Description
The computer is originally made by Kyocera, Japan and called Kyocera 85. Later the rights was sold to Tandy Corporation which sold it through their Radio Shack stores. It became very popular and sold more than 6 million units.
The platform was also used in the Olivetti M-10 which has a nice flipping display and the NEC PC-8201 and PC-8300 which have a different keyboard layout.
The computer was very popular among journalist and other people that needed to write text on the go. The small form factor also made it popular in science laboratories as a programming terminal for controlling measuring equipment through RS-232. It can be powered around 20 hours by normal AA batteries that can easily be swapped.
It contains a version of Microsoft BASIC 80 in ROM where part of the code was written by Bill Gates himself. Other programs include a terminal program, an address and phone book, a to-do-list and a text editor.
The model 100 was followed by a model 102 that was almost identical but 1/2 inch thinner and one pound lighter. This could be done by changing from through hole components to surface mounted devices. Later it was succeeded by the Tandy 200 that had a much bigger display that could be flipped up as a regular laptop.
Relevance
It is one of the first computers in the notebook style form factor that included a large display, full-size keyboard and build in replaceable batteries. All that in a the same size as a block of A4 printing paper.
Compared to computers of similar form factor like Epson HX-20(LINK), Amstrad NC100(LINK) and Cambridge Z88(LINK) it had the largest physical screen with a high resolution and the best keyboard. That made it great for writing text.
Gallery
Front 
BCR connector 
RS-232, printer, cassette 
Power, LCD contrast 
Bottom 
Opened doors 
Internal view 
Mainboard 
LCD and keyboard 
Main menu after power up 
Microsoft Basic
Specifications
| Manufacturer | Tandy Coporation |
| Model | TRS-80 Model 100 |
| Form factor | Portable notebook computer |
| Released | 1983 |
| Price | US$ 1399 |
| CPU | 2.4 MHz Intel 80C85 |
| RAM | 24 kB |
| Storage | 32 kB ROM |
| Display | 7.9″ LCD 240×64 pixels, 40 characters x 8 lines |
| OS | Custom |
| Dimensions | 300 x 215 x 50 mm |
| Weight | 1,400 g |
| I/O ports | RS-232, parallel, BCR (barcode reader), cassette, System bus interface DIP socket |
| Power | DC 6 V plug, 4x AA batteries |
| Special features | One of the first notebook style computers with keyboard, LCD that runs on batteries. The Caps Lock button is a latching switch like on a typewriter. A huge high resolution display for the time. |
| Condition | Like new condition with a few scratches. Working |
| Accessories | – |
| Serial ID | 312100032 |
| To do | Add 2×8 kB RAM |
Purchase
This computer is not very common in Denmark. The sibling Olivetti M-10 once showed up on DBA but I did not got it because I didn’t find it very interesting at the time. This computer was bought on eBay as untested or not working. The auction was won at the last moment and shipped from England.
Restoration and modification
Since the computer was bought as not working I knew that something had to be done to make it work again. The auction did not describe any problems in details so I just had to wait to receive it.
When I first powered up the computer nothing happened. This can be a good sign caused by a blown fuse or bad DC plug connection. However after a little testing I saw that the contrast potentiometer did something. The display could be changed from completely blank to all black. I searched around to see if anyone had a similar problem and maybe a solution. I did not find much useful information. I checked the voltage supply to most of the chips and that seemed fine. My problem with comparing my computer with others was that the mainboard looked different in mine. Most others had the three DIP40 ICs mounted in a straight line. That made it hard for me to compare what they did to what I had to look out for.
After a while a stumbled upon a video about repairing a Tandy 100. Jeff does a nice in depth walkthrough of his troubleshooting and uses a logic analyzer to investigate communication with the RAM. In the end he managed to get it back to life by changing a faulty RAM chip. Up to 4x 8 kB can be installed. I thought it was a long shot but tried to do the same operation on mine. The only problem is that three out of four RAM circuits is mounted in a socket, but the one I had to change was the one that was soldered. I desoldered it and mounted a DIP socket instead. After inserting a RAM chip from one of the other sockets I flipped the computer around and saw that it came to life. I was very thrilled that I got it to work again. I would never had thought about doing such a deep analyze of the problem myself.
It still has some power problems, since it doesn’t power up every time I turn it on.
A simple upgrade that I would like to do is to buy two more 8 kB RAM circuits to expand it to the full 32 kB.
The form factor of this computer has been popular among hackers where some have swapped the mainboard for a Raspberry Pi and a better display. Recently computers in the same form factor has been developed like READY! Model 100 and DevTerm by clockwork both powered by Raspberry Pi.
I’m actually working on a project myself because I wanted to build a potable Raspberry Pi computer. I just didn’t liked the idea about reusing a vintage computer for it. Instead I’m going to laser cut an acrylic cabinet in the same dimensions. The design will be a mix-up between the Tandy 100 and IBM Thinkpad design elements. Based on a Raspberry Pi 4, USB power bank, a 1920×480 HDMI display and a Thinkpad keyboard.
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