The headphone jack will be placed at the
upper left part
of the PCB. You can help
yourself by finding the little square.
Or, you can simply check the photo below:
Make sure that the round part of the headphone jack is facing up. That way, you'll
be able to connect your headphone jack to your headphones.
While placing it on the board, check if everything is well-adjusted before soldering.
Your Synthia should look like this by now:
