Sinclair ZX80


Having resigned from Sinclair Radionics in 1979, Clive Sinclair concentrated on a new computer project at his Science of Cambridge company.

Working closely with Jim Westwood, who had previous experience of computer design and construction, building, Sinclair wanted to build a computer which was within the reach of the man on the street. Although an amazing product at the time, everything was designed around saving costs.

It was built with just the base necessities, using off the shelf components with no custom built proprietary chips at all.

Based around the Z80 processor, the CPU had to handle all of the computer functions. There was no video chip so when the CPU was working on something else, the screen went blank until it had finished - this caused the famous and very annoying ZX80 flicker.

Another issue was that the main RAM was used to store the screen display, with the result that the available screen size would gradually decrease as the size of a program increased - with 1KB RAM, running a 990 byte program would result in only one row of characters being visible on the screen!

There was no colour or sound support, limited (1K) memory and a built in BASIC which only supported whole numbers.

The single key-press generation of entire BASIC keywords was advertised as being to designed to increase entry speed and reduce syntax errors, but in reality was implemented to save on memory with only 1K of RAM fitted.

The issue 1 machines were housed in a cheap, slim, vacuum formed white plastic case, held together with small plastic studs and was powered by a power supply which wasn't always white to match the case!
Issue 2 machines had a rigid ABS case which was a huge improvement.

Costing just £99.99 (£79.99 in kit form) it met its price point and in 1980 the ZX80 was launched, named after its processor and year of introduction. It sold over 100,000 units in its life time, introducing many people to the computer world who could not afford the more expensive (and more capable) systems out there at the time. Its launch set the scene for the whole budget UK home computer market.

Technical Details:

  • CPU Model: Z80A
  • Speed: 3.25MHz
  • RAM: 1KB
  • Membrane Keyboard
  • Optional 1K, 2K or 3K RAM packs (later a 16K version)
  • Single-key word entry
  • Local price at launch: £79.99 (kit-form) - £99.99 ready-built)

Problems and Issues
I haven't had too many ZX80's through the workshop as they are quite hard to get hold of now, but my main observations:

The vacuum formed plastic cases used on the issue one ZX80's made by Tek were is very flimsy and are likely to be damaged nowadays unless you can find a nice, well cared for boxed example.

Obviously, not really repairable if you have a bad one, but the issue two machines which were made by Timex were made using the same ABS type cases used for the ZX81's which are much more robust.

Missing, or broken plastic rivets which hold the top and bottom of the case is also a problem. New ones are available from Rich at RWAP software on the "SellMyRetro" website.

There were problems with durability, reliability and in particular, over-heating. Despite appearances, the black stripes visible on the top rear of the case are merely cosmetic, and are not actually ventilation slots!

The Z80 CPU, modulator, RAM and many of the main board electrical components are still available, so electronics wise repairs are quite easy.

The ZX80 is quite delicate though, and very sensitive to de-soldering and repair, so be careful with the heat.

From a physical point of view, keyboard membranes often fail, but spares are again available from Rich at SellMyRetro.

The cassette lead points are also often damaged, or worn, so connection with the jack plugs is poor.  These are available in the shop and are the same type as the ZX81 and Spectrum.


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