LooseCannon,
I was thinking the same thing, I had never seen what Buckskin described, until today; yeah usually the radio will still key up, at least if the driver/final stage are good. (& the light is switching)
I was running my Cobra 29 LTD Classic on the bench, listening to skip rolling and then I noticed one of my locals cutting in and out, so I went to key up and let him know that maybe he was having an issue over there!
As it turns out I was the one having an issue, I noticed when the s-meter was not moving anymore! The light was changing from green to red, but no transmit!! no receive, I was like wtf! (also, I still heard faint static when this happened, but no incoming signal)
Switched the radio off then on and the receiver came back (TX at the same time), after a little while the problem happened again, light was still switching green-to-red but the receiver was going dead and the radio wouldn't transmit, so maybe a mixing circuit? 
I haven't looked it over yet, and i'm not proficient enough to "call it out" without actually looking around the radio and measuring something; but apparently this can happen, weirded me out for sure!
notes: my radio was manufactured in 1994, it is ready for capacitor replacement as they are all original. I could have a shoddy coax that has an intermittent connection. :/
