so this has been driving me nuts for about two weeks now. my 7300 is working perfectly on 40m and 20m, receive is clean, sensitivity seems normal, no complaints. but on 15m and 10m the receive just falls off a cliff. like i can still see signals on the waterfall sometimes, barely, but they're way down compared to what they should be and actual audio is almost nothing. noise floor looks weird too, kind of flat in a way that doesnt seem right.

TX still works fine on all bands, power output is normal, swr is fine, i checked it with an external meter. so it's definitely a receive path issue and it seems band-specific which is what's really confusing me. antenna is a fan dipole that's worked fine for years, and i swapped to a dummy load and a separate known-good receiver to rule that out — same result, the fan dipole is receiving fine on 15 and 10 with the other radio.

anyone had something like this with a 7300 or similar rig? im wondering if it's a bandpass filter issue or something in the preamp switching. i havent opened it up yet, kind of hesitant since it's still sort of under warranty i think, but i might be past that window honestly.

yeah that pattern really does point at the bandpass filters or the LPF/BPF switching relays. the 7300 uses a bank of filters and if one of the relay contacts is dirty or failing you'll get exactly what you're describing — TX path is separate enough that it can still work while receive tanks. the fact that it's specifically the higher bands and not a gradual rolloff across everything makes me think relay before i'd think a cap or something passive in the filter network itself.

before you crack it open i'd try the reset procedure if you havent already, not because i think that'll fix it but just to rule out some weird firmware thing, and also check if the built-in preamp toggling on and off changes anything on 15m. if turning pre1 on makes zero difference on a band where it normally helps, that's another clue the signal path on that band is broken somewhere upstream of the preamp switching.

honestly though if you're past warranty just open it up. the 7300 is pretty serviceable, icom's service manual is floating around online and the BPF unit is a separate module. might just need a squirt of contact cleaner on the relay if you can get to it.

had something vaguely similar on an older ic-746, turned out to be a cold solder joint on one of the filter board connectors. the vibration from moving the radio around had worked it loose over time i guess. wouldnt have found it without reflowing a few suspicious joints near the band switching area. just something to keep in mind when you do get in there, worth a look at the connectors before assuming the relay itself is toast.