LeRoy Olson told Popular Mechanics (November, 1928, page 129) what is wrong when a uke doesn’t sound right, and offered some advice (a little blunt at times) on fixing it:
Loose pegs, defective strings, frets not accurately placed, or nut too high from the fingerboard.
Common [wooden] pegs are likely to slip after having been used a number of times; they can be enlarged by boiling them in water. If the pegs are of the non-slip style and will not work, the threads are stripped.
There is only one way to remedy defective strings and that is to buy new ones. If any frets are a thousandth of an inch out of place, discords often will be produced. This defect cannot be remedied.
If the nut is too high from the fingerboard, the strings, when pressed, will give sharp notes. It will be found that if the nut is filed down and new notches put in so that the strings are only a small fraction of an inch above the frets–but be sure they do not touch–an improvement in the tone production will be noted.