current shorts or voltage shorts

Discussion in 'General Electronics Chat' started by relicmarks, Apr 4, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    Whats the difference between a current short VS a voltage short?
    any examples please?

    HOw do you know when your testing a circuit that it has many shorts? but how would you tell "where" they are at?

    Types of Shorts:
    1.) VCC to ground
    2.) component shorts
    3.) AC signal shorts
    4.) 12 volt short ( when using relays or LED's)
    5.) Any other ones please?

    Some shorts raises the current why is that? why does the current raise up?
    What kind of shorts are these?

    Some shorts will Draw more current from the wall wart , what kind of shorts are theses that draw more current from the wall wart power supply?

    How do you know if its a current short or a voltage short?

    I know audio shorts don't harm or draw alot of current or raise the current up , AC signal Shorts don't draw or raise the current up they just kill the signal off

    What other kinds of shorts are there and to test for please?
     
  2. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    There are only 3 types of shorts:

    1) Short to Vcc
    2) Short to GND
    3) Pin to pin short

    These cover all your short circuit conditions. As to a current short, if you shorted a current source to a potential, then it depends on what the potential is as you may crush the current source.
     
  3. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    A short is a (usually non-intentional and unwanted) conductive path.

    Talk about a 'current' or a 'voltage' short is meaningless.


    Is a short circuited capacitor a short to Vcc or a short to "GND"? Or a short to somewhere/thing else?

    Number 3) is, at best, ambiguous. What do you mean?

    And what is 'crushing' a current source?
    .
    .
     
  4. rwmoekoe

    Active Member

    Mar 1, 2007
    172
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    i beleieve that you can answer the question yourself by digging more understanding in the principles of electricity. you'll then find these questions are hard to answer. (maybe because they are not questions afterall).

    understanding principles, and not just memorizing terms and formulas, is what i will suggest.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Any unintended conduction path is a short. Adding modifiers so as to make one appear different in some way from another does not change the nature of the beast. Short circuits can happen because a component has an internal problem, like a capacitor subjected to overvoltage or a transistor that failed due to overheating. A conductor can drop onto a circuit board and make a path. Bad soldering can short two adjacent pins on an IC together.

    They are all short circuits, they all negatively affect the circuit operation, and they all need to be corrected. Finding a short requires careful observation as much as anything. Looking for a bad capacitor, for instance. You also need to be able to read and understand the schematic so you can trace the signal path and find where it departs from what would be expected.

    This falls under the art of troubleshooting. Some people get good at it, some people take the Mr. Goodwrench approach.
     
  6. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    355
    0
    applying a current limited low voltage and tracing the voltage drop

    What can i use to do current limitting?

    Tracing the voltage drop? how would i know which voltage drop is bad ? can u please explain more?

    Can i use a protection diode to help out also? but a diode between the wall wart power supply and the PCB circuit ?
     
  7. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    355
    0
    how do you guys find SHORTS ? what are some basic steps to take when finding a bunch of SHORTS?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    We drive right off the cliff here. There is no one way to discover a short circuit (when you say "bunch of shorts", I think of J.C. Penny) that works in the same way every time. Short circuits are not that common that don't leave smoking and charred evidence of their location.

    If I have just soldered in a new component and things fail to work, I'm going to take a look at my work to see if there is a solder bridge causing a short circuit.

    Years ago, I worked on a system built around a Lockheed SUE minicomputer. On occasion, the computer did not work, but erratically. Investigation showed there was a triangular feather of solder under the mask that just about came in contact with an adjacent bus line. Up to some frequency of alternation, data passed unaffected. But there was some critical frequency where the solder feather started to act as a short circuit between the traces and messed up the pulse trains. The effect could be seen on an oscilloscope, but had to be found by eye.

    I've had a TTL chip die in a logic plane. The only way to find it, as Vcc was sucked down to about 200 mv, was to cut the 5 volt bus traces until the voltage came up. Then it was simple to bridge the last cut and feel for the hot chip. Can't use an oscilloscope because there are no signals. The temperature probe on a Tektronix 475 would have been very useful, though.

    I invented the smoke test back in 1963 when the family Chevy kept blowing the taillight fuse. I had no wiring diagram to follow, and could not search through the wiring under the dashboard. So I jammed the key in the fuse clips, and pulled it out when all that smoke came out from under the dash. It turned out that the motor that kept the dashboard clock wound had developed a short circuit. I just clipped the wire with the insulation melted off. Got quite a chuckle when I discovered the smoke test in a Navy manual about 6 years later.

    Every technician has a zillion stories, some of them about finding short circuits. They don't all happen alike, nor is it automatically the first thing you look for.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    His name is Walters on all the other electronic chat forums.
    He doesn't seem to understand electronics and got banned from some other chat forums. His millions of questions are frustrating to see all over the web.
     
  10. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    355
    0
    Thanks Audio guru

    I'm not looking for trouble just to talk electronics
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Hi Relic Marks Walters,
    No trouble.
    I see your same questions on many electronics chat sites.
    This site and Google have many tutorials that might help you learn about electronics.
    Some of us learned it in University.
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    If your in need training, visit Davidson College at http://www.phy.davidson.edu/instrumentation/NEETS.htm and download the Navy Electricity and Electronics Training Series [NEETS]. It will give you the technicians view.

    Then when you have questions, they will be a little more structured and you can reference where you were when the question popped up.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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