Need help identifying a transistor

Discussion in 'General Electronics Chat' started by Otaku, Nov 13, 2009.

  1. Otaku

    Thread Starter Active Member

    Nov 19, 2008
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    Hi all,
    I need to replace a blown transistor, but have no idea what to get to replace it. It's a three-pin SMT transistor with the characters "Y 1" printed on the top of the case. I've done a lot of Googling for this part, but "Y 1" is a pretty ambiguous search term, so I haven't had much luck. The circuit board that it lives on is a small battery-powered novelty device that plays back some canned phrases when triggered by a built-in PIR. As far as what this transistor appears to control in the circuit, after it failed the speaker on the device stopped working. The rest of the board's functionality seems to be OK, but no sound. The board is powered by three AA batteries. All help is appreciated!

    Gary
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    This is a very handy resource for finding out such things:
    http://www.educypedia.be/electronics/datacomponent.htm

    From a link on that page, I found this site:
    http://info.electronicwerkstatt.de/bereiche/bauteile/smd/smd_aktiv/y.html
    Code Y1 looks like an 11V Zener diode. It could be 0.3W or 1W.
    If it is a SOT23 package, it is a BZX84-C11. The SOT23 package has two pins on one side, and one pin on the other.
    Link to SOT23 package measurements: http://info.electronicwerkstatt.de/bereiche/bauteile/smd/smd_aktiv/images/sot/sot23.gif
    If it is a SOT89 package, it is a BZV49C11. The SOT89 package has three pins on one side, and a wide tab on the other.
    There is a datasheet available on this page for a BZV49C11: http://www.datasheetcatalog.com/datasheets_pdf/B/Z/V/4/BZV49C11.shtml
     
  3. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    Thanks, SgtWookie. Not sure about it being a diode, though. The board that it's on is printed with Q1 for that part, which typically designates a transistor, I believe. It does have the 3-pin configuration of the SOT23 package. I'll check the links you provided - thanks again!
     
  4. BMorse

    Senior Member

    Sep 26, 2009
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    Can you tell if the collector is connected to VCC or VSS (should be the single pin on one side) and is the transistor directly connected to the speaker??

    The transistor could be part of a transistor amplifier for the speaker output of the device.....

    My .02
     
  5. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    The single pin connects directly to the speaker negative wire. One of the other pins is connected to a trace that goes to the ROM chip where the canned phrases are stored. There is a SMT resistor in parallel across the two pins on the opposite side of the single pin, labeled "189". The remaining pin connects via a trace to the negative leg of an electrolytic cap. The resistor is between the two pins of the transistor and cap and ROM chip, respectively.
     
  6. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
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  7. SgtWookie

    Expert

    Jul 17, 2007
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  8. Otaku

    Thread Starter Active Member

    Nov 19, 2008
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    Thanks, SgtWookie. Could you explain the heat dissipation issue a bit?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    When you're using a transistor as an electrically controlled variable resistor for audio, a good bit of heat can be generated by the power used in the transistor. Power in Watts = voltage x current in Amperes. You need a way to get rid of that heat, or the transistor will overheat and melt.
     
  10. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    Understood. I assume that since the SMT is mounted essentially in contact with the PCB, the board acts as a heat sink? Would using a TO-220 package (don't know if this device is available in that package) and a heat sink be a solution?
     
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