I've never heard of testing SCRs. What do you do when you find the problem SCR. Do you replace the board, resolder new scr, replace whole drive?
What you do is up to you. What I do depends on a number of factors, but if a board is relatively easy to get an "iron" on, with out cooking other components, I'll do some component level repair. If it's something that requires a high level of availability, or is a real pain to swap I'll get a new board or a new drive.
As you may guess, I'm not a board level guru. I've found that sometimes the "bad" component I found, and replaced, died for a reason. That reason doesn't become evident (to me) until after some, post "fix", run time. If you aren't out anything trying to fix it yourself it's a good learning experience.
Doug S.