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Zero Potential is not ground, How do you tell the difference?

Discussion in 'General Electronics Chat' started by Billy Mayo, Dec 12, 2013.

  1. Mike odom

    Mike odom Active Member

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    applying power to the board with a shorted component, the shorted component will HEAT UP... use a thermal (or sometimes a cell camera works) camera to find the hot spot.
     
  2. Billy Mayo

    Billy Mayo Member

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    What type of camera detects heat?
     
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    For the most part, any digital camera can detect infrared (a component of heat).

    Try pointing a digital camera at your TV (or other) remote control device while pressing any button on the remote (aimed at the camera, of course).

    See the little flashes?
     
  4. dave

    Dave New Member

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  5. Billy Mayo

    Billy Mayo Member

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    My manager thinks when u measure two nodes that are in the milliohms its a short, is this true? Or is this a zero potential?
     
  6. ChrisP58

    ChrisP58 Well-Known Member

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    It depends. I can measure two ends of a PCB trace and see a few milliohms, but I don't call it a short because they are intentionally connected.

    The word short implies an unintended connection allowing current to take a short cut, bypassing the circuitry that it is supposed to flow through.

    As for differentiating between a short and 'zero potential' they are two ways of saying the same thing. It's pretty hard to have much voltage across two nodes that are milliohms apart. For example, it'll take 1000 Amps flowing between two nodes 1 milliohm apart to produce 1 volt of potential.
     
  7. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    just a thought but if this bad board is the same one you have done a few posts on over the last week or so, surely its now cheaper to bin the board than it is to continue to fault find. Unless of course it's a $$$$$$$$$ kind of board, but then i think if it was a $$$$$$ kind of board they are being brave letting a novice tech loose on it.
    One other thing i am curious about, you talk alot about your manager telling you stuff but you dont seem to be asking him the questions you ask here??? is there a reason for that? i am not being rude but i dunno something isnt adding up for me it just kind of feels?????????????????? wrong
    I think there is something big you are not talking about or telling, like maybe you got a job by slightly upping it in the interview and now out of your depth and need help??? again no rudeness intended but i get questions in my head when i read your questions. If i had the knowledge to help you andi thought you had lied to get your job and were worried about losing it i would still help, but i dunno something isnt right here to my young simple mind you feel wrong
     
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  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Absolutely not. What you need is a Milli-ohmeter or a tone Milli-ohmeter.
     
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  9. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    LG, I've had the same concerns and since Billy doesn't seem to respond to most posts, except to generate another question, I don't get the feeling he's, I don't know, absorbing the answers. To be sure, he did answer, perfectly, my simple E=IR questions.

    Billy, can I ask what your job is?

    Is it repairing random boards from who knows where, or are they boards from a manufacturing process that have failed some automated test, or what?

    Maybe if we had a little better idea of the direction of your questions (like, where are you going with this), we might be able to better focus our answers.

    I ask this because your questions are all over the place.
     
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  10. JimB

    JimB Super Moderator Most Helpful Member

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    Oscilloscopes, Ext Inputs, phase measurements, time meaurements... etc

    Meters, resistance measurements, transistor tests, capacitor tests, zero potential or ground... etc

    My Manager, testing boards, 115v 400hz 3 phase supply... etc

    These posts by Bill Mayo are all over the place. Guys are being dragged along, trying to be helpful and all the time the topic goes around and around then drifts onto something else.
    I think that Billy is either taking the piss or is totally incompetent and incapable of learning, which is it?
    I suspect the former.
    Walters re-incarnate!:eek:

    JimB
     
  11. Billy Mayo

    Billy Mayo Member

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    True, I agree

    But not all shorts , cause components to get HOT right?

    Are all shorts in the milliohms?

    When an IC chip 7400 family or op amps has a SHORT from VCC to ground, I can't measure Milliohms from the IC pins VCC to ground or if the IC chips has an internal short inside the chip to ground
     
  12. Billy Mayo

    Billy Mayo Member

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    When you have a short, Is taking out IC chip one by one until the short is gone a good approach?

    Isn't there another approach or how to isolate where the short is at?

    Removing IC chips one by one takes hours and days

    This is not a good approach I think
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Let's say you have a board full of 7400 chips and bypass caps. Say one of the bypass caps or IC's are shorted. You can't apply power, because the fuse blows.

    There is always the visual inspection. And say, you COULD apply non-protected power to the board and the circuit board trace would act like a nice fuse. So, that does find the problem.

    So, if you have the board schematic or better yet have the actual PC layout, you can clip a wire to ground and start probing the 5V pins with a milli-ohmeter, As you get "Closer" to the short the resistance will drop. Current likes to follow the path of least resistance.

