Been working this for about a week now. Little background on it. The plane left for depot two months ago with no hf problems, nothing in the previous 4 months as well. It landed at depot with #2 hf coupler fault and no tune tone. Depot serviced the coupler and were able to clear the fault and get the tune tone back, but they weren't able to transmit, blamed it on atmospherics :confused:, and wrote it up for an in-flight check. It landed back here with the no transmit problem.
It tunes just fine, breaks squelch, no faults in any freq range, receive is crystal clear, just no transmit and no sidetone. We've swapped or replaced r/t's, r/t mounts, couplers, interlock relays, #2 rf interlock relay, secure interlock relays, secure processors, secure rcu's, and control panels. This is a non scns a/c. We've checked the capacitor in the junction box, the dummy load at the coupler, the lightning arrestor, and numerous mic and tx aud lines between the interphone junction box, rt, and coupler.
When listening in from another a/c, you can hear it break squelch, then there's a loud high pictched hum/feedback like noise, but very very faintly (like hearing test faint), you can hear the operator asking for an hf check.
I'm at a loss for where to go with this. It's one of the stranger hf problems I've encountered. Any help would be much appreciated.
-Bods