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All excellent questions. You are right to be skeptical about a 100% failure rate, and your following that up with tests on a BF199 indict the test method more than the transistor.
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It's relevant to mention that many high-ft transistors have vey low breakdown voltages in inverted mode (i.e., collector and emitter exchanged). Depending on how those Chinese component testers do their analysis, it's possible that the transistor is actually driven into reverse avalanche breakdown, which could very well be (mis)interpreted by the tester's algorithm as a diode being present and forward-biased when the emitter voltage is above that of the collector. For grins, I tried some 5GHz microwave transistors (Toshiba 2SC3302) that are known good (my students use these by the bushel in the microwave circuits class I teach). They (the transistors, not the students) all behave the same on the Chinese component tester as the "bad" 151-0367-00 transistors. The tester insisted that these transistors had the infamous C-E diode. A standard DMM diode test does not show this diode, because the DMM's applied voltage is too low to provoke reverse breakdown. So, the tester is the problem, and not the transistor. Based on this set of results, an automatic "replace on sight" policy for these transistors based solely on a component tester's say-so seems unjustified, especially since the tester is most likely to make an error when evaluating possibly expensive high-ft devices. -- Cheers Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 9/13/2023 05:33, radiobero.bb@... wrote:
And this is where my doubt begins – |
