SMD replacement of capacitor, unknown value

Discussion in 'Computer Hardware, Devices and Accessories' started by Scorpei, Sep 17, 2012.

Sep 17, 2012
  1. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Just wondering if anyone would be able to help. I'm working on an inverter board and want to replace what I think is a capacitor. Thing is, I can't really find out what it is exactly. Markings on it:
    (no clear polarity)

    H683
    2N47

    Markings on the board which it is on are C{number}, and seeing as it is near an inductor on an inverter I can safely assume it is a capacitor. However not a clue which one. I thought it would be H = 50V (or 3% margin) with 68 * 10^3 pF, but when I replaced them with a 0,47uF 100V (electrolyte) capacitor the board doesn't function. As I didn't know the polarity (the markings on the original are not clear) I swapped them round and still got no result. I'm baffled at what these things are and perhaps they didn't even need replacing.

    If I can't replace them (the backlight of the unit has failed) I will probably attempt a LED backlight myself as I don't really feel the urge to now fix this inverter (backlight operated sometimes, but then always flickered and died soon after. Could be the inverter was dead, now it is if I replaced the part wrong, or the tubes).

    Any help would be appreciated, perhaps Originality or FAST know this :)?
     
  2. Foxi4

    Reporter Foxi4 On the hunt...

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    Markings aside, you could provide us with a photograph of the part itself, preferably in Macro mode.
     
  3. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Made two with my phone, afraid I don't have any proper camera around right now.
    Pic 1
    Pic 2


    And the inverter board (not mine obviously):
    [​IMG]
     
  4. raulpica

    Supervisor raulpica With your drill, thrust to the sky!

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    Try with 0.068uF at 50V (maybe 500V?). I remember inverters worked on 500V...
     
  5. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Well... I don't have any of those or any ones close. The smalles I have are the .47uF and I can't find any smaller... Would be really surprised if they were THAT low a value though.... anyone have anything definitive on what those things are?
     
  6. wiismodrome

    Member wiismodrome flubber

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    http://www.muzique.com/schem/caps.htm

    683 = 68 nF = 0.068 μF

    Any idea of the voltage in that part of the circuit?  From the physical size, it looks like the voltage rating may be greater than 100 V.  The capacitor pictured is not electrolytic or tantalum, so polarity is not a concern.
     
  7. raulpica

    Supervisor raulpica With your drill, thrust to the sky!

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    Glad to see I was right :P

    Anyway, as we might all know, having a bigger voltage isn't an issue (having a lower one is), so I say Scorpei should go for a 500V one just to be safe! :P
     
  8. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Afraid not..... Was hoping to get a rating off off the old caps... Seeing as they are near the end of the inverter board higher is quite possible. Best I can find that matches (with high voltage) are ceramic caps with 500V rating, but they are only 10nF meaning I would need 7x12 = 84 caps. Not that expensive (about 6 euro's) but will be annoying to get on there :P.

    Seeing as it is an inverter, could it be that these are capacitors for alternating current (Vac)?

    ==quick edit==
    Found some 68nF 630V not too expensive caps.. More then willing to buy them but those would be MKP so current direction specific? [quick edit 2] Source states they are bi-polar....
     
  9. wiismodrome

    Member wiismodrome flubber

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    With film capacitors there is generally no concern about polarity.  One of the links I just read suggested that polarity might make an audible difference when used for audio signals.  For a digital or power supply circuit there is probably no significant difference.
     
  10. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Ordered the caps I linked to (the 500V ones that match the probably capacity). I'll put them on there and if it fixes it probably leave it at that. If not.... LED here I come ;). Naturally going to keep this thread updated.
     
  11. Scorpei
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    Member Scorpei GBAtemp Maniac

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    Replaced the capacitors, sadly, no backlight (as if there was no inverter?). I think I am either still not replacing the caps right, or the CCFLs are really broken. Either way I think I'll be building me a LED backlight soon. Only thing I have to do is measure the power output to the inverter board which probably won't be 12V which means I need to get a supply from somewhere and a relais.
     
  12. wiismodrome

    Member wiismodrome flubber

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    Last time I repaired an LCD backlight the problem was a few bad electrolytic capacitors in the power supply, which is a common failure point.  Film caps don't usually fail.  
    One of these comes in handy for testing: http://www.dealextre...00pf-20mf-27256
     

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