Here's a couple of suggestions without spending any money:
Can you hear the carrier and PTT click on another receiver?
If "yes", then fault is possibly a bad connection on the mic input to SL40. Try checking and reseating the D-sub connector to the radio.
If "no" carrier then check connections to antenna. If there's nothing wrong then next step may be to the avionics shop...
Paul vS (yes I'm also a Van)
Building RV-6A #22320 O-320 FP. Wings and tail complete, working on fuselage
Flying my Aeroprakt A-22 STOL and the aero club's RV-9A while I build