Modifying a +2A or +3 to Output Composite on the RGB Port

Although RGB output offers the best native quality available from a Spectrum machine, for nostalgic reasons or for ease of connectivity, Composite output is generally the easier type to work with.

The 48K model can be modified using the simple composite mod, and the 128 and grey +2 have composite output on pin 1 of the RGB port, however the +2A and +3 models no longer carry this output.

If you want to reinstate composite output on pin 1 as on the 128 and grey +2, follow these steps:

Step 1: Construct the circuit

Tools needed:

  • Soldering iron
  • Stripboard or perfboard
  • 3 x 1N4148 diodes
  • 1 x 2N3094 NPN transistor
  • 1 x 2K2 resistor
  • 1 x 75 ohm resistor
  • Some insulated wire

Construct the circuit on perfboard according to the following schematic:

Click for full size version

Step 2: Install the Circuit

Composite circuit in place on a Spectrum +3. Click for larger version.

Remove R44 from the PCB, and install a connection from the north pad of the R44 to the TO_R44_IN connection on your circuit. Attach the other points as shown on the schematic, and anchor the circuit to the PCB using double sided tape.

You can now use a simple DIN to phono adapter on your +2A or +3 that will also work on a 128 or Grey +2.

Do note that after performing this modification, you will be unable to use an RGB cable without an external power source for the switching signal.

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