Intermittent problems are most often bad or cracked solder joints. You can try heating or freezing the are to test for that.

 

Intermittent problems are most often bad or cracked solder joints. You can try heating or freezing the are to test for that.

Yes but i'm trying to test the "switching" of the transistor, how can i test the internal toggling and switching of the transistor

I would like to test the transistor one by one like this, but how can I?

 

You would usually check for combination two things: Is it suposed to be on? and Is it turned on?
You need to look at the particular circuit and see how to check those two things at the same time.

 

What can I use to "enable" the transistor?

Some transistors switches are pull down switches and others are pull up switches. So what can I use to "enable" the transistor to cause it to switch?

 

You measure the v B-E voltage, or even beter if you can the base current.

 

If I tied a variable pot to +VCC and make a voltage divider and put the wiper on the base. I adjust the wiper of the pot until i find the threshold point of the transistor to switch states. I can monitor the switching state of the transistor using an analog meter or oscilloscope. The huntron has a DC generator so i can Enable the base to the transistor and monitor the switching off and on signature on the huntron.

 

Fact is, that is not a failure mode of transistors. They short,become noisy, or just die in general.

Still doing aircraft maintenance?

 

If I tied a variable pot to +VCC and make a voltage divider and put the wiper on the base. I adjust the wiper of the pot until i find the threshold point of the transistor to switch states. I can monitor the switching state of the transistor using an analog meter or oscilloscope. The huntron has a DC generator so i can Enable the base to the transistor and monitor the switching off and on signature on the huntron.

That is not going to work. The change in base voltage is very small, and without a known load completely useless.
You need to be able to decide whether a small signal or switching tranistor is ok or not without taking it out of the circuit. If you can not, then simply take it out and replace.
That is unless your wage is less than the time spent repairing times the price of the transistor, otherwise fiddle around as much as you please.

 

So I need an external current source circuit to enable the transistor to switch?

What can I use as an external current source circuit?

 

That depends. If you have the transistor in circuit, then just measure what is available to you. You might be able to provide some base current externally into a live circuit, but you might also destroy stuff in the process.
If you have the transistor out of circuit then do whatever tests you please.

 

Yes but i'm trying to test the "switching" of the transistor, how can i test the internal toggling and switching of the transistor

If you can force the circuit the transistor is in to toggle it, you simply measure the voltage at the three terminals, starting with the collector (if it's a grounded emitter switch). It should be straightforward to determine if it's working correctly.

If you can't force (or wait for) the circuit to turn on the transistor, you might be able to drive the base (assuming it's a grounded emitter NPN) with some nominal voltage through a resistor applied to the base. You have to study the circuit to determine whether this will cause problems.

There are few short cuts to real troubleshooting. You have to determine what measurements you have available and make the best use of them. You're not truely a technician or engineer until you've mastered troubleshooting skills.