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Voltage Reading Not Accurate

  • Geddy Sunday, February 12, 2017 1:19 PM Reply

    Voltage reading is always less than 0.2V of the actual voltage.

    Example:  Actual voltage = 14.0V, reading = 13.8V

    No calibration adjustment POT inside the unit.

    Anyone know which resistor to change?

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  • sheepish Top 10 Forum Poster Sunday, February 12, 2017 6:10 PM Reply

    @desolder is your best chance.

    DX has found a new way to deceive customers:
    Use reviews for different products that have not been bought
    by the person who wrote the review.
    http://club.dx.com/forums/forums.dx/threadid.1462252
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  • ladroop Sunday, February 12, 2017 9:50 PM Reply

    The only thing you can check , does the voltage drop if you put a load on the USB.

    If it does you can think of a bad/dirty contact or maybe the fuse.

    And do you mesure your voltage on exactly the same place ?


    You may take a look at vst-e.com/vst706-p-169.html but are a bit down for me


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  • Geddy Monday, February 13, 2017 12:14 AM Reply

    No load bench test with fuse removed (direct connection to spring inside).  Same results at different voltage levels.  The voltage reading is always less than 0.2V of actual.

    Equipment used:  Rigol DP832 digital power supply, Fluke 87III, Fluke 117, BM235.


    Unable to load vst-e.com


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    post edited by Geddy on 2/13/2017 at 12:16 AM
  • sheepish Top 10 Forum Poster Monday, February 13, 2017 8:42 AM Reply

    The only thing you can check , does the voltage drop if you put a load on the USB.

    If it does you can think of a bad/dirty contact or maybe the fuse.


    {Cough.} Or internal resistance of the source.

    DX has found a new way to deceive customers:
    Use reviews for different products that have not been bought
    by the person who wrote the review.
    http://club.dx.com/forums/forums.dx/threadid.1462252
    Posts(22750) | Reviews | Tip post

  • desolder Top 10 Forum Poster Wednesday, February 22, 2017 1:25 AM Reply

    Often the voltage will be divided down then compared to a reference voltage (1.2V is common). Can you open up the unit and tell us what ICs are used? You can tweak the reading by adjusting the voltage divider.

    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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  • Geddy Thursday, February 23, 2017 10:32 AM Reply

    The IC markings are scratched off. :-(

    I added 100R in series with the 10K resistor R3 and now the readings are bang on.

    "Q.C. PASSED 202"  LOL


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