Connect with us

N Channel JFET Testing in ESR Tester

Discussion in 'General Electronics Discussion' started by SteveK, Sep 25, 2016.

Scroll to continue with content
  1. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    I am testing some MPF102 JFET'S in my ESR tester. four of them identified as "TWO DIODES". The last one identified properly as an N CHANNEL JFET. I'm not sure how to interpret these test results. Are the ones showing up as "TWO DIODES" defective? My ESR TESTER USES A MEGA 328 MICRO CONTROLLER. i've also tested a 2SK152-3 JFET which I believe to be blown and it identified as TWO RESISTORS. I believe THAT indication to be correct. Please correct me, if i'm wrong. Any help with this would be very much appreciated.
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    SteveK, welcome to EP.

    I don't know why you call it an "ESR" (Equivalent Series Resistance) Tester. That's only one parameter that these devices test. I own two (Atmega uC based) Component Testers. They've been evolving over the years. Unfortunately the two versions I have both report an MPF102 JFET to be a Resistor.

    I'm going to dig back through datasheets and documentation I have to confirm this but I believe the JFET is or was not a component that it could properly identify at the time of my purchase.

    This technology has been steadily evolving though. I believe that if the latest version doesn't include JFETs they soon will.

    Chris
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Here's some reading for you. In particular find "Measurement of JFET and D-MOS transistors" in the idex. BTW the author uses the word "deferred" when speaking of the Drain - Source terminals of the JFET. I believe it should read "differentiated".

    Chris
     

    Attached Files:

  4. HellasTechn

    HellasTechn

    1,544
    215
    Apr 14, 2013
    If the meter is like the ones sold on e-bay and gives you a 2 diodes reading then YES your FET's are BAD.
     
    Last edited: Sep 26, 2016
    SteveK likes this.
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    The models I have were both purchased on Ebay. The first one (MK-168) came enclosed in a plastic case that includes a 9V jack to power it off a wallwart if desired. It's LCD is an older model (smaller) with no graphic capabilities that uses ASCII art to depict components. This model is reporting that the MPF102 is a resistor network that displays it something like this (2)---[135.5Ω]---(1)---[29.7Ω]---(3). Of course it doesn't display an Ω symbol.

    The other model is a GM328A (V1.111) that's supposed to be a later model with a much nicer LGD. It is sold caseless. This model is reporting a single 29.7Ω resistor between pins 1 & 3.

    Not long ago we had a discussion about these testers. Steve (our moderator) owns a version. Hey Steve, what does yours diagnose for JFETs?

    Chris
     
    SteveK likes this.
  6. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Mine identifies an MPF102 as a single resistor.

    Bob
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Thanks for your observations Bob. What do you think is a reasonable timeline that these testers will properly identify JFETs. I'm betting within a year.

    Chris
     
  8. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    Hi Chris,
    i only recently discovered this device(ESR Tester). A month ago, I never knew it existed. All the listings that I see for this device almost always refer to it as an ESR Tester. So, I accepted that term. If i'm not mistaken, it was originally meant to test primarily Capacitors. please correct me on that if I'm wrong. Today, I tested 5 2SK715W JFET'S. They all identified properly. O, btw, thank you for the reading material.

    Steve
     
  9. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    Hi Constantine,
    Yes, got it on Ebay. Paid about 13 bucks for it.

    Steve
     
    Last edited: Sep 27, 2016
  10. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    Hi Chris,
    Mine indicates for as an example, for a 2SK715W, I=0.81ma and Vgs=0.57V. as well as the Pinout with GSD identified.
    For one of my MPF-102's, shows a Diode between 1-3 and 2-3.
    I tested a 2SK152-3 which identified as 2 Resistors.
    Mine uses a 328 Chip. I'm not sure of the firmware version.
    Steve
     
    Last edited: Sep 27, 2016
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,449
    2,809
    Jan 21, 2010
    It really depends on how good the tester is. maybe the "two diodes" have low tra

    When I'm closer to home. I'm over 5000km (that's 2 states) away by road at the moment. Hard to get to the shed at the moment :)
     
  12. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Two states away, 5000Km? Here in Massachusetts, 2 states away is about 150Km :)

    Bob
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,449
    2,809
    Jan 21, 2010
    Yeah, I cheated a bit. There's no direct road route. it's only 3450km as the crow flies. It's not quite the two most distant points in the country, but it's pretty close!
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    The history of the device is included in the PDF file I posted. The author released his schematics and source code to SourceForge as freeware years ago. He's also well aware of the existence of the many Chinese clones.

    Chris
     
  15. HellasTechn

    HellasTechn

    1,544
    215
    Apr 14, 2013
    Yes that's how most sellers on e-bay call it.
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Well its author/designer calls it a Transistor Tester, which it is and as he modestly states " and a little more". Personally, I think it qualifies as an invention because I know of no other device that automatically finds the pinout and device family of 2 & 3 pin solid state devices. At least not one that the average electronics enthusiast could afford.

    Chris
     
  17. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    Actually, it does (to me anyway) a lot more! A very handy little "toy". I just received an order of 2SK345, and 2SK291 JFET'S. I was curious so I tested each type (5 of each) to see if they would identify correctly. Every one correctly identified. It really is a great little "gadget".
    Steve
     
  18. SteveK

    SteveK

    19
    0
    Sep 25, 2016
    And Chris, your right! You can install the FET backwards, it figures out the pin out and displays the result, VERY NICE!!
    Steve
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    That's a primary feature. There is NO correct or incorrect connection to the tester. Any 3 pin device (that it's capable of testing) can be connected to it in any pin-out orientation. The uC analyzes the device under test and determines which device pin is connected to each of the three tester input terminals. You can mix and match the way you connected it and it will sort it out regardless of which device pin is connected to which tester pin.

    Chris
     
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    I found this during a Google search.
    http://socrates.berkeley.edu/~phylabs/bsc/PDFFiles/bsc4.pdf
    It's from Berkeley, so it's quite thorough. Though I'm surprised that within this document I didn't see any reference to the Drain / Source ambiguity encountered when determining the pin-out of JFETs.

    If and when these Atemega or other uC based testers can properly analyze them I would imagine that a negative source (for Gate / Source bias) would be required. Even with that, JFETs may confuse the hell out the tester as this simulation demonstrates.

    Check out the Drain / Source hookup between these two circuits. I inverted Q2 connecting the named pin "Source" to V+ and the named pin "Drain" to (-) GND. As you can see in these (Vg vs Ids) plots they're identical when wired either way.

    The schematic symbol of the JFET in itself provides a clue to it's ambidextrous Drain / Source properties, as it's not differentiated symbolically.

    Chris
    upload_2016-9-30_10-17-10.png
     
    Last edited: Sep 30, 2016
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-