Eric Bylenga
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Tandy TRS-80 Model 100

History TRS 80 Model 100 and accessories.

Actually made by Kyocera, this was the last computer for which Bill Gates wrote code. For myself a Tandy 102 was the first computer I ever personally owned (and the first computer on which I learned BASIC). Unfortunately that one broke a long time ago and I got rid of it.

I found this Tandy 100 at a previous job in a pile destined for the garbage. It came with a printer, tape deck, 3.5" floppy drive and of course the 100 itself.


I recently performed a full electrolytic capacitor and memory battery replacement in addition to a deep clean and general repairs. As you can see below, the memory battery was leaking and no longer holding a charge, there was corrosion around the electrolytic and one of the tantalum capacitors as well as corrosion and general poor condition of the battery terminals.

For a new battery I had a difficult time finding an appropriate 3.6V 50mAh NiCad battery. Somewhere on the internet it was recommended to try a super-capacitor instead to keep the memory intact. I settled on a 1F 5V super-Capacitor which fit in the space left be the battery. Jury is still out on how long it keeps the memory contents. I'll have to test it over a period of a few days.

As you can see, it works great again and feels fresh after a good cleaning! It's a real treat to know that it'll be functional again for years to come.

Gross Battery
Bad Electrolytics
Bent Battery Terminal

Electrolytic Capacitor Replacement Table for full Recap

Full Recapped Motherboard.
1 C83 470µF 10V
1 C92 0.47µF 50V
1 C86 100µF 6.3V
1 C84 470µF 6.3V
1 C90 1µF 50V
1 C85 33µF 10V
1 C82 4.7µF 25V
1 C52 1µF (Bi-Polar) 50V
4 C49,C50,C54,C55 10µF 16V
1 C103 220µF 10V
3 C75,C76,C77 47µF (Bi-Polar) 16V

I don't know if this is common but C40 also was leaking stuff. It's a dipped Tantalum capacitor labeled 473 J50 NIS C which equals a 0.047µF 50V capacitor.

As an aside I really love the positively wonderful amount of through hole electronics there is on a Model 100. There is a great deal of satisfying analogue components that make up the circuitry of this machine. The traces on the board look hand drawn too. The lines look like someone took the time to draft them up. Check out the full recap in the image below. (I apologize for the darkened edges of the board and the bright flash in the centre!)

Current Specs

Processor: 3 MHz Intel 80c85
Video: 240 x 64 (Full-Dot matrix) on a 240x8 monochrome LCD
I/O: Centronics, Tape, Bar Code, RS-232 (serial), Modem (300 Baud), System Bus
Power: 4 AA Batteries (or a 6V AC adapter)
Applications: Terminal, MS BASIC, Address Book, Text Editor
Back Ports
Model 100


Club 100: A Model 100 User Group

Last Updated: January 3, 2020