Macintosh Plus revival

Analog board troubleshooting.

Macintosh Repair & Upgrade Secrets.

Ports and pinouts.

December 1, 2021

First step was to take the computer apart, separate logic and analog boards, remove the CRT and diskette drive. This followed numerous how-to videos on YouTube with extra special care when handling the CRT high voltage!

A visual inspection revealed a few obvious issue pictured below, compared to information provided in the "Analog board troubleshooting" guide and the "Macintosh Repair & Upgrade Secrets" book.

Broken pin in anode connector to CRT.

Discoloration of glue on fly-back transformer that may indicate imminent failure.

Mains filter capacitor, C38, looks damaged by heat. Case is brittle and burnt.

December 3, 2021 Diskette drive disassembly and cleanup following Bruce at Branchus Creations.

December 11, 2021 Washed case and internal brackets with dish soap and warm water. Then thoroughly wiped down and dried all parts before assembling logic board and drive.

Next I'll tackle the analog board and figure out what to do with the display; fix or replace.

December 18, 2021 The problems on the logic board and the cost to fix them forced me to consider other option for reviving this Mac Plus. While I wanted to preserve as many of the original components I found it to be cost prohibitive. I was looking for alternatives and decided to remove the Analog board completely, use the RGB-to-HDMI solution with an LCD panel instead of the CRT, and power the system with a small ATX power supply I had lying around.

The first step was to check if the ATX supply would support to system and fit in the chassis.

I tested the power supply with a modified cable harness, fitted the setup in the original Mac Plus box, and relocated the speaker with a custom 3D printed holder.

December 26, 2021 My Mac came with no mouse nor keyboard. I plan to replace the mouse with a hacked serial (or PS2 mouse), and replace the keyboard with a PS2 keyboard + interface circuit to convert PS2 protocol to the Mac's serial protocol.

I had some time this past weekend to hack a serial mouse. There are several references on the web for such a hack, which is quite simple to do. The mouse needs to be a mechanical model with a steel roller-ball and optical encoders. I removed the quadrature-encoder-to-serial chip as well as some diodes and replaced the mouse serial cable with one that will eventually use a 9-pin DSUB connector into the back on the Mac's mouse port. I also tied all three mouse buttons in parallel and added a pull-up resistor.

Update (Feb 6,2022): When I connected the mouse to the Mac it turned out that the photo transistors don't have the capability to drive the Mac logic circuits. I added a small LM324 circuit, wired as a comparator, inside the mouse to shape and drive the signals. The diagram on the left shows how I connected one of the four photo-transistors. All four should be connected to the four op-amps.

February 6, 2022

I used this project documented on GitHub. I ordered PCBs at PCBWay and all components at Newark. The assembled circuit board and Raspberry Pi Zero stack are pictured on the left inside a custom 3D printed cradle.

This article has an implementation for both ATX power supply and RGBtoHDMI setup.

Combined with the hacked mouse I have a partially operational Mac!

February 12, 2022

I removed the battery holder, switch, and power socket from the analog board and attached them to the chassis. They are cabled to the ATX power supply with a disconnect plug in between.

The mains power socket is reinforced with two #4 screws.

February 26, 2022

The Mac Plus I have is also missing a keyboard. Like the mouse, I decided to build a simple interface with components I already had. The interface is a small AVR chip, ATtine85, that interfaces a PS2 keyboard to a Mac Plus serial protocol. The circuit is built on a perforated board and housed in a 3D printed box that is spray painted in black.

There are numerous ready-made solution, but I chose to reuse and modify code (GitHub) I already wrote and used in other projects like the PC-XT and Dragon 32 computers for the same purpose of interfacing a PS2 keyboard.

I now have functional keyboard and mouse for the Mac.

March 5, 2022

I removed the faulty analog board and with it the CRT, and replaced them with the RGB-to-HDMI setup. Now I can install an LCD panel as the display device.

The LCD panel dimensions are 9.7" (diagonal), and it has a resolution of 1024x768 pixels. This 4:3 aspect ratio and pixel count are a perfect match for the old Mac display. The pixel count is also a 2:1 ratio of the Mac's resolution, which allows the RGB-to-HDMI system to accurately scale the sampled video. The RGB-to-HDMI setup files are on GitHub.

The LCD is held in place by 3D printed "buttons". I don't plan to cover the space between the Mac's front panel and the LCD. The video HDMI output has overscan settings to resize the picture to fit the opening.

April 9, 2022

I bought a BlueSCSI kit and with a nice collection of images recommended on the BlueSCSI GitHub Wiki got a System 6.0.8 and a 7.0.1 up and running with games, a THINK C development environment, and a BASIC interpreter.

April 10, 2022

A serial link between the Mac Plus and a PC is a useful method to transfer files as well as use the serial link to connect the Mac Plus to a network.

The setup is simple, but requires building a suitable Null Model cable between the Mac 8-pin mini DIN serial connection (originally for a modem) and your PC. I found a cable with the right connectors at a local electronics shop and replace one end with a 9-pin DB9 connector for the PC side.

For file transfer I use ZTerm v1.0.1 and Minicom on the Linux PC, with a link setup for 57,600 BAUD 8N1 and hardware flow control enabled.

Now that file transfer works reliably I will try TCP/IP over serial link.

Coming soon ...

Now that file transfer works reliably I will try TCP/IP over serial link. Required software components on the Mac Plus include running System 6.0.8 as minimum with MacPPP 2.0.1 and MacTCP 2.0.6. Web browsing can be done with MacWeb 2.0, but required System 7.x as a minimum.

The PC will bridge the serial link carrying TCP/IP traffic onto the network using SLiRP.

Some resources I will be using include "How I introduced a 27-year-old computer to the web" and "Internet Access with System 6"