Thyrister Testing

Well, I would have thought a telephone call to the equipment manufacturer would be the first step. Then, I'm funny that way.

That information is contained in the specifications for the specific part number.

Without a specific part number and manufacturer we can't do the hard work of looking up the specification for you. I don't know how we ever got along without the internet before 1995. But then, I can't remember much about highschool either.

I don't know how we ever got along without the internet before 1995.

They were called books, were very thick, expensive and filled with almost everything you needed (although the search function was fairly primitive)

Fortunately the books are not dead they live on and many are accessible on the internet now for free. One of my personal favorates regarding SCR design and application is the following 674 page monster.

http://www.scribd.com/doc/196710069/SCR-Triac-Theory-Data

Testing an SCR will depend on the type of SCR. "Hockey Puck" style SCRs can only be tested when clamped under pressure as they would be in their heat sink assemblies. Smaller SCRs that are either stand alone or in anti-parallel "brick packs" can be tested outside of the heat sink assembly.

Once you establish the method, then just measure resistance across them. Anything less than 10k ohms indicates a shorted SCR. You can also test the gate with an ohmmeter, the correct value varies by design, but failure of the gate without failure of the main substrate is exceedingly rare.

Designing a firing circuit is not a "tip", it is a course, and for it to be meaningful, you need to fully understand the application. For example firing a 2A rated 240V SCR to be used as a ramped rectifier is very different firing method from firing a 5kV 400A rated SCR in a medium voltage soft starter. There are almost as many firing schemes as there are applications.