Does anyone recognize this surface mount component???

Discussion in 'Electronics Resources' started by Pane77, Mar 13, 2015.

  1. Pane77

    Thread Starter New Member

    May 25, 2014
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    Hi there,

    Can anyone tell me what this component might be? It's listed on the PCB as "U", which is INTEGRATED CIRCUIT but the actual marking on the component reads "PMMQ". Seems the "PM" is the same on this component if it's found on another board but the last 2 letters seem to change. It's also in line with the main microprocessor on the board. I've attached a picture and thanks in advance!
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    It is likely to be a transistor in a SOT23 package. The reference designator is U5 which normally indicates an IC (integrated circuit). AFAIK there are very few, if any, 3 terminal integrated circuits. Integrated circuits would be in a SOT23-5 package with 5 pins. The part obviously took a hit and I figure you have zero chance of affecting a repair by speculating on a replacement part without some information on the original design.

    There are some cross reference tables which might help you cross PMMQ to an actual part.
    I've looked at several and can't find a match.
     
    Last edited: Mar 13, 2015
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    One of the common non-transistor, 3-terminal devices is a voltage regulator. However, from the little portion of the pcb that you show, that does not seem like a likely possibility.

    John
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    True enough except don't voltage regulators usually come in a SOT223 with a wide tab?
    Like this:
    http://www.ti.com/lit/ds/symlink/lm340-n.pdf

    The proximity of X1, which looks like a ceramic resonator, suggests that a microprocessor might be nearby.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    You can check with DMM if it is a diode or investigate the traces
     
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    It's a highly toasted transistor
     
  7. takao21203

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    Apr 28, 2012
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    Also it has been reworked / the part was exchanged.
     
  8. Papabravo

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    So even if the toasted component was replaced there is little to no guarantee that a similar fate would not befall the replacement. My vote -- the board is toast.
     
  9. Pane77

    Thread Starter New Member

    May 25, 2014
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    Thank you, thank you, thank you very much for the reply. It seems to be proprietary but I do appreciate all the help I can get. So even though it does not have a "Q" for transistor on the board, you're saying that it just might be a transistor? That helps. I will look into that. Thank you!
     
  10. Pane77

    Thread Starter New Member

    May 25, 2014
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    The component is fine, it was probably a soldering gun that hurt it. The component, if figured out, would lead to the repair of many boards that have this component go bad. The board sells for $700 to $1200 used. It's imperative that we find out what it is. Thanks...
     
  11. Pane77

    Thread Starter New Member

    May 25, 2014
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    How would I do that? I sometimes check transistors in diode mode anyway so how would that help? The trace that stems from that IC goes into the main microprocessor. Thanks!
     
  12. Pane77

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    May 25, 2014
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    That's correct, the microprocessor has the 3rd leg trace connecting to it.
     
  13. Papabravo

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    Incidentally the reason for my belief is that an IC would normally have a Vcc pin and a GND pin. That leaves only one pin for I/O on a three pin device. For those conditions I cannot imagine a useful device. A voltage regulator in such a small package is possible but unlikely. It would have a big tab for a heat sink like the datasheet for the 340 series

    In addition to a transistor it might be a dual diode with a common cathode or common anode.
     
  14. Brevor

    Active Member

    Apr 9, 2011
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    It may be a "brownout detector" IC for the microcontroller.
     
  15. Papabravo

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    An excellent point. I stopped using them after the micros started incorporating that circuitry. Especially if one of the three pins goes to the processor RESET line.
     
  16. Pane77

    Thread Starter New Member

    May 25, 2014
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    I can also add that, without it on there, nothing, the entire appliance, does not work. Also, with it on the board, the ASA signature analysis is as follows in the picture. Basically, diode, diode. Which is normal for any IC so that doesn't help us much but here is a picture anyway.
     
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  17. Brevor

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    Apr 9, 2011
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    I think the proper name is something like "reset controller" or something similar. See what pin on the microcontroller the unknown IC connects to and what it's function is.
     
  18. alfacliff

    Well-Known Member

    Dec 13, 2013
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    if it is testing like two diodes, it just might be a transistor.
    or two diodes, there are smt packs that size with two diodes.
     
    Last edited: Mar 16, 2015
  19. GopherT

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  20. Pane77

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    May 25, 2014
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