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.

LINKS

• Wikipedia
• TRS 80 Model 100 Repair Part 1
• EEVblog #116​ – Retro Teardown – Tandy Radio Shack TRS-80 Model 100
• The Model 100 Users Group
• Daves Old Computers – TRS-80/Tandy 100/102/200, NEC 8201/8300
• Ira Goldklang’s TRS-80 Revived Site