Sinclair ZX Spectrum Service Manual 
Spectrum For Everyone  https://spectrumforeveryone.com/ 
29 
5.5 KEYBOARD STRUCTURE 
The keyboard is connected horizontally in eight blocks of five keys and vertically in five blocks of eight 
keys. The diagram below shows the configuration. It follows that is any block of five keys fail the fault is 
with KB2 circuitry or the 8-way membrane, and that if any block of eight keys fail the fault is with KB1 
circuitry or the 5-way membrane.