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Old 3rd September 2010, 07:27 PM   #1
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Default 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.

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Old 3rd September 2010, 07:29 PM   #2
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Connect them as a diode.
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Old 3rd September 2010, 08:27 PM   #3
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Check for a short circuit between gate and drain...
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Old 13th October 2010, 01:59 PM   #4
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If I can measure Idss on the jfet, does it mean it is working?
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Old 26th November 2010, 08:38 PM   #5
andyr is offline andyr  Australia
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Quote:
Originally Posted by chlorofille View Post
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
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Old 26th November 2010, 09:26 PM   #6
Bigun is offline Bigun  Canada
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Originally Posted by andyr View Post
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.
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Old 26th November 2010, 09:43 PM   #7
andyr is offline andyr  Australia
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Originally Posted by Bigun View Post
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?

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?

Regards,

Andy
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Old 26th November 2010, 09:48 PM   #8
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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

MPF102pinout.gif
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Last edited by AKSA; 26th November 2010 at 09:55 PM.
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Old 26th November 2010, 09:54 PM   #9
andyr is offline andyr  Australia
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Quote:
Originally Posted by AKSA View Post
Andy,

You might have the D and the S interchanged?

I will check the datasheet,

Hugh
Thanks, Hugh.
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Old 27th November 2010, 12:48 AM   #10
andyr is offline andyr  Australia
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Quote:
Originally Posted by AKSA View Post
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?

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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