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What Is The Ohm Of This Resistor

Discussion in 'Troubleshooting and Repair' started by Gregm, Dec 3, 2013.

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  1. Gregm

    Gregm

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    Jun 3, 2010
    I am attempting to repair a fence charger. This resistor as you can see is burnt and is hard to read, but can anyone help me to identify the resistor value?

    Thanks in advance for any help
     

    Attached Files:

  2. duke37

    duke37

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    Jan 9, 2011
    It could be in the 100k range. Hard to see how a high resistance could be burnt unless it has been hit by lightning.

    What is the make and model of the fencer?
     
  3. Gregm

    Gregm

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    Jun 3, 2010
    Thanks for the reply.

    The fence charge is from Southern States and is a Fieldmaster model: 500-1 for 15 miles of fence. Most likely it got hit by lighting as we had lightening one night and it was dead the next morning.

    I have looked at it a number of times and under a magnifying glass and the colors appear to be brown–white-white-red-gold a resistor calculator showed this to be 19.9k ohms 5%
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I don't think you can tell anything from the colour bands of a resistor in that condition.

    Have you tried to find service information for the unit?

    Can you post a photo of the board? If we can figure out what part of the circuit it is in, we might be able to suggest an appropriate value to try.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Unfortunately, after it has been so comprehensively fried, it is hard to rely on the colours as they tend to change.

    Can you show us the board that you took this from? It may give us a clue as to what it was used for and therefore a better information to guess from.

    Alternately, do you have (or do you know anyone else with) a working unit of the same model?
     
  6. Gregm

    Gregm

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    Jun 3, 2010
    Thanks for the reply.

    Before posting, I did a number of internet searches looking for wire diagram, information on resistors and fence charger repair. I do not know anyone with a working unit.

    Please find the photo requested, the resistor came off the left side of the board.
     

    Attached Files:

  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK, that's a start.

    Can you take a higher-resolution photo with the wires moved so they don't obscure things. Also if the large yellow cylindrical capacitor can be detached from the board, move it out of the way as well.

    Can you tell us what those wires connect to. There seem to be four thick wires and two thin wires.

    Can you take a photo of the underside as well.
     
  8. Gregm

    Gregm

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    Jun 3, 2010
    I can take a high res picture, but the site limits the size, so I need to compress it. Do you have a suggestion how to upload the high res picture?
     
  9. duke37

    duke37

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    Jan 9, 2011
    I have looked at several fencers, mostly Gallagher, but not come across a Fieldmaster.

    There are many wires connected to the board

    Red, black, green
    2 black
    2 blue?
    2 yellow
    yellow, green

    What do the wires connect to?
    What is the power supply?
    What is the IC ??324KN ?
    Are the white rectangular components marked?
    What markings are on the big yellow capacitor?

    I see no oscillator to generate the high voltage so perhaps it uses a doubler from the mains.

    There are two commercial repairers of fencers in the UK, one in Wales and one in Scotland, perhaps you have one in Gallifray who could provide a schematic for a consideration.
    Perhaps the maker could help? I have had help from Gallagher but they come from a civilised part of the world !
     
  10. Gregm

    Gregm

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    Jun 3, 2010
    Thanks for the reply. I live in the US. Please see new pictures.

    The red, black, green are connected to a transformer that is connected to AC plug. The 2 black wires go to another transformer (at least that is what I think it is) that connects to the wires that would go to the fence/ground. The 2 blue go to the big yellow capacitor. The 2 yellow (please see picture). The yellow, green go to a light on the front of the charger that pulses as the charger pulses.

    The power supply is a transformer, cannot see any numbers on it. The IC LM324AN / KGA2520 / 9835nN. The white rectangular components, which I think are resistors 5W 1 omega signJ and 5W 0.68 omega signJ. The big yellow capacitor see picture.

    Are the white rectangular components resistors and how do you test them and what should they read?

    Thanks
     

    Attached Files:

  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I can't really tell what's happening with the yellow wires. It looks like it's a loop that goes through a hole in the core of the output transformer... is that right?

