Tandy TRS-80 Model 100

History

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.

Restoration

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.





Electrolytic Capacitor Replacement Table for full Recap

Qty	Location(s)	Value	Voltage
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
1	C78	3.3µF	50V

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
RAM: 32KB
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

Links

Club 100: A Model 100 User Group



Last Updated: January 3, 2020