Have searched your local are for repair shops, supply houses? If you go there you might be able to find out how they learned or get some advice on a general area to look. Have you tried the internet? If you will find the website for the particular manufacturer, they generaly have manuals on how to trouble check and repair their machines. Your first post is asking about mig and tig machines so a basic knowledge of electrical systems will be a must ( I would think). Hope this helps I wish I could help some more.

P.S. You also can search this site there are several post dealing with these machines. Also look at local trade schools.