Testing angle sensors on Z80

So I've got an issue with a Genie Z80/60 (s/n starts with Z8015). I'm suspecting the primary boom angle sensor is shot as it reads 40 degrees on the LCD panel regardless of boom position. Just wondering how one would go about testing the sensor to make sure its not a wiring issue. The angle sensor appears to be located at the rear of the boom and is a small, sealed black box with an adjustment link attached to it.

Testing angle sensors on Z80