Can't identify surface mount device (smd) component - no visable markings

Discussion in 'General Electronics Chat' started by Dion Botha, Jul 17, 2015.

  1. Dion Botha

    Thread Starter New Member

    Jul 17, 2015
    Hi guys,

    I am trying to identify this surface mounted component on 2 failed 4 number LED display boards. I have examined it under a microscope but cannot see any markings/symbols/text, though it is hard as most of the device is submerged in some sort of conformal coating. I can see tiny wires going from each pin inside the component to the center square and inside the center square there is like a kind of mesh (appears conductive). My thoughts is that it is this component that has failed due to the pins being exposed to the environment (as everything else seems to be either coated or looks fine) - observed in both display boards. Does this look familiar to anybody? Maybe some sort of optical sensor/transmitter?


  2. #12


    Nov 30, 2010
    That might be as simple as an LM741 operational amplifier with an unusual coating. (We certainly can't read the lack of markings from here.) If you have a lot of experience in IC fabrication at the wafer level, you might figure out the function by using a microscope, but I doubt you have that skill set. The next level of discovery would be to sketch out the surrounding circuit in hopes of getting a clue about what the chip does. Displays only use a few kinds of functions and 8 pins is within the range of a person to map out the circuit.
  3. ian field

    AAC Fanatic!

    Oct 27, 2012
    It looks like the position array like the ones in CD/DVD laser heads.

    The reflected beam is diverted by a surface coated mirror and projected onto an array of photo-diodes. They indicate positional displacement, focus etc, and read the intensity of the relected beam.

    Some HP/Quantum hard drives had optical head positionsensors, like that - but 80DIL thru-hole parts.

    There's probably something vaguely like that in an optical mouse.
  4. Brevor

    Active Member

    Apr 9, 2011
    It looks like it's mounted on a large led display board, it could be an ambient light sensor to adjust the brightness of the led's.
    Roderick Young likes this.
  5. ian field

    AAC Fanatic!

    Oct 27, 2012
    The favourite for that was the cadmium-sulphide LDR, but AFAIK: they've been banned under RoHS. The LDR was fairly close to the human eye response.

    Silicon photo-diodes peak nearer IR, but I've seen one implemented in a daylight sensor in a light fitting - several earlier models had LDRs.

    Why they'd use an opto-position array for ambient light sensing could probably be explained by; they got an exceptional price deal on those parts and no end of line notice.
    Roderick Young likes this.