Though still not a real powerhouse, the 16 or 48K RAM and slightly better keyboard than the ZX80 and ZX81 made this a moderate leap forward for Sinclair. Well, you can Read the full story on the Register. And definitely look at the Flickr page of Rick Dickinson with all the images showing how the Spectrum was designed.
This computer was one I already owned before starting my collection. It was given to me years ago by my father in law, and was stored somewhere in a dark closet ever since. After bringing it back to the light, one of the first things to do was modifying it for composite video output. There's an extensive description on the retrogamescollector website that I followed. But instead of connecting straight to the video signal I used the same setup as used to modify my ZX81, with a transistor and a 100 ohm resistor.
|Transistor on the left. 100 ohm resistor from centre pin to the metal shield.|
Unfortunately the Spectrum suffers from the same problem as the ZX81: the plastic of the membrane keyboard has become brittle, and it almost immediately broke when I removed the cover.
|Crack.. Oh No.. Not again...|
|It's easy to remove the keyboard|
|DC- 2.1x5.5mm Socket|
Then the screen went blank, and a terrible smell came from the power supply. After opening the PSU housing I found I could barely touch the transformer since it was really hot. and the rectifier diodes did not look good either.
Spectrum repair Guide, which saved my day.
Here I learned that the transformer actually is protected by a thermal fuse. And even though this fuse is not replaceable it is possible to mount a 160mA fuse in parallel so the transformer will work again.
Next I incorrectly assumed the centre pin of the PSU was positive voltage and the outside was negative, so the Spectrum still did not work. But after correcting this it finally came back to life.