I'm a complete noob with these things so please bare with me 
I bought this to build an ambilight for my TV. I had it all working perfect following these instructions http://www.instructables.com/id/30-channel-LED-RGB-Ambilight-Clone/#step1 I got it all fit to the TV and set the LEDs going before I plugged the HDMI into the tele. I noticed a small spark on the HDMI and the LEDs suddenly cut off. I assume I somehow shorted something out. My question is how do I test the Arduino Duemilanove to see if I've killed it? It still shows on the serial port when i plug it in via USB and the board lights up, then I can upload the program no problem. I've already tested the LEDs to make sure they're not the fault, so it must be the Arduino Duemilanove or possibly the TLC5940 PWM Unit? Thanks for your patience in reading this far 
The tlc5940 seems to be sensitive to ESD. I have blown chips moving them from the tube to the circuit.
Thanks for the reply James. I managed to get my hands on a multi tester last night and found there was 5V coming from 2 of the pins and negative from the other (pins 9-11) cant remember which was which and what else I was getting from any others, I had a few drinks after that! I would guess that's a good sign that this is still working and most likely be the tlc5940's? Thanks again 
FrazK:
found there was 5V coming from 2 of the pins and negative from the other (pins 9-11)
Since you are testing in-circuit, you have to take the rest of the circuit into account.
The TLC5940 doesn't actually "output" a voltage. It acts as a current sink for LEDs. Each output will cause a voltage drop which varies to keep the amount of current it is sinking, constant. It is a very fancy resistor.
So if you measure 5V on a pin, that doesn't necessarily mean anything. However, there is no condition which would allow the output to drop (or measure) a negative voltage, unless your leads were reversed.