The test card on the Hedghog is generated in a different way to the one on the Aurora.
In the Aurora the test card is stored in memory external to the FPGA as an image and can be changed at any time to any image.
In the Hedghog it is generated within the FPGA by an algorithm and cannot be changed.
The Hedghog test card is harsher. Much of the test card is the same on both odd and even fields which gives rise to a degree of 25 Hz flicker.
The test card and grey scale are freebies as they use the logic that was left over in the FPGA after building the converter and no extra memory is required
.
Jac has done a good job of explaining the audio carrier level. Setting the pot at half way is a good starting point.
It is easy to damage the surface mounted components removing the FPGA board.
Removing the board shouldn't be attempted until the Hedghog PCB is removed from the case as a lot of strain can be put on the components close to the mounting holes if left in the case.
Frank