I am sorry for the trouble experienced with tuning the autoharp. I have always tuned mine sitting at the keyboard which is an acceptable way to tune the thing. It is a simple pitch-matching exercise which should take about 10 to 15 minutes at most.

With age, any of the strings can wear out. This is true of any stringed instrument guitar, violin, piano etc. Do be careful with piano strings that snap as they can be lethal.

Hope this helps.