multi-meter with pc board question

Discussion in 'General Electronics Chat' started by dukebdx12, Feb 24, 2008.

  1. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    I have finished soldering this project to a pc board. I soldered my red and black wire and connected the battery to it. I set my multi-meter to DCV 20V and the battery is 9V but when I check it with the multi-meter is says .9 and when I try to record the corresponding value of the BJT collector voltage it says 0.00 for anything I try. What have I done wrong? Will I have to re-do this project?

    And in my first project I went through it fine. Now whenever I try to get the voltage my battery is very hot for awhile. Never did this earlier.
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I think either your battery is dead/weak or your circuit is drawing far too much current and overloading the battery. Without a schematic, we cannot really tell you what you did wrong.

    By attaching an appropriate power source to a circuit, there is no way that's voltage would drop that low under normal circumstances.

    Steve
     
  3. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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  4. hgmjr

    Moderator

    Jan 28, 2005
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    A hot battery is a sure sign that you have a very low resistance across the battery terminals.

    Disconnect the battery and set it aside for now. Set your DVM to ohms and measure the resistance between the connections on your circuit for the battery. If you have a low resistance (just a few ohms) then search for the location of this low resistance.

    hgmjr
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Either the circuit you made is completely backwards or your 9V battery is dead/weak. It would be impossible for this circuit to draw more than 60mA no matter what you did with the potentiometer.

    Steve
     
  6. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    this is not my board but mine looks just like it.
    http://i27.tinypic.com/15hmt15.jpg
    For the resistor wire at the top I am having trouble using it the stretch across the board to put into the port for the positive battery side. The one on the bottom I got fine because it only had to reach to the negative aisle. What can I do to fix it? Can I just solder the resistor to the board clip the remain and try to solder that wire by itself and see if it will reach?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    I have a sneaking suspicion that you have the 10k potentiometer connected incorrectly.

    The wiper arm of the pot is usually the middle terminal, but this isn't always the case - especially if you're using a "trimmer" pot.

    Try measuring the resistance across the pot with it turned to either extreme. If you measure less than about 200 Ohms with the adjustment turned to either extreme, it is not installed correctly.
     
  8. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    nothing will measure. Anything i put the multimeter to it says 0.00. After I try some things out the battery gets so hot i cant even touch it. When I put the multimeter to the battery(the only thing the multimeter will measure) it says 0.04 or 0.09 something like that.
     
  9. hgmjr

    Moderator

    Jan 28, 2005
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    Do you have another battery that you can measure to see what it reads?

    Are you sure that you are not setting the multimeter to measure AC volts?

    hgmjr
     
  10. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    yes. I used both 9V batteries and same thing. Everything on the pc board is 0.00. Yes I have used 20V in the DCV and tried 20K in OHM and both say 0.00 for anything.

    Looks like i will have to make another board. Can I just melt the solder and take the potentiometer and transistor out and re-use do I have to used new ones? I have more transistors but not any more potentiometers.
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    I wonder if your meter leads have been damaged.

    You may want to try to use the meter in ohms setting to test each of your meter leads one at a time. It should read OV or something similar when the meter leads are not shorted together. It should read less than an ohm when the meter leads are shorted.

    hgmjr
     
  12. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    i think i might have it. I will post back here when I'm finished and let you know
     
  13. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    for the picture i gave I am putting the black lead of the multi meter on a negative conductor and put the positive on the base and try to get .50. I got 0.52 and then when I try to connect the red lead to the collector it reads 0.00. This is all in OHM set on 20K. When I try to do this in 20V nothing will read. Everything is 0.00 which I need to be doing this in V. I think I might just have to re-start this project.

    when I put the multi-meter to the battery it reads 0.00 or 0.02 everytime. This is when the meter is on 20V
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    What concerns me is that your voltmeter reads 0.09, when connected to the battery with the battery disconnected from the circuit.

    Isn't that what you said?

    hgmjr
     
  15. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    well I tried to fix the problem. I have now decided to re-do the project because i can not figure it out and I don't see anything wrong so my thinking is I don't see anything I can do differently when I re-do it and it will look the same. I am just hoping it will work. What my problem was is now whenever I put the meters on the battery using V it will read 0.01 and when I try to measure anything else on the pc board it will stay at 0.00. When I try 20K (OHM) the battery reads 0.0 something and when I tried to measure the base and the collector they both read the same at 0.27 which I should be getting the base at around .50 by adjusting the potetiometer and the collector should read something like 9. something. Whenever I try to touch anything else while in OHM it will read 0.00. This is done while I had the black meter on the ground of the pc board and the red meter touching what I need.
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Duke,

    Measure your circuit with the ohm meter set at 2k.

    Across your battery terminals I would expect you to get the same reading as holding the leads apart ... over 2k. If you get anything less than that, look at each solder connection on both the ground and the hot side to ensure you have not bridged across them causing a short.

    Once you read > 2k between the + and - of the battery snap, then you can measure the remaining circuit.

    The hot battery tells you that you've drawn way too much current. And you reading millivolts on the battery tells you that your battery is TU, I mean dead.
     
  17. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    well i got 2 days to do it and I took my transistor and potetiometer out of the currect pc board and going to re-do it. I am going to concentrate on it and make sure I make my soldering very good. And what do you mean by this? What are some examples that are common that I could cause a short and make this all happen?
     
  18. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    i am starting on a new one. If I think the last one happened to have a short in it can I re-use the wires,transistor, and potetioimeter? Or do I have to have everything new on the new pc board?
     
  19. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You can test those components before you install them.

    If your previous attempt failed because of solder bridging across the V+ and V-, your components should be okay.

    You should have troubleshot your problem to gain experience.

    Solder bridges occur when you apply too much solder and it connects two points ... like V+ and V-, or any other two points you didn't want to connect. It can happen anywhere if your not careful.
     
  20. dukebdx12

    Thread Starter Active Member

    Jan 29, 2008
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    i think i might have done the last part by maybe putting to much solder and it connects 2 points....like on my ground. This time I will make sure to be very careful. I will give you an update later today as I will start on this project this afternoon when i get home from school.

    How would I go about testing the components before using them to make sure there not damaged? Just put the multimeter to it?...I'm new to most of these items.
     
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