Thanks Rishi & Italia-Linea. The spoke idea was ingenious, and tried it, but the cycle spokes are too thin for this purpose. I had an allen key set, so tried one hole with them. 3 mm allen key fits best - so went out & bought 3 more allen keys of 3 mm. Put them all in & nothing happened. I tried to pull out the HU then with the keys still in place. It took some effort, but finally the damn thing did come out. Found the antenna wire dangling behind as suspected. Fixed it, and voila - the radio is working once again. Thanks everyone for the suggestions.