Original ZX Spectrum refurbished

The speaker was rusty, marked with "X" sign by somebody and dead:

According to the schematic of issue 2, the speaker is driven directly by the ULA output through two diodes to reduce the ULA output voltage, as I understand it:

Some sources said the speaker impedance should be 40 ohms, others 200 ohms. In any case, I couldn't find a replacement speaker other than 8 ohms. So I decided to use it in series with a 39 ohm resistor and add an S9013 transistor as an emitter follower, similar to the circuit of issue 3:

The new speaker and additional elements are a perfect fit:

The resulting volume level is completely good.

The keyboard wasn't working due to damage to the membrane near both ends of the connectors. I initially tried cutting away the damaged areas, but that didn't help due to the poor condition of the conductive tracks. So I bought some conductive silver-based paint and repaired them:

This helped, and now the keyboard worked, except for two keys, "B" and "N," as far as I remember. It turned out that the conductive track inside the membrane was damaged, and it seemed impossible to repair... But I tried it anyway:

It took me a few days because silver paint needs at least 24 hours to dry.

Finally I got it to work:

However, I then discovered a newly-produced membrane on a German website:

This is certainly much better than 40-years old, of course:

All that was left to do was clean the rubber keys with isopropyl alcohol: