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TRS-80 Model II Lives Again

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A lot of people had a Radio Shack TRS-80 Model I. This was a “home computer” built into a keyboard that required an external monitor or TV set. Radio Shack has since updated the computer to a Model III. It was a popular “all-in-one” option, with room for a monitor and even a floppy disk. However, the Model II was less popular. cause? It was for businesses and priced accordingly. [Adrian] got the Type II, which was in a terrible state, revivedYou can watch a video of how he did it below.

The Model II, much to Radio Shack’s surprise, resembled the old “Trash 80” that was heavily used by businesses. But it had more sophisticated features, including a 4MHz CPU. It was a breakneck speed for those days. It also had an 80×25 text display and his 500K his 8 inch floppy drive. Serial and printer ports were also standard equipment.

It had some interesting features. The floppy drive’s spindle ran on his AC power, and if the computer was on, the disk would spin. Additionally, it had bank switching to allow it to go beyond 64K and didn’t need to share running memory with the video display. Theoretically half of the memory was bank switchable so the machine he could go beyond 64K. In practice, early models didn’t physically have enough expansion space to handle more than 64K.

You need a floppy to boot the machine and in previous videos the computer didn’t boot properly. Given the years of poor storage, that’s not all that surprising. You can watch machines being dismantled, schematics being examined, and ICs being tested. But in the end, my computer seemed to fix itself. With this kind of experience, you can guess what happens next. Of course it fails again.

Theorize that the heat cured the area that was good on the test, [Adrian] I replaced the chip and it took me a while to confirm that the disk controller was bad. Finding the bad chip was relatively easy once the bad area was known.

If you have any memories of Model I, what do you think? build oneWe would love to see these old machines restored rather than utterly destroyed.? a little choice.


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