Apple Macintosh Plus


Classic Mac Tech Info



Revision 820-0174-A (1985)

Revision 820-0174-D (1986/87)

RAM Modules


When Mac does not boot but shows static garbage on the screen, it is likely the CPU does not work correctly. One of the reasons may be a broken ROM chip. There were three versions of the ROM in Mac Plus, marked on the chips as A, B or C. Their images can be found for example on Macintosh Repository. The easiest way to diagnose it to compare the content of the ROM against the image. The ROM image is a combined 128K file, it needs to be split into 64K chips: HIGH (342-0341, bytes at even addresses) and LOW (342-0342, bytes at odd addresses). Programmer’s application usually gives a possibility to choose the split when loading image, however for example in TL886 MiniPro app, these options are incorrect and switched (high for low and vice versa).

The replacement chips should be compatible with 27C512, to avoid troubles dealing with EPROM erasing, EEPROMs are a good idea, for example Winbond W27C512-45Z.

Power and Analog Board

Capacitors list for recapping:


The battery is a quite rare or expensive 4.5V PX-21. The good news is that battery is not needed to boot the Mac Plus (unlike newer pizza-box Macs). Of course it is still required to keep the time and date with no power supply.

Floppy Disk Drive

Sony MDF-51W-10 is a double density 800K drive. It will not read high density disks formatted in later Macs at 1.2M.


Model number M0110A F




Another kind of protective shield:


The famous internal side of the case with signatures of the creators.

2 thoughts on “Apple Macintosh Plus

  1. This is a very great article. May you improve the capacitors list? Maybe with the compatible replacement components?


    1. Thank you. I could, but I don’t know how exactly. Could you elaborate more? For the replacement capacitors, generally you just put the same capacitance with voltage ratings equal or higher.


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