Ampeg svt 4 pro unidentified transistor

[Bigdrums]

FOUND A SLIGHTLY BURNT AND SHORTED TRANSISTOR. Fairchild j17g. Is anyone familiar with this? Can find almost nothing online. Its a TO-83 I think I did find some at alldatasheet.com referring to it as a "grade 5 ingress protection"

[g1]

What is TO-83 package? J17x would be a jfet if the x was another number (not g).
What is it's designation on the schematic, and can you post schematic?

[TomCarlos]

Might that be a Fairchild J176? Maybe Q101 on Page 1?

svt4_pro_amp.pdf

[Bigdrums]

Both of you are correct, its a TO-92 sorry about that and yes it's a J176 not G. Sure looked like a G to me THANKS!

[x-pro]

This transistor J176 is p-channel. It can be read as shorted at the drain and source. That's normal.

[Bigdrums]

It is shorted across all 3 legs

[g1]

It is shorted across all 3 legs

Sounds like it's shot. Replace it.

[Bigdrums]

I curious, do you guys look up the data sheets each time to know which is the drain, source and gate, or is there a simpler way to know that?

[x-pro]

I'll answer with a question.
How often does a builder look at documentation and drawings to build the house you will live in?

[nevetslab]

I curious, do you guys look up the data sheets each time to know which is the drain, source and gate, or is there a simpler way to know that?

Often (in the case of J112 NPN, the right hand lead is the Gate, the Center Lead is Source and left-hand lead is Drain. The J174-J176 family has the Gate in the middle, Left hand lead is Drain, right-hand lead is Source. I usually have to look at the data sheet to see which is Drain and Source, but easy to find (from a basic functional state) looking to see that it measures semiconductor junctions from the Gate to the other two leads with an ohm meter. That will tell you whether its' a P-Ch or N-Ch, and that you have readings between gate, drain and source, or shorts.

[The Dude]

I curious, do you guys look up the data sheets each time to know which is the drain, source and gate, or is there a simpler way to know that?

If I'm replacing a transistor with an exact replacement, I usually just orient the replacement the same as the original. If I'm using a cross-referenced or substitute part, I will always check the datasheet for proper orientation.

[g1]

With experience, you can often figure it out without having to look up the pinout. But it depends how much you need to know.
Can you figure out the E,B, and C of a transistor without looking it up, and whether it is NPN or PNP? I could mostly do that but couldn't differentiate between E and C til I learned that the B-E junction always reads a bit higher than B-C.
With the jfets we use, you will find that S to D usually reads low resistance. From there, the other pin will be the gate. If I need to know more than that, I look it up.

[The Dude]

Yes, I use that method too, sometimes. That used to be quicker than finding a datasheet when datasheets were paper. Now that we have the internet, you can find a datasheet with a few keystrokes. But, either way works.