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Old 4th February 2013, 04:37 AM   #11
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Quote:
Originally Posted by Gyuri View Post
Thank you for your answer,
You know, I'm not an electronics expert.
If I'm thinking of it, I'm not an expert in anything.
Maybe I'm just an expert of suffering.
But would you do it for me, measure your DMM's diode measuring output voltages with each other?
I'm just curious.

Thanks,

Gyuri
I checked both of my Fluke 16's at home (a rather cheap DMM) and measured 2.66 V on one and 2.64 V on the other when in diode check. I have not checked the Fluke 87 in the lab yet. Both models were able to source adequate current to measure a cut-on voltage when I tried them with multiple parts. Other DMM's may read open if the leakage current with the available open circuit voltage is too low, at least that's my speculation. I'm assuming that if a meter has a diode check function, it was designed with 0.7 V in mind.
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Old 5th February 2013, 01:08 AM   #12
flg is offline flg  United States
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Thanks Semisouthfan.
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Old 5th February 2013, 11:01 AM   #13
generg is offline generg  Germany
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Thanks Semisouthfan!

good article!


I have three DMM at my house, all three did show "infinite resistance". So the fluke DMM must have another characteristic.....
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Old 5th February 2013, 12:48 PM   #14
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Originally Posted by generg View Post
Thanks Semisouthfan!

good article!


I have three DMM at my house, all three did show "infinite resistance". So the fluke DMM must have another characteristic.....
Thanks for the feedback. Your not the only one seeing this with your DMM's. Since diode checkers are not expecting such high built in potential, it's not surprising. Bias either junction with a power supply or battery in series with a resistor and that same DMM on a voltage setting will measure what the diode checker won't. When doing the measurement, say gate-to-source, leave the drain pin open (or if gate-to-drain, leave the source open). Again, thanks for relating your experience.
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Old 5th February 2013, 04:29 PM   #15
Blues is offline Blues  United States
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Some DMMs might not have a 9V battery supply like Fluke DMMs have. These lower battery supply DMMs typically can only measure 0.6V silicon diodes (or bjt pn junctions) or the now rare 0.3V germanium diodes/transistors.

Thanks for the article, Mike.
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Old 5th February 2013, 04:34 PM   #16
generg is offline generg  Germany
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very interesting Blues,

All my three DMMs have 9V supply....
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Old 5th February 2013, 05:23 PM   #17
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Quote:
Originally Posted by generg View Post
very interesting Blues,

All my three DMMs have 9V supply....
Quote:
Originally Posted by Blues View Post
Some DMMs might not have a 9V battery supply like Fluke DMMs have. These lower battery supply DMMs typically can only measure 0.6V silicon diodes (or bjt pn junctions) or the now rare 0.3V germanium diodes/transistors.

Thanks for the article, Mike.
I'll add to your list: Silicon Schottky barrier diodes which are not rare and cut on at about 0.3-0.4 V.
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Old 5th February 2013, 05:50 PM   #18
MRupp is offline MRupp  Germany
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My cheap DMMs do not measure anything but my peak atlas DCA55 component tester shows a "LED or diode junction" with some 2,50 volts from G-S or G-D. If I connect all three poles it shows a "faulty device" (I hope they are not ).
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Old 5th February 2013, 05:56 PM   #19
Blues is offline Blues  United States
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Quote:
Originally Posted by generg View Post
very interesting Blues,

All my three DMMs have 9V supply....
3 possibilities then, Gerd:

-Replace DMMs
-Replace fake/bad Jfets with genuine SS Jfets
-Both the above

Seriously, DMMs might not be designed for higher than typical 0.6V diode junctions -designer did not anticipate the coming of 2.6V SS jfets

Yes on the Schottkys too...
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Old 5th February 2013, 06:01 PM   #20
Zen Mod is offline Zen Mod  Serbia
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luckily - all Generg's SS are already tested in vivo

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