ZX Spectrum Composite Video Mod

This is the bypass modification, which enables the UHF modulator to produce a composite video signal to feed to the "video input" socket of a modern television. It involves disconnecting the UHF signal from the modulator socket and connecting the composite video signal instead.

First, de-solder one end of the resistor that connects to the centre pin of the aerial socket.

Then de-solder the two external wires coming out of the UM1233 UHF modulator. These wires provide the video signal and +5 V power to the UHF modulator. Notice that the composite video signal wire passes through the hole with the plastic sleeve.

Use a small length of wire and pass it through the spare hole with the plastic sleeve. Solder one end to the video signal pad, and solder the other end directly to the centre pin of the aerial socket.

Connecting a wire directly like this should be fine, but if you have any spare electrolytic capacitors, then you could add that in series to the wire. The capacitor simply provides a DC block and decoupling.

Here is a view showing the resistor terminal connecting to the centre pin of the aerial socket. This terminal requires de-soldering and the resistor pushed out of the way. Avoid moving any of the other components.

Here is the reverse side showing the PCB tracks. The animation above shows the solder points where you should de-solder the external wires to the UHF modulator.

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