Which Octocoupler?

Discussion in 'General Electronics Chat' started by Xad, Dec 25, 2013.

  1. Xad

    Thread Starter New Member

    Dec 25, 2013
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    I'm looking to get a replacement for this:

    [​IMG]
    I've found Optocouplers here but not sure which one to get: CPC Link How do i know which to get? They seem so similar.





    Below is what the damaged one looks like. Any idea what causes this? If i replace it is it likely to burn out again because the problem is possibly something else? (it's from a faulty Blu-Ray player/PVR)
    [​IMG]
     
    Last edited: Dec 25, 2013
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It's an optocoupler, not octocoupler. Googling 817B plus optocoupler turns up some possibilities; both Avago and Fairchild have optocouplers that could be it. You would need to check the specifications for them and compare those to the DVD player's circuit. Without a schematic, there is some guesswork involved.

    Good luck.
     
  3. Xad

    Thread Starter New Member

    Dec 25, 2013
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    Oops, not sure why i said Octo considering i linked to Optocouplers, lol. The CPC link in my original post, could i just buy a few different ones from that link and test them? Or could that be dangerous (more so than simply burning out?). The only difference between the items seems to be "Continuous Collector Current Ic Max" and "Current Transfer Ratio Min/Max".

    It's from the power supply section of the unit if that helps. It looks like this (Optocoupler on the middle/bottom):

    [​IMG]
     
  4. tubeguy

    Well-Known Member

    Nov 3, 2012
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    When a component blows its top like this it's possible something else is shorted which caused this failure. Best to get a a schematic.
    My guess is the output side on the right is gone.
    If no schematic is available then follow the PCB traces to find possible culprits.
     
  5. Xad

    Thread Starter New Member

    Dec 25, 2013
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    No schematics unfortunately. Found another component that is blown:

    [​IMG][​IMG]


    Also the green capacitor (2a104j) seems slightly bulged at the top, could that also indicate a fault or is that normal?

    [​IMG]







    Here's the full underside of the board (Click thumbnail):

    [​IMG]
     
  6. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Capacitors frequently fail shorted..

    How old is this unit ?
     
  7. #12

    Expert

    Nov 30, 2010
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    My thoughts exactly: "Oh $%^&, it's a switching supply and the isolator blew it's top. That's not easy to do. You have to find where that much excess energy came from!
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The bulge on the top of the green cap is epoxy, they are dipped then dried upside down so many get an epoxy lump on top. It's normal.

    Re the two dead parts, normally to blow them apart like that takes a lot of energy caused by a big arc etc. Neither part has the characteristic black char burns etc that happen during this.

    To me it looks like both parts have been mechanically attacked, ie have been smashed with physical force.
     
    Last edited: Dec 25, 2013
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The SamYoung cap to the left of the green one looks to have a slightly bulging top. That's a bad sign.
    I'd disagree with RB about mechanical attack. IMO both parts have fried.
     
  10. sheldons

    Active Member

    Oct 26, 2011
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    ok the other item that has failed is the TIL431 ....which is used with your opto to provide regulation of your power supply....these components when they fail do cause extra damage to the secondary and primary side of your power supply-i have repaired quite a few of these units ,dont forget to replace the capacitors with high temp types....give me the exact model number of your unit and ill have a look for the relevant service manual
     
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  11. Xad

    Thread Starter New Member

    Dec 25, 2013
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    Model is: LG HR929. On the Power supply board it says HR920 though, guessing that's the all encompassing model number for the various models in the same range (with different hard drive sizes).
     
  12. sheldons

    Active Member

    Oct 26, 2011
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    power supply type depends on the model of the lg to which it is fitted due to type-wether it has a hdd fitted etc,am looking now for the manual
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
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    From the pictures it looks like a fairly typical blowout. If the power chip has a source current sensing resistor - that's almost certainly blown open, the chip GND pin can also lose its bond wire inside the package.

    That type of chip can and does forget to regulate, resulting in core saturation and massive punch-through. Also the chip's VCC is usually supplied by an AUX winding on the transformer - the electrolytic on that rail is also a common cause of regulation failure.

    If there's a source resistor, you have to figure out all the paths the fault current went when that blew open - there will be a trail of damage!

    There's nothing particularly special about the opto, aside from its small size and isolation spec for PSU use - the datasheet is out there on the web, I vaguely remember it being from NEC or possibly Panasonic. Sharp and Toshiba also do suitable replacements.

    The number is 817 - if I could remember the prefix I could have found the datasheet in seconds and posted the link. You could try searching "817 opto coupler".
     
  14. sheldons

    Active Member

    Oct 26, 2011
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    here is your power supply schematic from the manual i have......i do have the full service manual but cant upload it due to size limitations of the uploads allowed here......
     
    Last edited: Dec 27, 2013
  15. Xad

    Thread Starter New Member

    Dec 25, 2013
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    [​IMG]


    I labelled some of the components and labelled some that give no readings.

    1) Is the yellow coin-like one labelled PZ called a piezo resistor or varistor, or both? Is that supposed to give a reading? I get nothing. Also, it has 14K681 on the component but i can only find 14D681K. The specs seem the same (colour blue instead of yellow), would that be ok? Does it even need to be replaced?

    2) The C1 & C2 capacitors i'm going to replace, the green large one on the far left i've already replaced along with the opto.

    3) The blue capacitors on the top labelled C3 don't give any readings, do they need to be replaced also? Or is that normal?

    4) The zener diode labelled Z gives no readings and the resistor labelled R gives odd inaccurate readings, i replace those also?

    5) Finally, right under the PZ component, the yellow cube component, i think it's called a safety capacitor? It has some black soot on it and doesn't give a reading (same with the other one below the blue cap, top right), does that mean it might be dead? Or are they not supposed to give a reading?


    [​IMG]
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    A "peizo resistor" is a new one on me - MOVs (or varistors) often look just like resin dipped ceramic disk capacitors, they should read open circuit just like a capacitor as they only pass a small leakage current until the rated voltage is exceeded. One of the most common symbols on the top screen-print is a sort of "Z" with a line through the middle.
     
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