At one level I know what I did, I let the magic smoke out of the motor
driver. I had a 9 volt transistor battery to power the electronics
(measured voltage 8.4) and a 9.6 volt RC battery for the motors
(measured voltage 11.3). Turned on power switches; saw/smelt smoke;
disconnected everything. Visual inspection of L293D looks bad; no
longer flat on top. Measured resistance across motor power leads is 5
ohms. Rewired power to use transistor battery for both electronics
and power. Ran the Sumo11 test program (IC 5.09) with no motots
connected. With motor power switch off the led's light up in expected
sequence for the test. Turn on the motor power switch and the system
resets. I can get and replace the L293D. What else should I check/do?