    Yes, the white rectangular components are resistors. the 1 omega J is a one ohm resistor and the 0.68 omega J is a 0.68 ohm resistor. Measure them with a multimeter set to its resistance range. They may measure slightly higher than the printed value, because of the resistance of the test leads. Check by touching the leads together. The meter will show the test lead resistance. Subtract that value from the resistances you measure for the resistors.

    There's a diode connected to the resistor that went up in smoke. It's the grey blob with a black stripe. The other end of it goes to the thick black wire from the transformer. It's worth checking that diode. Use a multimeter on diode test range and measure both ways round. One way you should measure around 0.7V and the other way you should measure open circuit.

    You should also check whether the big yellow capacitor has gone short circuit. Measure resistance from end to end.

    To be able to guess at the value of the resistor, we would really need the circuit diagram traced out, I think. I can't tell what that part of the circuit does from those photos. It might be in the charge path for the capacitor, which is why I suggested checking the diode and the capacitor for shorts.

    What are the markings on the big yellow capacitor?
     
  12. Gregm

    Gregm

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    Jun 3, 2010
    Tested the diode got 1 and when I changed the leads got 618.

    The big yellow capacitor P10s43 Type UY1??? The other numbers are not readable, when I moved the strap also has on it ITEM#581-09.
     
  13. tryppyr

    tryppyr

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    Oct 22, 2013
    If you need another of those big 1 ohm resistors let me know... I have a bunch of them (and no use for them).

    Also, you CAN post larger pictures. Generally, the suggestion is to limit the resolution to 800 x 600, but you can go slightly larger and still stay within the image size limits.
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    With JPEG files, the file size is greatly dependent on the amount of compression that's used when the file is created or saved. Heavy compression affects the image quality. Sometimes, higher resolution with heavier compression can yield an image that looks better but is a smaller file. Too much compression causes visible artifacts in areas of high contrast, which is why the JPEG format is not suitable for schematic diagrams and other diagrams.

    You can upload your images to any image hosting site and use IMG and /IMG (with square brackets around them) to mark up the URL so the image appears in the post. (I think that's how you do it; I've never done it that way.)
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    That sounds right.
    That's not enough to tell the value of the capacitor :-(
     
  16. tryppyr

    tryppyr

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    Oct 22, 2013
    Another way is to push the files to a hosting site and use URL and /URL (with brackets around them) to create links to the images (or other types of files). This enables you to post links to really large images/files without making the thread more challenging for those with slower network connections, because someone has to click on the link to incur the download bandwidth consumption.

    I always advise trying to make posts as user friendly as possible. ;)
     
  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes that's a good idea, especially if the pictures are large. There are still people with dial-up Internet access!
     
  18. duke37

    duke37

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    Jan 9, 2011
    The big capacitor has 250V marked on it. Assuming 1J in the pilse, the supply current can be estimated if the capacity is known.

    The blown resistor may be in the input line to get this capacitor charged (to 200V)) in 1 second.

    The LM324 is a quad op amp. A first check would be to see if there is power to this.

    The yellow wire loop through the transformer core could be a low voltage pulse feedback.

    The rectangular resistors may be to limit the current through the SCR.
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I wondered about that, but it's only a small resistor. A resistor in that position would be dissipating quite a bit of power, I think.
    I guess so... but why would it be run through a hole in the core, instead of around the core as a single turn? Seems pretty strange to me!

    Edit: to the OP: There are LOTS of markings on the yellow capacitor. Please post ALL of them.
     
    Last edited: Dec 4, 2013
  20. duke37

    duke37

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    Jan 9, 2011
    The typical energy in the pulse is 1J, within a factor of ten !
    Taking 1J at 1/sec gives 1W so the power required is very low and a surge resistor for the input circuit would dissipate very little power.

    Putting the yellow loop through half the core would presumably give a lower output than a complete turn. It is a pulse transformer and may have several volts/turn.

    A circuit diagram is needed !
     
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