Flex 6600 transmits for a few seconds and then stops

My Flex 6600, with Smart SDR 3.7.4, will only transmit for a few seconds and then stop. This happens no matter what mode I'm in--SSB, FT8, or "tune"

If I hit tune, for example, with "Tune PWR" up about 20%, I'll see about 5 watts of output for a about 5 seconds, then it will jump up to about 20 watts for just about 1 second, and then it will stop transmitting. The TUNE button remains blue. as if pressed. If I press the TUNE button again to turn it grey, I'll get the "Interlock is previnting transmission" error (yes, I'm in band).

I'll see the same behavior in other modes. In SSB, if I give a steady "ahhhhh" into the Mic, with RF power turned up, I'll see a few watts for several seconds, then the power will kick up to 80 watts or so, and then less than a second later, all the power will cut out. (I tested connected to a dummy load/wattmeter.)

The power button on the transmitter will switch back from red to green after the power cuts out and it stops transmitting.


Is my radio fried?