A lady friend of mine who performs regularly at our club has a Yamaha guitar, about 30 years old. Not satisfied with its sound of late, she asked the advice of an instrument repair guy who told her that, in his opinion, the truss rod had broken, or was in some way defunct.
Can anyone tell me the possibility of this problem being corrected by someone other than an expert? She doesn't want to pay out a small fortune for a repair, so could it be done by me, who has engineering skills, a certain amount of technical knowledge a steady hand and patience?
What's the odds of making a satisfactory job without ruining the instrument?
All advice appreciated.

Regards

Andy