YouTube user Spawn Wave released a teardown video in which he detailed what appears to be a fundamental design difference between the left and right Joy-Con controllers. While the right has a full, separate antennae, which should lead to stronger connectivity strength, the left’s antennae is build into the circuit board. A metal box positioned next to the antennae could also be interfering with signal strength, so Spawn Wave decided to run a small wire in the opposite direction to extend the antennae with less interference, attaching it to a small bit of solder located halfway down the controller. It’s then sandwiched underneath a piece of plastic, followed by the battery.
Once the antennae is installed, the left controller not only seems to not suffer from the same synchronization problems as before, but it even works more reliably than the right. At about about 20 feet away, the controller even works without issue when Spawn Wave puts it behind his back — an action that renders the right Joy-Con essentially unusable. At 30 feet, the right Joy-Con is completely unusable when placed behind his back, while the left Joy-Con functions without issue. It even functions perfectly when he exits the room and hides behind a wall.
While we can’t really recommend that you crack open your Joy-Con and attempt surgery yourself, the effect on connectivity is undeniable. Nintendo may very well have to issue a recall or give away redesigned Joy-Con controllers in the future if it wants to solve this problem. For now, just cross your fingers that you can find a Pro controller.