so this has been bugging me for like three weeks and i finally tracked it down last night so figured id share in case anyone else runs into this

basically my 7300 was putting out audio that sounded totally distorted on SSB, people kept telling me i sounded like i was underwater or like there was clipping everywhere even at low mic gain settings. i went through the usual stuff, checked the mic gain, the compressor was off, tried a different mic, same thing. RF power output looked fine on the meter and ALC was barely moving so it wasnt an obvious overdrive situation

spent way too long suspecting the finals because there was a faint smell one time when i keyed up but i think that was actually just something on my desk near the fan exhaust. anyway after pulling my hair out i finally hooked up a dummy load and fed the output into my SDR to actually look at the transmitted signal and the modulation was just completely asymmetrical, one sideband was way down

turned out to be a bad solder joint on the mic connector inside the radio. the board had a cold joint at the tip contact pin that was intermittently dropping out part of the audio path. resoldered it and the thing is back to sounding clean. such a dumb simple fix after three weeks of overthinking it

moral of the story i guess is always check the obvious mechanical stuff before assuming the DSP or finals are cooked

yeah cold joints on those mic board connectors are actually more common than youd think on the 7300, ive seen a couple come through with similar symptoms. the reflow process icom uses on that particular board seems to leave a few marginal joints especially around the connector footprints. good catch using the SDR to actually look at the RF envelope, most people just go off what other stations report and that makes it really hard to diagnose because everyones rx chain colors the audio differently anyway

one thing worth doing while you had it open is just hit all the connectors on that main board with a little pressure and see if anything flexes. theres a ribbon cable near the PA section that can also cause weird audio artifacts if its not fully seated, different symptom but same general category of problem. glad you got it sorted without having to send it in

this is exactly why i started just doing a full visual inspection under magnification before touching anything else on a radio that comes in acting weird. i had an FT-991 last year that was doing something vaguely similar, turned out to be a cracked via on the audio processing board, completely invisible without magnification. drove me crazy for days before i just started going over it inch by inch with a loupe

the SDR monitoring idea is a good one btw, gonna start doing that more systematically instead of relying on signal reports