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Discussion in 'Troubleshooting and Repair' started by Jimmie, Jan 6, 2016.

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  1. Jimmie

    Jimmie

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    Jan 6, 2016
    I have a Micronta 22-210 Mulitmeter that works on all functions except AC. Check battiers and. fuse OK .Need help.
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    Hey jimmie,
    Have a look on youtube for EEVBLOG.
    There is a video on his channel showing the input components on most meters. Might help you!
    If you cannot find it, I'll find it and link to it.

    Martin
     
  3. shrtrnd

    shrtrnd

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    Jan 15, 2010
    After checking Martaine2005's advice, if you have any troubleshooting skills open the case up and look for burned components.
    A lot of DVM's I've worked on have a resistor at the V input jack to limit high voltage current for readings. That resistor is prone to burn-up at overvoltage.
     
    Last edited: Jan 7, 2016
    Martaine2005 likes this.
  4. Jimmie

    Jimmie

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    Jan 6, 2016
     
  5. Martaine2005

    Martaine2005

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    May 12, 2015
    Was that a reply?:p
    It's probably the resistor as shrtrnd suggested or a MOV. If somebody tried to measure continuity on a live circuit or something similar.
    I have the Tandy version (Eagle) still complete with box too.

    Martin
     
  6. 73's de Edd

    73's de Edd

    2,872
    1,216
    Aug 21, 2015

    .


    Sir Jimmie . . . . .

    If all of the other functions are OK on that Simpson "wanna be ", then compare its components against the schema below and see what might be bad along
    the GREEN ARROW path of the AC function of the unit.



    [​IMG]


    73's de Edd


    .
     
  7. Jimmie

    Jimmie

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    Jan 6, 2016
    THANKS for the replys. and theSchematic.
     
  8. Jimmie

    Jimmie

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    Jan 6, 2016
     
  9. Jimmie

    Jimmie

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    Jan 6, 2016
    There is a Varistor near the V input jack. its not burned up. If it was would not the other functions still work?
     
  10. shrtrnd

    shrtrnd

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    Jan 15, 2010
    You've got a open circuit in there somewhere. You just need to track it down.
    How do the traces look to your switching functions? Any damage on the printed circuit board trace?
    Varistors (if your meter has one) are used to absorb momentary voltage spikes. Typically if they fail they explode.
    I'm still figuring one of your resistors probably gave out (though I could be wrong, that's the most likely failure, causing an open circuit)
    Look at them with a magnifying glass. The newer resistors often burn or crack at the failure point.
    I know this is aggravating to look for, but the fact that you've only lost one DVM function would seem promising to me.
    Find what's causing that open circuit.
     
  11. uche

    uche

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    Jan 11, 2016
    It's advised u use your voltage tester separately from the voltmeter cause high voltage chars the resistors And variables.
     
  12. elebish

    elebish

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    Aug 16, 2013
    Your voltmeter does not measure ac, it converts the ac to dc and measures it. So, look for a diode in the circuit and check it. It should measure .5 to .7 ohms with the negative lead connected to the banded (cathode) end. May have to disconnect one end of the diode first. If your measurement instrument does not have a diode position, use the 2k ohm position. One more point: These dmm's are so cheap to buy, you might want to but a new one instead. But, I'm like you, I would rather fix the old one just for the fun of it. Ed.
     
  13. Jimmie

    Jimmie

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    Jan 6, 2016
     
  14. Jimmie

    Jimmie

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    Jan 6, 2016
     
  15. Jimmie

    Jimmie

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    Jan 6, 2016
    It was a diode 1N4448 that was causing the problem. Change it with a new one. Now the AC works fine. Thanks to your schematic I found the cause.
     
  16. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Good work elebish.
    Thanks for not giving-up Jimmie.
    It's disappointing to hear other people throw in the towel without trying.
     
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