can anyone identify the fried transistor?

Discussion in 'General Electronics Chat' started by strantor, Aug 26, 2011.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    My friend brought me this remote control. He said the LED doesn't work. Looks like he's gone in with a soldering iron fried the crap out of the transistor that switches the LED. why he was in there with a soldering iron?; don't know. is/was the transistor the only problem?; don't know. what I do know is that this transistor needs to be replaced. If there ever was a part# on it, it's been burned off. I think it matches the dimensions of a to-23 package pretty well. I am pretty sure from looking at the circuit that it's a NPN, the top is the collector, right is emitter, and left is base. can anyone give me a part# for something that has a good chance of working? here's a pic:
    [​IMG]

    Thanks a bunch
     
  2. SgtWookie

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    Jul 17, 2007
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    Probably an SMT version of a 2N3904, like an MMBT3904.
    http://www.fairchildsemi.com/ds/2N/2N3904.pdf

    Several years ago I was visiting my folks up north; their cordless phone had died. Found there was a dead NPN transistor that turned out to be an MMBT3904. No way to just walk in somewhere and buy one of those, but there was a Radio Shack store in town; I picked up a 15-pack of their NPN resistor assortment. They generally come with five 2N22222's, five 2N4401's, and five 2N3904's. A bit of creative lead-bending and soldering, and the phone was back in working order.

    At least, until my dear Dad dropped the phone in his soup bowl... ;)
     
  3. R!f@@

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    Hey dummy..:D.show me a clear pic and I can tell for sure..
     
  4. strantor

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    lol. thanks wookie. I'll see
    hey that's the best I can do with a crappy camera phone with no focus. I tried for 5 minutes to get one that even looks that good.
     
  5. bertus

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  6. strantor

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    Cool idea bertus. It worked, but upon looking at my image I see that the transistor in question (Q1) has fallen off somewhere between my desk and the printer. It was only holding on by half a trace. I have no idea where it is, so even though it won't be of any help, here is the picture for proof of concept:
    [​IMG]
     
  7. debe

    Well-Known Member

    Sep 21, 2010
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    Just a sugestion, we have 2nd hand stores here that have bins of old remotes for 50c-$1 ea get one & ime sure youl find a simmilar transistor in one to remove. These parts are simmilar in most remotes.
     
  8. Sparky49

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    Jul 16, 2011
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    It also looks like the top track (and pad) has come away...
     
  9. R!f@@

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    what kinda junk have u got ? Kid.
     
  10. bertus

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    Hello,

    I have changed the brightness of the picture and selected the bottom part.

    [​IMG]

    It is a pitty that the defective transistor already is removed and can not be seen for markings.

    Bertus
     
  11. strantor

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    That's a good Idea. I'll tell my friend. I already sent him the link for the replacement so we'll see what he brings me.

    It has. He heated it up so much that all 3 pads lifted and the trace all the way to R2 lifted.
    it's remote control junk. I told him to just get a universal remote but he says he already tried that and it won't work. this is for his cheap chinese security camera DVR system.
    Thanks. that looks a lot better. The picture probably still wouldn't be much help if the transistor was there; there were no markings on it, even through a high power magnifying glass. I only posted the first pic for a size reference so that maybe someone could confirm my suspicions as to the package type.
     
  12. R!f@@

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    By junk I meant, tht do u have any PCB's tht you can salvage parts from.
    Basically u can get the tr from TV Pcb's.

    At least I do u know
     
  13. strantor

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    Ah, yeah. Actually I need to check my junk heap at home. I bet I do have that.
     
  14. THE_RB

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    Feb 11, 2008
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    They usually run up to 1amp peak currents, you need a SOT-23 tranny with 1A peak capability, I would just use a BC817 that should get you up and running.

    PS. The LED is likely burnt out too!
     
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