Need To Identify Component

Discussion in 'The Projects Forum' started by Big Gus, Oct 17, 2013.

  1. Big Gus

    Thread Starter New Member

    Oct 17, 2013
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    The attached pics are from a Control Board in a Tanning Bed. I have previously repaired this type of board. Normally it is matter of replacing any one of the 18k ohm resistors. Well, on this particular board, none of the resistors tested bad. Below the array of resistors there is a series of LED (which were conspicuously not lit when there was power to the board).
    I measured resistance across the "led" and they all read 11k ohms with the exception of #16 (see pic).
    I am 20 years removed from component level troubleshooting. Reading 11k ohm confused me as I didnt expect that reading.

    There are no identifying marks. I thought I was looking at passive LED now I am not sure. There are no schematics available so I am probing around testing components and trying to signal chase (power).

    Sorry if I am babbling...any help would be appreciated.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Finding one that is different is definitely a clue. What did you observe, open or short?

    Note that a diode - including an LED - will not conduct in either direction until a threshold voltage is met. Testing with an ohm meter is not terribly useful unless you find a short. Most meters have a diode test function but I'm not sure they can be used on LEDs. I'd be tempted to rig up a little power source (e.g. 9V battery plus a 470Ω resistor) to see if I could light up those LEDs.
     
  3. Big Gus

    Thread Starter New Member

    Oct 17, 2013
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    Thanks, I read an open when testing on the ohm setting. I actually just got home and brought a better meter. When testing on the diode setting, the led actually lights up (no external power source in use)
     
  4. #12

    Expert

    Nov 30, 2010
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    That's a perfectly good test result.:)
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Use the same diode test on the optocouplers (white things with 4 legs), one end will have 2 pins that connect to the optocoupler's internal LED.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,093
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    In the first photo, there's a dark spot behind the resistors. Is that a shadow of something on the other side, or is it a sign of overheating?

    Hey RB, what's with the new avatar? Guess I should look into getting one for myself.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Do you like my new look? ;)
     
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