Blown power transistor?

[AndrewT]

Hi,
I have just removed what I thought was a blown medium power transistor (MJE15033).

I have used my DMM set to PNP and measured the gain.
hFE =130. Testing currents unknown.

Does this mean the transistor is OK?
or should my testing be more thorough?

[BWRX]

Does the hfe you measured fall within the range that it should be?

The fact that you can measure any gain at all indicates that both emitter-base and collector-base junctions are ok at the test currents.

You can check the emitter-base and collector base junction voltages.

[AndrewT]

Hi,

check the emitter-base and collector base junction voltages

using a second DMM while the transistor is being hFE measured?

The range of hFE is 100 upwards for Ic=100mA and 500mA. and the graph shows only a slight slope at lower currents.

[BWRX]

Originally posted by AndrewT
Hi, using a second DMM while the transistor is being hFE measured?

Sorry for the vague response. I mean use the diode tester function on your multimeter to check the voltage drops across the pn junctions just as you would any other diode. You should see the usual 0.6-0.7V.

It sounds like your transistor is fine.

[MikeBettinger]

Hi Andrew,

The problem with transistor testers is they don't place any appreciable load on the transistor being tested and I've had numerous experiences where a transistor tested fine but would open up under a load.

There is not much information to go on here but I think a few in circuit checks for Vbe and current through what ever the load is might be a bit more of an indicator as to whether or not the transistor is functioning properly.


Mike.

[AndrewT]

Hi Mike,
you are suggesting a manual hFE test at a variety of Ic.

Easy to set up.

[MikeBettinger]

Originally posted by AndrewT
Hi Mike,
you are suggesting a manual hFE test at a variety of Ic.

Easy to set up.

Hi Andrew,

I am suggesting you test it in circuit but I'm unsure of what I'm commenting on.
What kind of problem you're experiencing? Is your circuit not functioning or is it not performing to expectations?

Mike

[AndrewT]

Hi Mike,
it's the pass transistor of the scaleable regulator GB
http://www.delta-audio.com/PSU_TWO/P...er_2.2_SCH.pdf

Since it's already removed and new passQ fitted I'll test it off board.

[anatech]

Hi Andrew,
I like using the Heathkit IT-18 the most. It gives you gain, C-E leakage and C-B leakage. It's not the most exact, but it's the best I have for service. It catches most defects. It is great at confirming signal transistor matches (match cal point).

To find an intermittent, heat the part up. Often on a defective part the hFE will suddenly drop (part goes open). I've had a couple start conducting beyond what is normal as well.

-Chris