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-   -   Is there any quick method to measure if a jfet is dead? (http://www.diyaudio.com/forums/solid-state/173011-there-any-quick-method-measure-if-jfet-dead.html)

Sunsun22 3rd September 2010 06:27 PM

Is there any quick method to measure if a jfet is dead?
 
As titled, I have a batch of old jfets and need a quick method to know if any of them were dead other than using the usual Idss jig.

Thanks

jacco vermeulen 3rd September 2010 06:29 PM

Connect them as a diode.

chlorofille 3rd September 2010 07:27 PM

Check for a short circuit between gate and drain...

Sunsun22 13th October 2010 12:59 PM

If I can measure Idss on the jfet, does it mean it is working?

andyr 26th November 2010 07:38 PM

Quote:

Originally Posted by chlorofille (Post 2292641)
Check for a short circuit between gate and drain...

I have the same problem as the OP about whether or not some JFETs are "dead", so your answer is very much of interest. :)

OK, so I check for a short between gate and drain - so if there is a short, it's blown, right?

Or does a short mean that it's OK?

If there isn't a short, does that mean the JFET is OK? Or are there other easy tests that can be done?

I have heard that JFETs are very susceptible to being zapped from static. If this happens, what sysmptoms would a JFET display?

Thanks,

Andy

Bigun 26th November 2010 08:26 PM

Quote:

Originally Posted by andyr (Post 2377949)
I have heard that JFETs are very susceptible to being zapped from static.

Generally, I don't believe JFETs are static sensitive to anywhere near the degree of MOSFETs - they are pn junction devices with no thin gate oxide to worry about. You'd need an impressive amount of static to kill a JFET.

andyr 26th November 2010 08:43 PM

Quote:

Originally Posted by Bigun (Post 2377992)
Generally, I don't believe JFETs are static sensitive to anywhere near the degree of MOSFETs - they are pn junction devices with no thin gate oxide to worry about. You'd need an impressive amount of static to kill a JFET.

Ah, thank you bigun. That is good to know.

My problem is that I have soldered in a couple of JFETs and am getting a 0v reading from Drain to Source. So I am wondering why - it seemed to me that:
a) I might have got the pins wrong?
b) it might have been blown before I soldered it in place?
c) I might've zapped it with static?

So, as we can eliminate c), it seems likely I might have got the pins wrong? :o

The JFETs are MPF102s. There is a cursive 'f' on the flat side - so I have assumed it must be a Fairchild, hence the pins are (from L to R, with pins down and looking at the flat side) D S G.

Do you know whether this is correct? :confused:

Regards,

Andy

AKSA 26th November 2010 08:48 PM

1 Attachment(s)
Andy,

You might have the D and the S interchanged?

No, I'm wrong, you are right, here's the pinout from the Fairchild pdf, all is correct!

Hugh

Attachment 198163

andyr 26th November 2010 08:54 PM

Quote:

Originally Posted by AKSA (Post 2378007)
Andy,

You might have the D and the S interchanged?

I will check the datasheet,

Hugh

Thanks, Hugh. :)

andyr 26th November 2010 11:48 PM

Quote:

Originally Posted by AKSA (Post 2378007)
Andy,

You might have the D and the S interchanged?

No, I'm wrong, you are right, here's the pinout from the Fairchild pdf, all is correct!

Hugh

Attachment 198163

I thought I had used the correct pin connections! :) So why am I getting a 0v reading? :confused: :confused:

I will replace the ones I have soldered in with some fresh ones ... as it looks like they are kaput! :( Trouble is, perhaps the whole batch I was sent (16) is all kaput? I need to be able to test them before I go to the trouble of soldering them in.

Would measuring the Idss first, "prove" they were OK?

Regards,

Andy


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