ZX81 Composite Video with Backporch
The ZX81 Composite video PCB replaces the RF modulator in the ZX81 which will give you a clearer and more stable picture on modern TV’s
This design is based off the schematics from zigg.net which have been around for many years and is tried and tested.
Installation: (See pictures for more details)
- Remove the lid from RF Module
- Desolder (or cut) the resistor connected to the RF output pin.
- Cut the 5V wire from the motherboard to the RF Module
- Cut the input wire from the motherboard to the RF Module
- Solder cable from GND pin on the PCB to the GND track on the ZX81
- Solder cable from 5V pin on the PCB to the 5V wire on the ZX81 (On the motherboard, not on the RF Module)
- Solder cable from the IN pin on the PCB to the input wire on the ZX81 (On the motherboard, not on the RF Module)
- Solder cable from the OUT pin on the PCB to the RF output pin on the RF Module.
Note: This backporch mod is not required for ZX81’s with a newer ULA or ULA replacement like the VLA81 that already produces a backporch signal.