I would think that it would be pretty easy to repair one. It's a pretty simple device. If you want to educate yourself why not purchase one of those 101 electric experiments kits and do some of those till you feel confident enough to go in and repair your devices? I'm not sure how you would test to see which piece has broken though.
I am assuming you are using this device daily which is why it's wearing out. Or are you using it several times a day? I hope you are also doing some cleansing of toxins from your body as it's all linked to your symptoms.
Dr. Hulda's book has the schematics for making your own zapper but it's very hard to follow. It crosses symbols comonly used in schematics with her own symbols. So if your used to schematics that might throw you and if your not you might be lost. My husband burned up the first one he made because of the way she wrote it. He now has design modifications he wants to make though:) The next one he makes gets a timer light and some other things.