Toshiba Satellite A300 Motherboard problem

Discussion in 'General Electronics Chat' started by stereotype100, Sep 8, 2013.

  1. stereotype100

    Thread Starter New Member

    Sep 8, 2013
    4
    0
    Hello!

    This is my first post here after having read lots of useful information on the site.
    I have a complicated problem with my TOSHIBA A300 laptop.
    It won't power up, neither with AC adapter nor with battery. No leds on, no signs of life.

    Technicians at a local repair-center told me that there may be a short circuit in the Hall Sensor circuit, because an SMD component (PT3661-BB) is missing. (I indicate it with a red arrow on the photo below)

    http://i1311.photobucket.com/albums/s663/stereotype232323/20130907_024245_zps01df0659.jpg

    I also found out that an A6 diode (BAS316) has also been unmounted from the exact same circuit! ( I indicate it with a yellow arrow below)

    http://i1311.photobucket.com/albums...e-58a7-4d53-8e18-e61a7b420acc_zpsd1d13d3b.jpg

    And this is another photo of the circuit: http://i1311.photobucket.com/albums/s663/stereotype232323/20130907_024308_zpsaf7db66b.jpg

    Now, I am using a multimeter to test continuity and resistance in the circuit according to the board Schematics I found and things seem to be ok. Sadly, I have no AC adapter at the moment.

    I have also tested other circuitry on the board and all seems good,too.
    Truth is, I don't know if that's a safe way to detect a short on the mobo..

    What should I do now? Can these components be replaced for the machine to work again? I don't believe there is a short circuit, because motherboard gave signal to external monitor before I give it to the repair-center.
    There are also no signs of leaked capacitors or bad smell.

    Please guide me as to what I should check. If you need any other information (such as the circuitry diagramms) or more photos, just ask me.

    Thank you in advance for your time
     
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Something is screaming " awfully fishy " here... :eek:
    If SMD component (PT3661-BB) is 'missing' -- where in heck did it go... inside the unit ? ...

    At any rate, the pad indicated by the red arrow, adjacent to " hole 29 " housed a transistor - 3 pad package - possibly a hall sensor... and the pad tagged PC 72 -- yellow arrow & ? -- appears to have never been occupied, since the solder is unmolested >
    Diode 33 - second pict. is definitely gone... or was never there either...

    The "technician" said things were missing... I would think they had to be in the casing somewhere

    I agree, you probably shouldn't be looking around w/ a meter yet.
    Will you post a shot of the schematic you have ?
     
    Last edited: Sep 9, 2013
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  3. stereotype100

    Thread Starter New Member

    Sep 8, 2013
    4
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    Thanks for the answer!
    I think you're absolutely right. Diode 33 is definitely missing, as well as the transistor you mentioned above. I figured it out from the board schematic.

    Here it is a picture of the hall sensor circuit as you asked:
    [​IMG]

    Could these components have ''exploded'' due to a short on the circuit...?
     
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    No, I don't think they exploded, since there is no charring on any board that would indicate an electrical short,,, There has to be some trace of the missing parts in that casing somewhere
     
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  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    That's if they were ever there.

    Most commercial boards have many variations with only partial population to satisfy any given app.

    I assume the laptop once worked?

    If so there should be some sign of life if power is getting through from the supply, even if the board is not properly functional.
     
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  6. stereotype100

    Thread Starter New Member

    Sep 8, 2013
    4
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    Thanks a lot for your answers again!

    According to another used board of the same exact model I found on Aliexpress, these components should be there. If you zoom enough, you can distinguish them (indicated by yellow arrows)

    [​IMG]

    In addition, at the anode ( I think it's called that way) point of the diode, there is almost no solder. It seems like it has been scratched and copper comes into view.

    So, I can assume that they once existed there...

    Sadly, there is no trace of them in the casing...Probably they were lost at the local repair-center...

    I wish you're right..Yes, my laptop worked without problems for over 4 years.
    So, should I find a combatible AC adapter and see what happens?

    I suspect that these guys at the repair center did something wrong...
     
  7. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Hmmmm... now why would that surprise me :D
     
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  8. stereotype100

    Thread Starter New Member

    Sep 8, 2013
    4
    0
    Any other thoughts guys?
     
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