What is the expected resistance of a transistor in cutoff mode?

[Harrison G]

Homework Statement

Hi! I learned how to work with transistors a long time ago. However, it is good to fortify youre knowledge. I was checking a circuit board for issues and found a npn bjt, which Colector-emitter resistance while in cutoff mode, is arround 1k ohms. So my knowledge of bjt's says me that that is a pretty low resistance for a transistor in cutoff mode (it should be almost infinite). I mean, that thing is damaged for sure, right?

Homework Equations

The Attempt at a Solution

 

[Tom.G]

Probably... depends on how you "measured" it.

Most accurate of course is out-of-circuit with a transistor tester.
Out-of-circuit again, a few ohmmeter tests will usually spot a bad one. First, check that the junctions are actually diodes, that Collector-Emitter are not shorted, check Base-Emitter when forward biased then short Collector to Base and the indicated resistance should drop slightly.

In-circuit is tough because you have to account for EVERY component that the transistor is connected to, and if the circuit is powered-up you also have to take into account any signal present and even if there is a parasitic oscillation throwing the measurements off.

Have fun!

 

[Harrison G]

Probably... depends on how you "measured" it.

Most accurate of course is out-of-circuit with a transistor tester.
Out-of-circuit again, a few ohmmeter tests will usually spot a bad one. First, check that the junctions are actually diodes, that Collector-Emitter are not shorted, check Base-Emitter when forward biased then short Collector to Base and the indicated resistance should drop slightly.

In-circuit is tough because you have to account for EVERY component that the transistor is connected to, and if the circuit is powered-up you also have to take into account any signal present and even if there is a parasitic oscillation throwing the measurements off.

Have fun!

Thank you :-)

 

[rude man]

Homework Statement

Hi! I learned how to work with transistors a long time ago. However, it is good to fortify your knowledge. I was checking a circuit board for issues and found a npn bjt, with collector-emitter resistance while in cutoff mode, is around 1k ohms. So my knowledge of bjt's says me that that is a pretty low resistance for a transistor in cutoff mode (it should be almost infinite). I mean, that thing is damaged for sure, right?

Homework Equations

The Attempt at a Solution

How did you determine the collector-emitter resistance? Include details such as powered-on or not, instrumentation, schematic, etc.

 

[Harrison G]

Thank you everyone for the replies, but the situation is already under control :-)