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MZ-80K 4 MHZ Upgrade 
written by  
kindly supported by Bernd Krueger-Knauber  

There are several ways to upgrade the MZ-80K to 4 MHz. I put the one found in my own MZ-80K here first. All others which I found in the SUC Magazines are shown on the next pages.

Some changes of the recorder are necessary if you also want to read/write tapes while using the 4 MHz CPU speed. Solutions for this are also shown on the next pages done by SUC members in 1983. My MZ-80K is deeply modified but not the recorder. This means that I can read/write tapes using 2 MHz and while using 4 MHz it reads/writes tapes only with double speed (2400 baud).

I got my MZ-80K by an ebay auction and its previous user did all the modifications which I'll explain now. Take a look of the mods now:

The 4 MHz upgrade is shown green bordered. The other two new PCBs enable my MZ-80K to display 80 characters for CP/M. This modification will be described asap in a new article.

The 4 MHz upgrade on a grid board ( soldering side view ).

The female connector at the upper left side connects the speed indicator LED and the 2/4 MHz switch to the board (shown with male connector not connected).


Component side view.

Two srews keep the board on distance to the motherboard and are glued on it.

Diagram and new PCB
( kindly made by Bernd Krueger Knauber )

The new PCB (Printed Circuit Board)

The IC pins shown in blue are to connect to the pins on the board (e.g. IC-47-17 = IC47 pin 17 on the motherboard to the PCB pin JP3).


IC 35

+5V and ground

All wires are soldered directly to the IC-pins.

This article is unfinished and will be continued. A modification for 80-characters will be shown next too. In the meantime check the pictures, schematic diagrams and PCBs for this:

Download 80-character mod (for CP/M-80k support) with all original schematic diagrams from an unknown fan (ZIP 1.098kb)

Download ROM-switch (necessary for the 80-character mod (for CP/M-80k support) ZIP 371kb

Download all files for the 4 MHz upgrade (ZIP 181kb)

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last updated January 10, 2010

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