The Principles of Operation guide (available on the kit’s documentation page: http://wiki.evilmadscientist.com/555 ), walks through how the 555 works in detail, and says what every component does. Without this detailed guide, you’ll likely find the schematic alone nearly useless for debugging.
Figure 1, the block diagram, shows the major parts of the 555 and how they are connected. Look further in for what constitutes each of those parts, and where their outputs are. Can you see a change in the output of the threshold comparator when you change the voltage on the threshold pin? Can you see a change in the output of the value of the trigger comparator when you change the voltage on the trigger pin? By asking these sorts of questions, you can narrow down exactly what parts of the circuit are working, and which are not. If you can’t get the LED to flash, then it sounds like the final output (at pin 3) is not working– but is it just the output circuit that is damaged (or not connected), or something before it?
