Definitely check the alignment. I have seen very deaf receivers caused by miss alignment.? If that doesn't do it, it should be very straight forward to trace the signal. You don't really need much in the way of test equipment. You might start with a probe on the input of the audio amp.
Ashhar has kindly put in many test points that you can test from.? More or less follow the yellow brick road back to the antenna.
This drawing outlines both the transmit and receive signal paths
73
Dave
_Dave_ AD0B