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Identifying a component

Discussion in 'General Electronics Discussion' started by KMpuggy, Mar 23, 2011.

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  1. KMpuggy

    KMpuggy

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    Mar 23, 2011
    Hi people, wondering if anyone can help me out as im at a dead end.


    I picked up a 42' samsung plasma telly cheap knowing that it had a dodgy psu, clicking when you turn it on and i was expecting blown capacitors. But nothings never that simple with me. Turns out the caps are fine and one of the the Mosfets have blown, looks like it shorted out, thats not a problem i can source them parts. Its ive noticed that an smd transistor has blown, got a chunk missing out of it. Now that is the problem as i cant source that part. Stamped on it (B3J1) which means nothing when i search for one. How do i source the right part or identify it to get another one?

    They do do a kit for this telly, works out £30, but even if i brought that kit it still might not work as there might be an underlying problem thats caused the problems in the first place., The last resort would be to send the board off and get it repaired. (£60) The 2 Mosfets can be brought for next to nothing, (fqpf9n50c) and its just that smd thats holding me back, so it would work out less than a fiver in total if i can get hold of the parts, and if it dont work, then just a fiver wasted.

    One of these little things, how do i know which one it is as there are so many out there?

    [​IMG]

    Any help would be much appreciated.
     
  2. davenn

    davenn Moderator

    13,492
    1,830
    Sep 5, 2009
    from the circuit board what is the designation screenprinted on the board ?

    eg ... T2 , Q6, D22 it would help to identify if its a transistor or a diode for a start

    the ... B3J1 is that all on 1 line ? as written to the left
    is it a 2 pin, 3 pin, 4 pin device ? your generic example pic shows 2 pins
    how many pins on the other side of the device ?

    maybe you could show a SHARP focused zoomed in pic of that area of the board showing the device and others around it


    cheers
    Dave
     
  3. KMpuggy

    KMpuggy

    6
    0
    Mar 23, 2011
    Thanks for your reply.

    Its a 3 pin one, and the B3 on the chip is wrote length ways along it, and the J1 is wrote across it. Its the same as the one at the top of the pic.

    You can see where i un-soldered it, (Red arrow)

    And you can see where the Mosfet went, damage has been done to the circuit from where it blew. (White arrow)


    [​IMG]

    [​IMG]
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,291
    2,727
    Jan 21, 2010
    It looks like you damaged the board removing whatever that white arrow is pointing to.

    The red one is DX804, sounds like a diode. It looks like the 2 pins on one side are common, or one is not connected, or perhaps there's 2 diodes in there with the other pin having a common anode or cathode.

    The white arrow one was mounted on the other side of the board? Looks like the through-hole component are possibly labelled on the other side.

    You're not the lone ranger. Here seems to be someone who's done a similar fix.

    Nice photos. Can we have some of the other side?
     
  5. KMpuggy

    KMpuggy

    6
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    Mar 23, 2011
    The damage done to the board was from where it blew, not my dodgy soldering. :D And yes i have come across that post you mentioned, the same sort of repair was done (the QX801 and QX801) they are the these HERE

    Its just that other little 3 pin thing that i cant source.

    Picture from the other side of the board. You can notice that the other Mosfet blew after i re-soldered the first mosfet back on. Thats got me thinking is that its an internal short with Mosfet number 1, that caused number 2 to blow, along with that other little transistor/diode thingy underneath the board.

    Or like i said, it could be something else underlying, i wont find out until i replace these parts.

    [​IMG]

    [​IMG]
     
    Last edited: Mar 23, 2011
  6. davenn

    davenn Moderator

    13,492
    1,830
    Sep 5, 2009
    ok so the B3 is the identifier, the J1 is probably manufacturer or date of manufacture

    will consult my SMD bible ;)

    ok B3 = ISS184 dual switching diodes here is a link to the datasheet

    http://www.s-manuals.com/smd-files/pdf/1/1ss184_g.pdf

    its probably not too critical and any similar one could be used in there

    Dave

    PS.... looking very closely at the photo, I would also be highly suspecting the lower of the 2 x 20 Ohm resistors immedialely below the diode you have removed. Look at the black mark right in the "0" of the 20
    it looks like a burn mark. That is the common look for a zapped SMD resistor. Unlike the blobs of solder flux you can see on those 3 other resistors to the right. 2 x 20 ohm resistors in parallel should give you 10 Ohms can you measure across them and see what you get ?
     
