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SMD components question.

Discussion in 'General Electronics Discussion' started by HellasTechn, Jan 17, 2017.

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  1. HellasTechn

    HellasTechn

    1,532
    212
    Apr 14, 2013
    Good day everyone !

    Lately i had many problems with smd devices, my main issue is to identify them so i can measure them. To be more specific, all PCB's use theese SOT-23 smd devices. I have come across a large number of markings on them and honestly i find it very hard to identify them. Today i was repairing a really cheap 18650 battery charger (had nothing better to do) and i see this SOT-23 marked Y1, so i Googled Y1 sot-32 and find this page : http://www.s-manuals.com/smd/y1 that says sot-32 Y1 is a zener diode. BUT here on this site http://www.hz-dz.net/UploadFiles/20095279518624.pdf i see a sot-32 Y1 transistor.

    So what is going on with theese smd devices ? how can we positively identify them since there is nothing on them to even suggest the manufacturer ?
     
  2. shrtrnd

    shrtrnd

    3,749
    482
    Jan 15, 2010
    You've just discovered this problem?
    People whine about this all the time here.
    Some of the guys here are really good guessers, but a lot of these devices are complete unknowns without the manufacturer being known.
     
    davenn likes this.
  3. freesky

    freesky

    1
    0
    Jan 23, 2017
    sot-23 is one of the packages for components. many components have the sot-23 package .
     
  4. HellasTechn

    HellasTechn

    1,532
    212
    Apr 14, 2013
    Yes.
    The problem is that it can be anything. there are no stantard marking. For example a TO-92 2n2222 is a transistor no matter who the manufacturer is while a SOT-32 Y1 could be a diode or a transistor or a regulator.

    Got the point ?
     
  5. davenn

    davenn Moderator

    13,617
    1,881
    Sep 5, 2009
    that's where it helps if the PCB is screen printed with part numbers ... at least then the part type is known, just its specifics isnt
     
  6. HellasTechn

    HellasTechn

    1,532
    212
    Apr 14, 2013
    most PCB's iv'e seen only state the id e.g. U1 or R112 and if you dont have the service manual or the PCB schematic...
     
  7. davenn

    davenn Moderator

    13,617
    1,881
    Sep 5, 2009
    and that's the HUGE hint as to what it is, as I said before ;)

    U = IC, IC = IC

    Q, TR, transistors

    ZD = zener diode

    D = Diode

    etc etc
     
  8. HellasTechn

    HellasTechn

    1,532
    212
    Apr 14, 2013
    I see your point now. You are right.
    Still a Q could be a bjt, mosfet, thyristor and more. It is better than nothing though.
     
    davenn likes this.
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    The manufacturer knows...

    There are some "codebooks" which list packages, codes, and known devices using those codes.

    Often it's pretty simple. If the options are a zener diode or a transistor, differentiating them is reasonably easy. It's more of a problem when the list of possibilities includes a number of transistors which differ in hard-to-measure specifications (like breakdown voltages)

    Often you have to trace the circuit and determine what component seems reasonable.

    Obviously it's easier if the component still works, but then you wouldn't be replacing it.

    It's a reasonable bet that multiple devices on a board with the same marking are probably the same component, so you may have a method of identifying an unknown component by using its working brethren.
     
    HellasTechn likes this.
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