Re: Diagnosing faulty Transistors with a Curve Tracer

Ed Breya
 

Do you mean that you can pull a transistor that's apparently failed in-circuit, and it tests out normal on the curve tracer, but if you put it back in, it still doesn't work? What happens if you pull it and test again afterwards?

One thing that can cause problems is degradation of the transistor's actual durability (SOA) versus the stress applied. Usually, SOA failure would be catastrophic in a power circuit, so the part would suffer permanent damage that would show in further testing, but maybe not, depending on the circuit. I assume you're talking about audio power amplifier applications, so the DC SOA curve is what counts. If you set up the curve tracer testing to push a questionable part to just below its specified or empirically determined SOA limits, or slightly above the estimated circuit conditions, it may show that something's going on.

Ed

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