TRS80 Model 4 Internal FreHD Install

A few pictures showing the installation of a FreHD Hard Disk Emulator in one of my TRS-80 Model 4's.

The mounting chassis is the frame from a dead Seagate ST4766N hard drive.  I picked up a box of these in the early 2000's and that sat in the corner of the workshop waiting for a project just like this.  The FreHD is mounted on a piece of plastic attached in the drive frame.

The FreHD is connected to the Model 4 expansion connector with a long 50 way ribbon cable.  Installation required removal of the Model 4 PCB so the ribbon cable could be routed between the PCB and the metal chassis frame.  The cable comes out at the top of the Model 4 chassis and then attaches to the connector on the FreHD.

An SD Card extender (available on eBay) was used to make the SD Card accessible outside the Model 4 case for the few times I want to change the installed software.  I don't change the software on the cards often so having the SD card accessible from behind the machine rather than from the front isn't really a problem.  The SD Card extenders work well but the FreHD doesn't recognize that the card has been removed and inserted because it relies on a physical switch on the SD Card socket.  Best practice is to power down the machine before changing the SD Card if you use an extender.

FreHD installed in Model 4 Drive Bay. Expansion cable visible.

Alternate view showing SD Card extender cable

Not as shipped from the factory but a tidy installation



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