TRS-80 Model I Expansion Interface Delay Line IC Upgrade for final revision Tandy/Radio Shack TRS-80 Model i Expansion Interface units.
This is a project that I found online and had some boards made up and populated them with the components. I have been using one of these in my own personal TRS-80 Model I expansion interface for about 7 months now with no issues. The idea behind these is to replace the faulty digital delay unit IC on the expansion interface board with modern replacement components in order to keep the interface working correctly for many years to come. With the last of these expansion interface units made in 1981, the components in these aren\'t getting any younger and the original type component is no longer available. The issue my own interface unit had was it kept blowing up a particular RAM IC, and it was traced back to a faulty DDU IC....IC# Z37. The modern replacement is a DS-1100 delay line IC that is a surface mount chip and the board was made to allow that chip to work with the vintage hardware easily and with a clean install/look. Only the pins required to mount the new board in place of the original IC are provided. You can either solder the new board directly into the main board like the original IC or you can mount a socket to do so as well, but you will have to remove some pins from the socket before you can install that on the main board.
This mod/fix is for the final revision of the Expansion Interface board. A picture of the unmodified board is shown for reference, as well as a couple of pictures of the original IC removed from the board and a picture of where it\'s located on the board. If your board does not look like the boards in the photos, you do NOT have a final revision board and you will not be able to use this mod. As a matter of fact, the earlier boards do not even use a digital delay unit, so this part will not work for you if you have the earlier board. Please refer to the pictures to make sure you have the correct version of the board in order to use this mod.
Please note that this mod requires some soldering/de-soldering skills for installation. If you are not comfortable with soldering or de-soldering, you may want to seek out a professional to help you install the mod.