Hi Peter,
Sorry to hear about your misfortune. I have two working DC boards here, which I used with a couple of different DC motors. Could you let me know what motor you tested the board with? While testing I put two 1 Ohm resistors in parallel to create a 0.5 ohm sense resistor in the power line to the driver board. This allowed me to do some rudimentary current measurement during the tests. I never used full power to the board, but at most a PWM ratio of 200/255. My fear was more for the motor than the board, as it was a 4.5V-6V motor.
I used a 7.5 V wall wart instead of a 12V PC supply. I could see how at 12V the motor could draw too much current for this relatively puny driver board. Probably it would be just a matter of plugging in a new chip for you, but otherwise you could make me an offer for an assembled and tested DC driver board
-Geert