been made by someone), three RC dampers, and the external floppy connector (a custom 19-pin connector that looks like it used the DB13W3 shell size). The DB19F was also used on the //gs, Amiga, and NeXT machines, among others. You can still occasionally find them on eBay. I purchased 2 just to have them for measurements.

Project Status

The board has been fully test plotted but has not been sent to manufacturing. I was able to purchase an original board, so most of the critical measurements have been validated. However, there still may be minor differences between the original and this version, mostly relating to the rear connectors, the RJ11 jack, and the pushbutton switches on the side.

Versions

• v1.0-001: Initial prototype based on original schematic.

Known Bugs/Issues

• The board still contains several DRC errors, mostly due to components encroaching on eachother ("porch violations"). There will likely be permanent encroachments given how dense the board is in certain areas.

• Certain components (like the push buttons, keyboard connector, and audio jack) are being replaced with what I think are current equivalents, so further adjustments could be needed for those so that they are positioned properly on the planar.

• As of now, the PALs have not been fully decoded. The archive includes a text file with some notes I've collected on the topic from various places on the Net.