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Having negative reading with 2 DMMs !!

Discussion in 'Troubleshooting and Repair' started by Elecbegginner, Jul 22, 2013.

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  1. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    Hello everyone .

    I have two measurement tools , one for multi-purpose and one witch is a MEGOHMETER .
    The megaohmmeter (Chauvin arnoux 6547) shows twoo readings normally , one is the DC voltage and bellow a reading for the resistance .
    When i turn on the device , i get about - 4700 vdc witch should be just none , for the resistance its normal i dont have reading since i have not realised any measurement yet .
    For the DMM ( Uni-trend UT33C ) i have noticed a burn in the motherboard , replaced a resistance about 9 ohms with a jumper , fixed the burned switch crossing paths , but i have a -1 in almost any selection , am wandering if it could be from the jumper i made :confused:.

    Here are some pictures for the devices .

    [​IMG]
    [​IMG]
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    show us a photo of the repair you made to the DMM

    Dave
     
  3. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    I will do it for sure
     
  4. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    Ok hre is the picture with arrows
    arrow 1 indicates the fixed path
    arrow 2 indicates the burned path that goes to the resistance
    arrow 3 indicates the jumper i did as a replacement for the 9 ohm resistance
    [​IMG]
     
  5. Elecbegginner

    Elecbegginner

    103
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    Mar 24, 2013
    I hop thats clear
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    The roundabout looks like a gold plated switch pattern and will be mated with a dozen wipers.

    You have put blobs of solder on this - bad news.
     
  7. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    Even with blobs the switch goes very well on the paths , the problem is that negative -1 i get , could it be from the micro-controller ?
    Its not gold lol , its just the reflection of light that gives it that color
     
    Last edited: Jul 23, 2013
  8. eKretz

    eKretz

    251
    27
    Apr 8, 2013
    Regardless of whether or not it's gold, it IS plated, and that's what duke is trying to tell you. The tracks are very thin, and when you put a blob of solder on the track it forces the wiper up and may well damage the wiper's contact surface over time. So he was warning you that your repair is not a good one, and may well end up taking your switch out over time.
     
  9. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    yup exactly.
    and its probably at least one of the reasons that the meter isn't reading correctly

    you really cannot get away with rough repairs like that. its just making a mess of things

    Dave
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    In the short term, I would guess that whatever vaporized the tracks also damaged something else in the meter.
     
  11. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    Ok i see , is there any way to recover the tracks like the original way ?
     
  12. davenn

    davenn Moderator

    13,833
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    Sep 5, 2009
    no not really ... cheaper to buy a replacement meter.
    super cheap on eBay

    Dave
     
  13. Elecbegginner

    Elecbegginner

    103
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    Mar 24, 2013
    What about the megohmeter it cost about 2000 $ , am trying my best to repair it , with allyour help mates i may succeed for sure .
     
  14. davenn

    davenn Moderator

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    Sep 5, 2009
    its probably not going to be repaired without a service manual and being such a hi-tech
    bit of kit its more likely it will need to go to the appropriate service centre which will have
    the manual.
    The chances of repairing it at home are pretty low, and without good service info you
    are likely to cause more damage to it than what it is already suffering.

    Dave
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Several suggestions:

    1) Get a service manual
    2) Tell us how it was damaged
    3) Remember that these units can have seriously high voltages inside them.
     
  16. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    Sorry for being late , i got the service manual for it .
    Here is the link for the information : http://www.chauvin-arnoux.com.tr/dosyalar/site_resim/urunler/urundosya/2216553.pdf

    After reading quite a bit about the issue i got , the device acts like its already having a voltage applied , but whats weard is that the voltage is negative .

    Any ways i hope the service manual can give you a clear look at the issue .!!
     
    Last edited: Jul 26, 2013
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That's a user manual, not a service manual.

    A service manual tells you how to check for faults, not how to use the device.
     
  18. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    and further to what steve said...

    it will have circuit diagrams of the device.
    it will have detailed information on how the various sections of the device work
    it may even have flow charts that aid in fault finding

    Dave
     
  19. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    My bad luck , i have succeeded to contact the repair service for the megohmeter , asked for a copy of the service manual , and they said its prohibited to send it online ,

    I think i will open it an see my self
     
  20. Elecbegginner

    Elecbegginner

    103
    0
    Mar 24, 2013
    After a long research on the net i found that the problem was from an analog to digital converter "8716UB" , it was faulty and causing bad reading on the megohmmeter .
     
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