Identifying a SMD

Discussion in 'General Electronics Chat' started by urraco, Feb 29, 2008.

  1. urraco

    Thread Starter New Member

    Feb 29, 2008
    2
    0
    It's about my Pinnacle USB PCTVTunner - doesn't work anymore. I've opened it and i figured out that SMD SOT23 package was broken. It's says on it : A018. It's linked directly to +5V of USB.There's another SMD on PCB exactly like it, i've made some measurements(you find them in the MMC.jpg) :i guess it's a zener diode, i don't know for sure. If you have a suggestion, please tell me. Thanks!

    MMC.JPG
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The device is likely to be a transistor with one junction open. The .7 volt reading is typical for a forward biased pn junction. If the other device is identical, it may show two junctions - BE and BC. Use the diode check function.

    Zener diodes break down at a set voltage when reverse biased. To check one, you need a current limiting resistor and a variable voltage supply to find the breakdown (zener) point.
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    If it is on the USB power line, it may be a zener overvoltage/ESD protection diode.

    Such a component is not critical to circuit operation, and it should still work upon removing the possibly shorted component. However, USB power should measure +5V.

    If you remove the failed device and the circuit doesn't operate properly, then you will probably require a schematic to understand the operation and repair it accordingly.
     
  4. urraco

    Thread Starter New Member

    Feb 29, 2008
    2
    0
    A transistor ? No for sure. I know how to measure a component the problem is I don't have the tools (DIRECT CURENT SUPPLY) - a multimeter is not enough, only at work but I can't bring it there(security problem).I've posted this thread hoping that someone know the marking code for this kind of SMD.
     
  5. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    This is most likely a date code and will not tell you anything about the component, except for when it was manufactured.
     
  6. peranders

    Well-Known Member

    May 21, 2007
    87
    0
    I'm afraid not. It's likely that this is the actual marking. BC860C for instance has 4Gp but for this you have to check the datasheet.
     
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