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What are these?

Discussion in 'Power Electronics' started by Pharaday, Sep 11, 2019.

  1. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    20190911_004204.jpg

    What are these? Google doesn't know from the label. They aren't LEDs (or they're blown). Thought maybe photo sensors? Can't detect voltage in the 0-20V range ..... what the heck??
     
  2. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    err.... then I found another one on the main PCB (car sterio) and the board where its attached is labeled "LED1" sooooo.... what the heck... I tried every voltage known to man (starting at 1v, I didn't blow them)...
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Possibly infrared LEDs? try looking atthem with your smartphone camera. These can often detect ir light (shown as a bright spot).
    Make sure to limit the current to approx. 5 ma ... 10 ma when testing.
     
  4. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    ok I'll try that but one of them was found way inside the stereo where I don't think it could recieve anything or get a signal out. But I'll try your thing...

    Edit:
    No, I couldn't notice anything with my phone camera when I hastily tried powering those LEDs from 3v up to about 12... maybe the problem is ME
     
    Last edited: Sep 11, 2019
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Current limited? Did you measure the current? At these voltages any LED will long be gone.
    What does the other side of the PCB look like?

    From the look of it I doubt these are LEDs. No encapsulation - the chips would long have deteriorated. Could these be contacts for pushbuttons?
     
    davenn likes this.
  6. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    20190911_031514.jpg

    It's hard to tell but those 2 metal prongs inside our mystery part are incased in a small rectangle of clear plastic.

    Looking at the PCB, I noticed that there is holes on the back side, possibly for some form of light to get through? Either visible or not.

    Having blown more than my share of LEDs I know what it looks like, a sudden flash of super bright light followed by the LED not working. I'm pretty sure that's not what happened here.

    I won't be able to sleep until we solve this....
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Not necessarily if these are IR LEDs. measuring the current brings clarity.

    Looking real close:
    upload_2019-9-11_12-38-2.png
    1) looks like a bonding wire
    2) looks like an LED chip
    which supports the idea that these are LEDs (this one looks rather similar)
     
  8. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    Well you know what, who knows maybe I blew them. unforch, I bought a multimeter that's just a dual meter; it only measure voltage and resistance, so I guess we could calculate it. I used the same thing I test all LEDs with cause it never burned out any other LEDs. I used a 9v battery plus a 100 ohm resistor. sooo ummmm I=V/R > I=9/100=0.09 amps? Did I... it's been a long time since circuit analysis...
     
  9. Pharaday

    Pharaday

    54
    2
    Jan 18, 2016
    See, this is why I got a B in circuits.... brown black red, that's a 1kΩ resistor, sir. and I measured the battery voltage to be 7.68V so can I change my quiz real quick? I=7.68/1000=0.00768A, couldn't have blown them. Plus you usually see black burns in a blown LED right at the juncture of those 2 prongs, especially in clear ones.... I have blowing LEDs down to a science.
     
  10. Audioguru

    Audioguru

    2,570
    580
    Sep 24, 2016
    If you connect the resistor across the battery like you said without an LED in series then the current is what you calculated. Are you trying to light up the resistor?
    An LED has voltage across it that reduces the voltage across the series resistor so that the current is less than you calculated.

    The battery voltage might be 7.68V when not loaded but if it is old then it could be 4V or less when connected to your LED and resistor. So the actual voltage and current in your circuit might be too low to light the LED.
     
  11. WHONOES

    WHONOES

    662
    134
    May 20, 2017
    Have you tried swapping the battery polarity over?
     
  12. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I'd expect the cathode to sit in the cavity (no. 2 in post #7), anode on the flat part (no. 1).
    But things may be different...
     
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