Can anyone read burnt resistor colors?

Discussion in 'Electronics Resources' started by Kyle Hunter, Jan 20, 2011.

  1. Kyle Hunter

    Thread Starter New Member

    Jan 20, 2011
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    I've got a burnt resistor here and today is the first time I've ever even tried decoding a resistor I am just not sure if I have the colors right . .

    [​IMG]
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Have you tried a meter yet? Sometimes they don't change value.

    If the orientation matches the 1/8 watt one visible, then black-black-white-gold makes no sense. Neither does brown-white-black-black.

    I suspect there is a problem that caused the resistor to burn. Be sure you find that.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What does the resistor do in the circuit?

    A rough guess of the value can be made from there, and tweaked later.

    A lot of base/gate resistors in amplifiers turn completely black when the transistor fails, but they are often small value (< 500 ohms).

    Resistors do not burn on their own, it's usually a $5 transistor that will die to protect the $0.05 fuse, which takes out the resistor with it. :D
     
  4. Kyle Hunter

    Thread Starter New Member

    Jan 20, 2011
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    Unfortunately I do not have any idea what the resistor does, it is on a climate control unit for my 97 Suburban and I can not find a schematic. I also have very limited knowledge of electronic circuitry but I have a thirst for knowledge. The switch that controls the blower motor was the first thing to act up. After looking at component prices I decided that it would be more fun to buy a solder station and resistor along with a new switch and still come out money ahead of buying a new control unit . . as long as I can figure out this resistor. Thank-you for all input so far, I certainly appreciate it.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Do you have a digital multimeter (DMM)?

    You'll need one to get it going.

    Pics of both sides of the board that resistor is on will help as well.

    First, try measuring the value of the burnt out resistor, then the task is to find out what other part failed, causing the resistor to burn.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The multiplier band, presumably the band that appears white, is a place to start. Since it is from a car A/C system, I am assuming it at relatively low voltage. If it is a 1/2W resistor, then you can start to put some limits on its values, assuming the resistor was OK before it was exposed to excessive voltage.

    E=IR and W (power) = EI == I^2R. If the power rating was exceed by 100 (i.e. 50W), that would require roughly 4A. At 12V, 4A would imply a 3 ohm resistor. Going thorough various combinations, I would assume the multiplier is not really big, i.e., not 10^4 or greater. In fact, I would assume it is more likely brown, black, or silver, possibly red. Gold appears to have held up, if the tolerance band is any indicator.

    Now, if the multiplier were silver, then the value would be 0.xx. Assume the two black-appearing bands were originally the same color, or one color plus black. You can see where this is going buy now, I hope. Brown,black, silver is 0.1 ohm, That might be used in a current sensing circuit. Are the copper traces fairly large going to the resistor?

    Of course, I am not saying it is 0.1 ohm, 0.22 (R,R,Silver) is another option of many, but I think it is a small value. I am assuming that black and brown paint probably doesn't become white, but silver probably will (silver oxide). If you could dissolve flakes from the band, a good test for silver is the precipitate it forms with halogens, like chloride (i.e., table salt). But then, that is a whole other post.

    If you have a resistor(s) with brown, black, and red bands and can over heat it/them, you might determine which colors change to what.

    John
     
    Last edited: Jan 21, 2011
  7. debe

    Well-Known Member

    Sep 21, 2010
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    What was the climat control not doing? Ones Ive worked on in Fords in Australia control fan speed electronicly & temp is controlled with a servo controled mixer door. This mixes cold & hot air to get the desired temprature. A decent clear picture of both sides of the circuit board may be a help.
     
  8. Kyle Hunter

    Thread Starter New Member

    Jan 20, 2011
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    The blower motor switch broke and I believe is what led up to the resistor burning up. The harness connection to the blower motor switch is also a little on the toasty side.

    [​IMG]

    [​IMG]
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You've got a short in your blower motor!

    Plain and simple.

    Check the blower motor before giving the electronic gods another sacrificial resistor body.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    It appears the failure is off board. Harness or blower motor.

    Check them out with a DMM, and repair the traces on this PCB when replacing the resistor.

    Can you get a bigger pic of the bottom with a bit more light and clear focus?

    Still trying to figure out what else may be wrong. If you could use paint to label the harness connector, and which knobs do what, that'd help a bit as well.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi Kyle, Do you have any resistors to bake to see what color the bands turn into? I was thinking 350 to 400°F (same temp as you use for a frozen pizza) and check periodically. If that doesn't work, I would then turn the broiler on, but still leave the temp the same.

    Please let us know. I am curious.

    John
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
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    Red always seemed to go black first on carbon resistors.
     
  13. Kermit2

    AAC Fanatic!

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    Go to the junk yard.
     
  14. debe

    Well-Known Member

    Sep 21, 2010
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    Looking at the underside of the board the blue conponent has 2x3lots of pins & a seperate 2 pins. I suspect this is a dual ganged var resistor with a switch. The burnt res is on one side of the switch. This board i suspect is only a control board for another module, which may be where the problem is.
     
  15. beenthere

    Retired Moderator

    Apr 20, 2004
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    Has the OP used an ohmmeter on the resistor yet?
     
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