K4401 missing one sound

I just finished the k4401 Sound Generator kit with no trouble. Nice kit! It seems to work normally except for one sound is missing: the explosion. Key number 3 is supposed to trigger the sound, I hear nothing. All other sounds work OK, except button number 2, mortar and explosion. I get the mortar sound but the expected explosion is missing. Maybe this is due to the key 3 explosion not working.

If I press key 3 and then another key, there is a delay before anything works AS IF the key 3 was playing the explosion sound.

For trouble shooting steps, I re-flowed most of the solder connections and did a close inspection. During construction, I measured each component before installation.

Could a construction error cause one sound to fail?

Thank you in advance for your comments. -=bd=-

Check continuity of keyboard matrix.
If problem persists, return ยต-controller for test/replacement.

Thank you for the quick reply. I will carefully go over the board again. :neutral_face: