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.

All was 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! 

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 plastic case is very flimsy and 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 (apparently there are a few more robust injection moulded cases out there, but I have never come across one).

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 ventilation slots). 

The Z80 CPU, modulator and many of the main board electrical components are still available, but the ZX80 is quite delicate and very sensitive to
de-soldering and repair.

Loose Cassette Connector Sockets
Another very common problem with all Sinclair models using  cassette leads are loose clamps inside the connector sockets.
This causes the leads to slip out of the socket, or move around affecting program loading or saving performance.
I usually have spare sockets in the Sinclair Sales pages of this Sinclair section of the website, but if your soldering skills aren't up to removing the old and fitting the new then a gentle push with a small flat blade screwdriver is often successful in re-tensioning the spring contact.

Keyboard Problems

For non-working keys, keyboard membranes are still available from Rich Mellor at at SellMyRetro.