    Last edited: Mar 23, 2011
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,291
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    Jan 21, 2010
    OK, looking at the damage to those pads, it appears to me that there is a lot of stress placed on the leads of the mosfets (presumably) which leads to the tracks being torn from the board on the other side. Did the pads come off when you removed the solder?

    This indicates a possible reason for failure and noting what appears to be discolouration around the drain and source holes, but not the gate hole tends to confirm that there was something bad going on there.

    I would measure the resistance across the diode you removed. It is quite likely shorted. This *may* be the reason for the mosfet failure.

    If the diode has the same markings as others on the board, try to determine the polarity of the other diode(s).

    It looks like only a single sided board, so it may be possible to trace where those diodes are connected and from that determine a possible replacement.

    I'm not really enamoured with those links going under the heatsink. Do they look like a recipe for disaster to you? How is the heatsink mounted? Can it move and apply stress to the component leads?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,291
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    Jan 21, 2010
    Unfortunately I also get

    B3 = MMBD717L
    B3 = HSMS2813

    The former has the right code, the latter the right package (the datasheet indicates a different code from my codebook).

    An issue is that both of these have a common anode, and davenn's has a common cathode.

    I wouldn't consider Schottky diodes to be unusual in a circuit like this, however they're both rated for tiny forward currents (not much more than 10mA) so a switching diode would actually be rated for far higher currents.

    Maybe I need a better codebook?
     
  9. KMpuggy

    KMpuggy

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    Mar 23, 2011
    Cheers dave, thats what i was after.

    The kit you can by is this, it replaces the diodes and that around the area, so it might be a better option, but they want £30 for the kit, if i can source the parts myself individually it works out a lot cheaper. But like i said from the start, might pay out for that, replace all the bits, and bang it goes again, £30 down the drain. :(

    [​IMG]

    Steve, im working on it. :D Just dug my multimeter out and its dead, not used in a while and the batteires have ****** up the terminals, so gotta sort that out now then get some measurements. The heatsink is soldered on at each end, it seems quite sturdy and dont move about at all.

    cheers
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    haha Steve well done, dont ya just love trying to ID SMD semi's ;)

    ok maybe when KM gets his multimeter working he may be able to check one of the other diode packages on the board and confirm as to if its common anode or common cathode

    D
     
  11. KMpuggy

    KMpuggy

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    Mar 23, 2011
    They are common cathodes, been ages since ive dug out a multimeter. :D

    And that diode was shorted when i tested it, might explain the bang in the mosfet.

    [​IMG]

    Came across these values for some of the components? But what do they mean and what type of components are they.

    RX804-10K
    DX803-B3

    RX802,RX832 + RX833 ARE ALL 20R
     
    Last edited: Mar 23, 2011
  12. davenn

    davenn Moderator

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    Sep 5, 2009
    10k = 10k Ohms = 10,000 Ohms resistor
    20R = 20 Ohms resistor

    And common cathode agrees with the datashee link I gave you for the diode
    The are all surface mount devices(components) SMD for short.

    dont forget to check that resistor I spoke of a couple of posts ago :)

    Dave
     
  13. KMpuggy

    KMpuggy

    6
    0
    Mar 23, 2011
    Gottcha, i done a year at collage many years ago, got a city and guilds in electronic servicing, but it means crap to me now as ive forgotten it all, and we didnt have micro circuits back then like we have now. :D

    Ive narrowed it all down, and there is a choice between 2 values, flip a coin time i think, dont think there will be much difference between them tho.

    Also ive been reading that the PSUs on these tellys are a major common fault and samsung are replacing most of them free of charge no matter how old it is or out of warrenty. Wish id have found that about them first before i took it all apart. So will replace them bits, if it works then great. If it goes pop again, then on the phone to samsung to tell em to come fix my telly. ;)

    Anyway, cheers for your help.
     
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