When evaluating an instrument for repairs, first carefully check all of the
joints in the body of the instrument.
The most frequent problem (very common) is that the wooden anchor pin block in the end of the autoharp will, over the years, come loose from the sides and back and start to twist out and upwards, following the strings on their way around to the top of the instrument.
This can be repaired adequately without removing the strings by first loosening all of the strings and then gluing all of the loose joints with a good quality thin slow-drying epoxy (such as West System 105 Resin and 205 Hardener). Common white and yellow wood glues are not a good choice for this joint because of a tendency to slide under stress.
Set up and test your clamping system first -- it is a bit difficult to get the parts to move back toward their proper locations. You will want to use leather padding under your clamping blocks where the strings cross over their bridge rail. Also take some care that you will not create problems for yourself with excess glue. The fact that you are trying to avoid the work of taking off the strings creates the real possibility of gluing some of them permanently into place, a scenario you want to avoid.
This method will not get the parts back into perfect alignment, but can accomplish an adequate and perfectly functional result. To get a better result, the strings would have to be removed and the joints completely loosened, so as to be able to realign the parts, and a new set of strings will have to be put on afterwards.
Often the top of the instrument will dish into the instrument. While this is
technically a problem, to fix it would require disassembly of the body
(removal of either the back or top), which would be a cost-prohibitive repair,
and in practice most autoharps go for many years in this condition without it
creating problems with playability, so it can usually be safely ignored.
What cannot be ignored is warpage of the body that results in the plane
of the strings not being flat. If a straightedge placed across the strings
shows the middle strings to be higher than the outer strings (the most
probable case), the bars will not damp all the strings evenly. The best
solution is not to buy an instrument that you find in this condition. With a
set of aluminum bars, it is
possible to bend the bars to conform to the real shape of the plane of the
strings and so salvage the instrument. It would be perfectly possible to
salvage an instrument with wooden bars as well, but the job would
require removal and replacement of the felts, and the amount of additional
work would be sufficient to make it cost prohibitive.
After checking the body for loose joints, play through all of the chords and
listen for problems with the felts while evaluating the feel of the bars for
any sticking or other problems they may present. If the instrument is out of
tune, it is more difficult to tell whether the felts are correct, but by going
slowly and carefully, one can usually detect any wrong strings sounding in a
chord. Check out the causes of any problems found.
Finally, note the following list of common problems, and check to see whether any of them are present on the instrument at hand.