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First time working with caps, is it ok to use bigger cap on lcd monitor?

Discussion in 'Troubleshooting and Repair' started by rastoma, Aug 3, 2013.

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  1. rastoma

    rastoma

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    Aug 3, 2013
    I've never replaced a capacitor on anything before.

    I was given a non-working HP 17" LCD monitor a couple of days ago. It was manufactured in 2005. I plugged it in just to see what it what it would do and it powered up and showed a crisp clear image (hooked to a PC). But the screen went black after about 5 seconds or so. The power light remained solid green.

    After reading an article online about how relatively easy some LCD repairs are, I took it apart and found 3 very slightly bulging caps, all 3 were identical, 680uf 25w. The only source of electronics I have within an almost hour drive of me is Radio Shack. The closest cap they had was 1000uf 33w.

    I replaced them, hooked up the monitor and it's working. I left it on about 10 minutes and the monitor has a beautiful picture.

    Is it OK to leave those 3 caps in it or should I get the exact caps that was in it and replace them again? (will have to order online)

    Also, these 1000uf caps were a little bigger and one of them I could not flush mount against the board. If it's OK to leave the caps in, is it acceptable to have a cap not flush to the board?

    Thank you to whoever took the time to read this and offer any suggestions.
     
  2. techiesteve

    techiesteve

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    Jul 27, 2013
    I guess by 25w you mean 25V, W usually indicates Watts which aren't relevant here.

    One common problem with replacing electrolytic capacitors in modern equipment using high density placement is finding one that will fit. If the capacitors you fitted are secure, not dangling loose on long leads, they will be fine. In this case a slightly higher voltage and capacitance is OK, plus electrolytics usually have a wide capacitance tolerance.
     
  3. rastoma

    rastoma

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    Aug 3, 2013
    Yes.. I meant 24v :)

    I was going from memory early this morning when I posted plus with no experience with values of caps to begin with, I was little confused.

    The one that I mentioned wasn't flush against the board is just raised up on one side about 2-3mm I'm guessing. The diameter was a little larger than the original and the original was actually touching another cap next to it (one that didn't get replaced) so it was a tight fit to begin with.

    So it should be safe to continue to use then I take it from your reply.

    Thanks for the speedy reply and help.
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    something that techiesteve didnt mention is ....

    its important to note the temperature rating on the capacitors
    if they are 85C replace them with 85C or 105C. if they are 105C dont use a lower temp rating

    Dave
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Another two things techiesteve didn't mention are ESR (equivalent or effective series resistance) and ripple current rating. In power supply applications these are often important, and "standard" electrolytics like those sold by Radio Shack may not be suitable.

    If your replacement capacitors have an ESR that's too high, or a ripple current specification that's too low, they may heat up more than they should, and go the same way as the original ones.

    If you still have the old capacitors, post a photo here, or write up ALL the markings you can find. This should include:
    Manufacturer name
    Capacitor series (usually a two-letter or three-letter acronym)
    Capacitance (uF) specification and voltage (V) rating
    Temperature rating.

    From this, we should be able to find the data sheet for the original component and find those parameters, so we can suggest suitable replacements from a US-based mail-order company like Digikey or Mouser.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Another thing is that the caps which fail are almost always low ESR caps. Your replacements may not be. Whilst their ESR may be low enough to start off with, the higher ESR (and possibly lower ripple current rating) combined with their lower temperature rating may lead to early failure.

    As things are at the moment, they are fine to leave in the circuit, just beware that they don't fail soon. If they do, spend some money on good low ESR caps that you won't have to replace again for maybe another 5 years.

    And another thing... Refresh the page before you reply! :D
     
  7. techiesteve

    techiesteve

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    Jul 27, 2013
    I missed mentioning fitting 105 deg C and low ESR caps for long term reliability. I was being hassled by my other half to 'get of the computer and come out'.

    Manufacturers will often cut costs by using the lowest spec they can get away with in consumer equipment, and if being cynical, some believe to build in early obsolescence as they fail.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Wow, that's never happened to me ;)
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    I solved that prob long ago, got her her own puter ;)

    D
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Low ESR electrolytics are not only - or even primarily - used for reasons of long term reliability. They are used to achieve specified ripple levels on the power supply outputs. Using a standard ESR component where a low-ESR component is required can cause problems with downstream circuitry because of excessive AC on the supply rail.
     
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