    See: http://www.nutsvolts.com/index.php?/blog/post/build_an_audible_milliohmmeter/
     
  14. Billy Mayo

    Billy Mayo Member

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    What is an non protected power? an external power supply?

    The +VCC to the IC chips or the + VCC going to the stage?

    Can you use a Milliohm meter from VCC pin to ground pin on a IC chip 7400 family? or Op amp?
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Non-protected means no fuse or an over rated power supply with no or little current limiting, Say the system had a 3 A 5V supply that shut down or blew a fuse and you connected it to a 20 A supply. The circuit now becomes the fuse.

    You would basically be looking for the lowest resistance from the common or ground to an IC VCC pin, assuming that inside an IC the or say a bypass cap is shorted. The technique is not specific to any family. I just used 7400 TTL as an example.

    The chips Vcc to the Chips ground might actually be useful if done 4 terminal (kelvin) connections.
     
  16. Billy Mayo

    Billy Mayo Member

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    Ya I don't think my manager would like this approach

    Why a 4 terminal milliohm meter ? why not a 2 terminal milliohm meter?
     
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Jim,
    I am of the same opinion, this guy already knows the answers to the questions he keeps asking.:banghead:
    His posts are written by someone who is familiar with electronics terminology.

    Each answer he is given gives him the opportunity to ask a further question which he creates from the answer.

    Eric
     
  18. picbits

    picbits Well-Known Member

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    Indeed - I sense either trolling, a 10 year old who doesn't listen or someone who has blagged their way into a job.

    The refusal of Billy Mayo to respond to a direct question is also very similar to another member on here who also posts in a similar fashion. I've seen repeated requests for him to post schematics which never seems to happen.

    I watch you guys going round and round in circles trying to help these people and they keep asking questions until they find the answer they want to hear, not necessarily the answer that is correct.

    All these mentions of his "manager" make me think he's a student and has been given these questions as parts of assignments.

    I'll ask this question directly to "Billy Mayo" - what is your job title, what is your level of education, what is your level of electronics experience and what country are you located in ?
     
  19. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Hi ALL, Billy would you mind answering a couple of questions for me please.
    1) what exactly does this company do?
    2) what do they MAKE or REPAIR?
    3) If your MANAGER is so clued up then why are you doing the trouble shooting and not him?
    4) If your training, then why are they not training you?

    What i really cant understand is if your company makes something or tests something and as it appears from your posts they are many many bad boards (perhaps your a repair shop that make sense), then the bit i really dont get is you have a FLUKE multi meter (££££) and yet the scopes you mention are all old??? i can see someone like Nigel having a old analogue scope on the bench because of its advantages to his work, but you dont seem to have the basic equipment to do the tests that you seem to need to do.
    for example we are simple hobbyist's me and dad and yes we have a very well equipped lab for hobbyist's, but we are way better equipped it seems than a company who's job it is to repair stuff?????

    5) why dosnt your company have a basic 5 1/2 digit bench multi meter??? you can get older ones pretty cheap, you use older scopes so why not say a old dacal multi meter?? that would trace a short no problem and is 4 leads meaning you can have very accurate milliohm readings. Infact our Dacal reads into the uOhm range.

    6) if shorts are a big part of your job then surely they would have a TONEOHM?? you can find a short very very quickly with those and for a business i would say they are cheap.

    Can you answer these please because otherwise i have to say your a :troll: sorry to be rude but i ave outlined above some of the stuff that to me dosn't add up, i dont see how we have the equipment to do your JOB and yet your Company dosnt???


    EDIT
    DAD asked me to post this bit from here.....................................................................

    If your company really was as half arsed as you say it is then it would have gone to the wall a long time ago, a company large enough to employ a trainee and have a manager DOES NOT WORK the way you are saying and stay in business long. Alot of the equipment you seem to need would have been picked up a long time ago. so yes you are a :troll::troll::troll::troll::troll::troll::troll::troll::troll::troll:

    LG though is learning alot from the answer's, just a shame you have chosen to post the way you have


    LG again

    Sorry picbits we seem to have posted at the same time
     
    Last edited: Dec 14, 2013
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  20. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Well, Billy, for my part (as though it matters to you),

    I 'm done with your nonsense...
     
  21. Billy Mayo

    Billy Mayo Member

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    My Fluke Bench Meter has a 20 milliohm button and a 200 milliohm button , it also has a 2 wire or a 4 wire button

    Most Bench meters types has these options, can't these be used for troubleshooting shorts?
     

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