- Out of circuit: With an ohmmeter.
* resistance between collector and emitter should be high in both direction.
===> diodes are back to back in series (see also Fig. 2-3)
* reverse and forward resistance of emitter collector diode (reverse/forward ratio) should be more than 1000: 1 (silicon)
- In circuit: With a voltmeter
* measure VE and VC, the difference VE - VE should be more than 1V but less than VCC.
If VCE is less than 1V:
----> transistor may be shorted
If VCE equals VCC:
---- > transistor may be open
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