5 band resistors

Discussion in 'General Electronics Chat' started by LordsWorkr, Jan 31, 2012.

  1. LordsWorkr

    Thread Starter New Member

    Jan 31, 2012
    3
    0
    I am new to the group so I am sorry if this question has come up before. I have been trouble shooting a circuit board for an electric fence charger and I came across three resistors that don't seem to make sense based on the color codes. (pictures at https://picasaweb.google.com/103468671691828723635/Resistors) When I ohm them out on the board their values don't match the codes. They are all 5 band resistors and R3 may be fusible. Here are the colors (as best that I can tell). R3 measures 13.0K: Brown, Red, Black, White, Blue. R4 measures 13.0K: Brown, Red, White, Green, Violet. R4 measures 79.5K: Brown, Red, Violet, Grey, Violet. I have tried the variations of Orange for Red, Silver for Grey, Violet for Brown to see if anything makes sense but the fourth band multipliers always puts the values in the mega-ohm range. If anyone could explain what I am missing I would appreciate it for future reference. (By the way, the problem appears to be a bad IC which I have replaced resulting in a working system.)
     
    • R3.jpg
      R3.jpg
      File size:
      275.2 KB
      Views:
      68
    • R4.jpg
      R4.jpg
      File size:
      255.8 KB
      Views:
      59
    • R5.jpg
      R5.jpg
      File size:
      282.8 KB
      Views:
      65
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    You can't simply measure resistors inside the board, you need to disconnect at least on lead to get any sensible measurement.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Then measuring resistors in circuit. You will measure the total resistance of the resistor, and what ever that may be connected in parallel with the resistor in question. If you do not have a schematic the best thing is to desolder one leg, and lift it up from PCB. So you are sure your only measure on the resistor in question. Your resistor do not look damaged in any way. So you should be able to measure the correct resistance
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    A five band resistor is typically a 1% tolerance resistor. But, in a 1% resistor, the first three bands are the numbers and the fourth band is the factor of ten multipler. The fifth band is something else like reliability index or some wierd thing you can ignore.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You may be reading them backwards:

    Read it: Violet, Grey, Violet, Red = 787 X 10E2 = 78.7K

    Brown is the reliability index or whatever that last band is (?)

    http://www.hobby-hour.com/electronics/resistorcalculator.php

    BTW: What looks like white may have been yellow.


    Here are standard resistor sizes:

    http://www.rfcafe.com/references/electrical/resistor-values.htm
     
    Last edited: Feb 1, 2012
  6. LordsWorkr

    Thread Starter New Member

    Jan 31, 2012
    3
    0
    So measuring them out of the circuit makes much more sense. Sorry to have wasted time without doing so before. But since the circuit is working again ... I was being lazy.

    HOWEVER --- R4 is still not making sense. The new measurements are:
    R3 70.3K, (Blue, White, Brown, Red, Brown = 69.1K 1%)
    R4 15.95K, (Violet, Green, Grey, Red, Brown = 75.8K 1%)
    R5 79.5K. (Violet, Grey, Violet, Red, Brown = 78.7K 1%)

    I can understand measuring 70.3K for 69.1 and 79.5 for 78.7. But R4 ??? If my ohmmeter connection was bad it should have read high not low. Is it possible for a resistor to go bad and reduce in ohms? (From 75.8K to 16K)
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    You sure it´s violet? Even on the photo it seems like brown, green, grey, red, brown = 15.8K
     
  9. LordsWorkr

    Thread Starter New Member

    Jan 31, 2012
    3
    0
    Yeah, now that makes sense! Guess my eyes are worse than I thought. :-(
    Thanks a lot.
     
Loading...