I put together the Larson Scanner last night, and am not getting any action from the LEDs. I’ve determined that the batteries aren’t dead, because the terminal connections are measuring just over 3 volts. All of the resistors are showing around 1.7 volts as well.
Check that the IC is oriented the correct direction. Check that the IC is not getting hot.
Check that you have ~3V (logical high) at pin 1 (reset) and pin 20 (Vcc). Check that no two of your pins are shorted together (solder bridges, etc.).
Check that you haven’t reversed the LEDs: Your kit should have a spare LED in it. With power on, touch its leads to the leads of one of the LEDs on the PCB, on the back side. Try both orientations, see if it lights.