This means I need to replace the membrane. ALl keys work this way including the offending numbers. First I need to confirm that all keys work from the motherboard side using a piece of wire to connect pins from KB1 to pins on KB2 using a lookup I found on Google to test the 6,7,8,9 and 0 keys.
#Sinclair zx spectrum motherboard mod#
With the composite mod complete I move on to the keyboard. In March 1983, Sinclair issued an 'URGENT' recall warning for all owners of models bought after 1st January 1983. Another issue was with the Spectrums power supply. This can be done with a simple piece of wire but supposedly a better picture can be achieved by soldering a 100uf capacitor between them (positive side to the PCB), so this is what I’ve always done: The original ZX Spectrum model experienced numerous changes to its motherboard design mainly to improve manufacturing efficiencies, but also to correct bugs from previous boards. The next step is to connect the top most hole on the where I disconnected the wire, to the output connector inside the modulator. Issue 4A and 4B Schematics, Issue 4A Layout. Once all these are disconnected I cover with heat shrink-wrap so it can easily be restored at a later date. Issue 1 Schematics and Layout (pdf) Issue 2 Schematics and Layout.
Next desolder the two wires from the PCB connected to the RF modulator on the left side (also circled above). First I disconnect the resistor from the output connector shown circled in the picture above. The composite mod is very easy to perform and only requires basic soldering skills. ZX Spectrum was my second comp (after ZX81) and even games were a selling point, it was an excellent tool for learning programming (and I dont mean BASIC).