Zero volts means a short or open?

Discussion in 'General Electronics Chat' started by Billy Mayo, Apr 10, 2013.

  1. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    Fluke 87 specs:
    http://support.fluke.com/find-sales/Download/Asset/2161164_6116_ENG_B_W.PDF

    Seems like the highest is 5Khz for measure AC voltage


    Any reason why they want the power supply to be at a very high frequency?



    How would a Troubleshooting tech know if zero volts is an open component or a short component?

    Cause a short to ground can cause components to measure zero volts, but so can an open component cause components to measure zero volts

    So how would a troubleshooting rule out its an OPEN component? because of why


    What is it called when a diode is not open or shorted , but measures a voltage like .175 volts in reverse or forward biased? it's not called a short or an open, its called what?

    What is it called when a component is shorted or open in a network , stage or circuit that causes other components around it has altered it's voltage or/& resistance for there normal values when taking measurements?

    I see this a lot when I'm troubleshooting, when a component is shorted or open it alters the resistance values of resistors, capacitors values, voltages, but what is the name of this?
     
  2. YokoTsuno

    Member

    Jan 1, 2013
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    The datasheet of your DMM specifies 20kHz as upper range. That doesn't mean it stops working at 30kHz. It's probably less accurate (Most likely a lower reading). At a certain frequency readings become meaningless though.

    I assume you're talking about a switched mode power supply (SMPS). Higher frequencies mean smaller transformers and therefore smaller overall PCB and less weight.

    He or she wouldn't. It depends on the location and function of that component within its circuit. One needs to be able to read a schematic drawing. That's why technicians and engineers train for several years.

    It's probably called a real diode. Perfect diodes only exist in textbooks.

    Collateral damage maybe? I have to admit that my English has room for improvement.
     
  3. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    No,it's a zener diode at .7 volts normal at forward biased

    This Bad zener diode is .175 volts forward biased and reversed bias

    It's not a short and it's not an open, what is this called?
     
  4. gerty

    AAC Fanatic!

    Aug 30, 2007
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    How is it placed in the circuit, you're only giving us half the information . It's hard to give you a valid answer with little information given
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    And many components won't measure a correct value when "in circuit". Due to the components connected to them in the circuit.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If those values are measured out of circuit, then I would call it melted, dead, shot, or something similar.
     
  7. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    Yes the Diode is " out of circuit " it measure .175 volts forward biased and reversed biased what is this called ? its not a short or an open

    Yes I know the junctions are broken down in side, but its not called a short, leakage or an open, its called what?

    Also, what is this called when you get these types of "In circuit" measurements? it this circuit impendance's?

    When A component is shorted or open, it changes the "in circuit" measurements, what is it changing? the "in circuit" resistances change but is this called impedance?
     
  8. YokoTsuno

    Member

    Jan 1, 2013
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    If the DMM is in DIODE -|<|- mode and this is indeed a diode, it is shorted. A short is not always zero. In fact the failed diode might have a remaining resistance which result in a reading of 0.175. Watch this video. A diode that's working properly shows a reading of
    - around 0.5 - 0.7 when it's forward biased
    - OL when it is reverse biased

    No, you can look as impedance as a sort of resistance which only applies to AC, not DC.

    That's impossible to predict. Depends on the nature of the circuit and location of the failed component in the circuit.

    Good luck
     
  9. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    Yes true it does in DVM diode mode, but its measuring 0.175 in DVM diode mode in both direction

    A shorted diode means the continuity is 0.2 ohms , it's like a bare wire

    Open Diode, measures OL , overload on the DVM meter

    When the diode has its junctions broken and it is at .175 volts it's not a short or open its called something
     
  10. Billy Mayo

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    Mar 24, 2013
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    When using the DVM meter in ohms mode

    The resistor can be a 10K ohm out of circuit , but in circuit it can measure between any value

    When taking "in circuit" measurements , what is this resistance reading called?

    What I mean is it changes the resistance reading on the components around the shorted or open component, the resistance reading on my DVM meter has changed the " In circuit resistance?

    Is it just called the In circuit resistance?
     
  11. #12

    Expert

    Nov 30, 2010
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    Immediately after calling this, "in circuit resistance", it is usually called, "invalid".
    The resistance reading you get when measuring, "in circuit" is 1/(the sum of all conductance paths between those 2 points). It is usually very difficult to visualize all the conductance paths in both polarities, and you must do that to get any useful information. That is why, "in circuit" measurements are not often used. Only simple circuits or simple sections of larger circuits can provide useful information from in circuit measurements. Far more often than not, no useful information can be had from in circuit measurements. If in circuit measuring was really useful, we wouldn't be spending so much time unsoldering parts to measure them.
     
  12. YokoTsuno

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    Jan 1, 2013
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    Where did you learn that a shorted diode always has a reading of 0.2 Ohms?
    I guess you can call it that way.
     
  13. Billy Mayo

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    Mar 24, 2013
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    Because some diodes when they get shorted they are Beep on my continuity check

    Other diodes that are Partially shorted and reading a weird voltage forward biased and reversed biased , are partially shorted or leakage , but it's not a short because its not like a bare wire

    Some shorted diodes are like a bare wire , this is a short

    I'm talking about the partial shorted , from the junctions inside the diode are partially shorted

    What is this called?
     
  14. Billy Mayo

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    Mar 24, 2013
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    If you have a Golden Sample Good Working circuit , compared with 50 bad boards of the same circuit

    If you measure the "in circuits resistance value" for every component , compared to the Golden sample good working circuit

    Can this lead you to the problem or a short? can't this In circuit resistance give you information to lead to you the problem of a bad circuit?
     
  15. #12

    Expert

    Nov 30, 2010
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    Yes. Comparing a known good board will give you useful information. The problem is that nobody publishes the "in circuit" values for their circuits and most people don't have a Golden Sample for everything they work on. However, you are free to make lists of these measurements for yourself to use.

    and, a partial short is called a partial short.
     
  16. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    Can this lead me to a short circuit or an open circuit or a bad IC chip?
     
  17. YokoTsuno

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    Jan 1, 2013
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    That's an interesting analysis. Never saw that coming :rolleyes:.
    In the past people used signature analyzers (Like the HP5004) for fault finding which are based on the same school of thought. This only work for digital circuits though.
     
  18. #12

    Expert

    Nov 30, 2010
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    Yes, but it is like saying, "If I use a diving rod, a psychic, and a photograph, can I get the same results I would if I used a pencil, a paper, and a ruler?"

    Yes, sometimes you can, but, if you are smart enough to use that method, you are surely smart enough to measure and calculate like us common people.
     
  19. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    How would a Troubleshooting tech know if zero volts is an open component or a short component?

    Cause a short to ground can cause components to measure zero volts, but so can an open component cause components to measure zero volts

    What other "References" can I use?

    1.) Measuring reference to ground
    2.) Measuring Across the component
    3.)

    All the components in the Bad Stage are all measuring Zero Volts , Measuring referenced to ground and also measuring across the each component

    What else can I do to rule out its either a short or an open? cause it could be either a short or an open right?
     
  20. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    When I find an Open Resistor, 99% of the time it measure in the Meg ohms " In circuit " right? or reads OL overload on my DVM meter

    What have u guys seen , when you found an open component or an open resistor?
     
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