so ive been chasing this for like three weeks now and im at my wits end. my 7300 will just randomly drop out mid transmission, like the power drops to zero for a second or two and then comes back. sometimes it happens every few minutes sometimes it'll go an hour without doing it. no pattern i can figure out with band or mode or anything like that.

first thing i checked was the power supply — im running an astron RS-35M and the voltage looks rock solid on my meter, no sag under load. tried a different coax, different antenna, same thing. ran it with the lid off for a bit thinking maybe thermal but it does it cold too so probably not that.

the weird thing is the display stays on the whole time, just the RF output drops, ALC meter goes to nothing during the glitch. i was thinking maybe something in the PA section or the ALC circuit itself going wonky. anybody dealt with this before? im halfway considering sending it to Icom but thats a whole thing and probably expensive.

had almost the exact same thing on mine last year. turned out to be a cold solder joint on one of the driver board connectors — the internal ribbon cable that connects the PA to the main board had a connector that wasn't fully seated and would flex just enough under thermal expansion to lose contact. worth pulling the covers and reseating all the internal connectors first before you go chasing something more serious. takes maybe 20 minutes and costs nothing.

also worth checking is whether you have any RF getting back into the rig somehow. i know you swapped coax but if your feedline runs near the power cable you can sometimes get common mode garbage causing weird ALC behavior. threw a few ferrite clamps on mine and it helped with a different issue i was having.

does it do it on all bands or just certain ones? my buddy had something similar and it was only on 10m, ended up being a bad filter cap in the LPF board. not saying thats your problem but worth narrowing down. also what firmware version are you on, theres been a couple weird bugs over the years with ALC behavior on older firmware that icom quietly fixed.