Introduction: Create Macintosh Plus ROMs

This Instructable will guide you through the process of "ripping" EPROM images from from your Macintosh Plus ROM chips and (or) "burning" the images to new chips. The process will basically be performed twice to create both "hi" and "lo" ROM chips for your Mac Plus.

This documentation has the following applications:

  • Create replacement ROM chips / rare ROM chips
  • Back up existing or unique ROM chips
  • Sell ROM chips online

I created this Instructable after identifying bad ROMs as the root cause of a very strange error on my Macintosh Plus.

This guide is also applicable to Macintosh 128K and Macintosh 512(k,e).


You must have the following supplies on hand in order to proceed:

  1. TL866 or TL866II, or TL866II+ (Amazon)
  2. Access to a Windows PC (Linux & MacOS supported but not shown in this guide)
  3. At least 2x 27C512 28DIP chips (eBay) (Aliexpress)
  4. Macintosh ROM chips (Optional)
  5. Macintosh ROM Image files (Semi-optional)

Step 1: RIP ROM WHA?

Let's talk about "ripping" ROM images from physical chips. For simplicity sake I will describe the process of ripping ROM images on Windows, as it is the most straight forward process with the TL866II+. However, it is possible on Linux and Mac OS with more effort.

It should be noted that this guide will not cover how to physically uninstall or install your ROM chips but please understand removal and installation of ROM chips should be a delicate process. If the metal pins are damage your ROM chip may become an interesting piece of trash.

What is a "ROM" chip?

On the technical side, ROM is "Read Only Memory" — two physical computer chips installed on your Macintosh Plus logic board which issue commands to the CPU. The memory in the ROM chips is programmed to issue important instructions like loading the operating system from the hard drive and much, much more.

What does it mean to "rip" a ROM image?

Ripping ROM is the process of reading all of the ROM chip memory to your computer. You will need an image of an existing working ROM in order to produce new replacement chips. If you don't have working ROM chips or would prefer to download a copy, you can find many popular ROMs listed on the "Macintosh Repository" website — a great resource for the community (Direct Download link). I also host ROMs which I pulled from my own chips in GitHub, which you can find linked in the next section.

When the term "image" is used you can metaphorically imagine a "snapshot" of the entire ROM chip memory. You can consider the process like a photocopy. When we create the copy of the ROM chip memory using the TL866II+ programmer it is called "ripping".

How do I rip a ROM image?

Begin by downloading the appropriate Windows software for your TL866II+. If you purchased the TL866II+ manufactured by the company available from Amazon and linked to in the supplies section then you can download the software you need from here on the Autoelectric website.

Step 2: It's Ripping Time!

Once you have the software you need for your TL866II+ (or TL866 / TL866II) and you have confirmed your programmer is detected then you can proceed with reading or "ripping" ROM images from both of your ROM chips, which is covered in this step.

Screenshots in this section will illustrate the software for the TL866II+ but it is very comparable for other models.

Ensure your device is detected

For whatever reason your system may not play nice with drivers and software. When you open the programmer software in Windows ensure you see the message "1 Programmer Connected".

Select Your Chip

The TL866II+ totes support for over 15000 chips! Amazing! But... not important right now; we only need to support one type of chip; the "AM27C512 @DIP28". Don't confused the "AM27C512 @DIP28" for the "AM27512" — one has a "C" and one does not.

  1. Disable the options "Pin Detect" and "Check ID" from the lower left corner
  2. Click the "READ" button near the top or select "Device" -> "Read" from the menu bar.
  3. Click "READ" on the subsequent pop-up.
  4. Use the ~5 seconds the programmer takes to read your ROM chip to reflect on how neat this is.
  5. Voila! You have a ROM image... right? Maybe?

Verifying the ROM image

To start, you should not see a page full of "FF" — if you did then you either inserted your chip incorrectly or your ROM chip is dead. It's also possible that you selected the wrong chip, in which case you should reflect on your error before correcting it. I have attached a screenshot of a valid ROM chip; yours may vary depending on the rom version or image you're using.

If you know the version of ROM you have (there are A, B, and C where "C" is the newest for the Mac Plus) then you can simply compare the image to a ROM downloaded from the Macintosh Repository. I have also provided my own ROM images, separated into "hi" and "lo", which are available on my GitHub.

Save your ROM image

Simply click the save button or select "File" -> "SAVE" from the menu and save the output to a memorable location on your computer; you will need this file to burn to a new chip.

Repeat the process described in this step for both of your ROM chips.

Step 3: Burning ROMs

Burning a ROM simply means "writing" the ROM image we ripped from your chips or downloaded to fresh chips. If you didn't rip a ROM image from your chip you can find the images on my Github as well as on the Macintosh Repository here.

Programmer Software Changes

  1. Click "Select IC" at the top or click "Select IC" -> "Search & Select" in the menu and then change the chip to "AM27C512 @DIP28".
  2. If you don't have the ROM image in your programmer from the previous steps, simply click the "OPEN" button at the top or "File" -> "Open" in the menu and select the first of the two images you saved in the previous step or the appropriate ROM files downloaded from Macintosh Repository.
    • If you are using the ROM files from Macintosh Repository there are additional steps which will not be covered in the immediate release of this Instructable.
  3. Click "PROG" at the top or "Device" -> "Program" from the menu and "Program" on the following screen.
  4. Repeat this process for both the "hi" and "lo" ROM chips.

That was it! You can load or "rip" the ROM image from the new chip and verify it against the ROM image you loaded into your programmer or simply re-install it back into your Macintosh Plus and perform a test boot.

With this new process you can help our friends or even sell ROM chips!

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