so this has been driving me nuts for about two weeks now. my 7300 receives perfectly, everything looks normal on the waterfall, audio is good, all the menus respond fine. but the moment i try to transmit anything — even just keying up with no mic audio — the rig just... dies. like the display goes dark, the fan spins down, and then after about 3-4 seconds it reboots itself and comes back like nothing happened.

i swapped out my power supply first because that seemed obvious, tried it on a different 30A supply i borrowed from a buddy and same exact behavior. so i dont think its a PSU sag issue. SWR on the antenna is fine, ive checked it with an external meter, like 1.3:1 on 40m which is where i do most of my operating.

before i ship it off to icom or find someone local to look at it, does anyone have a clue what subsystem this would even point to? the finals? some protection circuit thats tripping? i havent opened it up yet because honestly im a little nervous about voiding whatever warranty is left on it, but i bought it used so probably no warranty anyway. any ideas would be really appreciated, been off the air for two weeks and its killing me.

that reboot behavior when you key up is almost certainly a protection circuit triggering, not an actual component failure — at least not yet. the 7300 has overcurrent protection that can cause exactly that symptom if the PA stage is drawing too much on TX. could be a bias problem with the finals, or one of the driver transistors is getting weak and causing the PA to work harder than it should to make power.

before you do anything else, try transmitting into a dummy load if you have one, and dial the power way down to like 5 watts. if it still reboots at 5W into a dummy load then yeah youre probably looking at something in the PA chain. if it holds at low power but fails when you crank it up that narrows it down a bit differently. also worth checking if it does this on all bands or just certain ones, because a finals issue sometimes shows up worse on certain frequency ranges depending on which transistors are stressed.

i fixed a similar issue on an older 746 years ago, turned out to be a cold solder joint on one of the driver board connections that only opened up under the thermal load of transmitting. not saying thats your problem but its worth having someone probe around with a scope before just swapping the finals blindly.

had almost the exact same thing happen to mine last spring, though mine would also throw an error code before the reboot which yours apparently isnt doing. ended up being a failed electrolytic cap on the PA board — one of the filter caps had gone high-ESR and wasnt holding voltage steady when the PA started pulling current. tech found it pretty quick once he got in there with an ESR meter.

if youre not comfortable opening it yourself honestly just find a local tech, a lot of the icom authorized repair places arent that backed up and it probably wont cost a fortune to diagnose. just the diagnosis at least tells you if its worth fixing or if its gonna be cheaper to find another used one.