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Capacitors - Mysterious Creatures

How to Fix Your Motherboard for $15
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Capacitors and resistors are the components most frequently used in electric and electronic circuits. Capacitors are used for duplexers, oscillator circuits, as interference suppressors or in the form of electrolytic capacitors filtering of various kinds. Electrolytic capacitors differ from normal capacitors because they use a liquid, an "electrolyte", within their aluminum bodies, conducting electricity when a voltage is applied.

Almost all electronic circuits in power supplies use filter capacitors. These deal with electrical peaks transformers or transistors are unable to handle quickly enough. Broadly speaking, a capacitor doesn't work much different than a rechargeable battery. It will recharge when DC voltage is applied. The capacitor's charge is stored when the voltage source and the capacitor are disconnected. Filtering capacitors equalize voltages, in power adapters, for example.

Transformers will down-transform a power adapter's voltage to the desired level. Rectifiers generate DC voltage from the applied AC voltage. The freshly generated DC voltage is not "smooth", rather it pulsates. The brief voltage drop caused by this pulsation is covered by a capacitor, which functions like an additional voltage source providing a stabilizing amount of voltage. Capacitors with lower Equivalent Series Resistance (ESR) are used to make sure that the stabilization works properly and capacitors are able to cover pulsing without being damaged themselves.

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  • 1 Hide
    Darkness Master , September 21, 2008 8:24 AM
    Recognizing of broken capacitors is not so simple in some cases.
    Sometimes (very often in my case) have capacitor its nominal capacity but it has high serial current. When you connect DC voltage of capacitor nominal value and capacitor have some serial current throught it, then it is broken. Only charging current is allowed (short current peak on connect).
    Sorry for my english.
  • 1 Hide
    4655434b20594f55 , October 27, 2008 7:06 PM
    Good article. I have personally made this repair sucessfully many times using only a basic hand held solding iron and hand held desolder pump.
    Like you say the motherboard sinks away the heat fast. You need an iron with between 70 and 100 watts and a large flat tip. If it spans both solder points of the cap its really easy :) 

    Just heat and gently pull the cap out from the other side of the board. Then clear the holes with the heated pin method or use a desolder pump. If you heat the hole on one side and use the pump on the other side it should clear easily.
    Only other thing to note is. Be QUICK, practice on some junk board first, you dont want to burn a big hole in your board or lift of the tracks.

    Im sure most people don't have a professional solder/desolder station. These cost at least $160 usually more.
  • 1 Hide
    4655434b20594f55 , October 27, 2008 7:11 PM
    Another trick. Assuming the old caps are dead and of no further use. Pull them off thier leads.
    If you pull a electrolytic capacitor hard the leads will pull straight out of the body of the cap.
    Leaving just the leads sticking up. Its now much easier to remove becuase you can desolder the leads and remove them one at a time.
  • 1 Hide
    Anonymous , July 7, 2011 6:00 PM
    Just trim the leads sticking out of the bottom of the board then heat one at a time while applying slight pressure to the capacitor towards the other lead. They pop right out. I use thecapking for capacitors online, fast free shipping.
  • 1 Hide
    Anonymous , July 13, 2011 5:15 PM
    I use the Weller WLC100. It's consumer DIY soldering station, but more than meets the needs for motherboard soldering. Runs about $50. I've done 50+ boards easily with this station, but I use a precision tip instead of the big tip it comes with (usually run about $10). I also recommend Mouser or Digikey for capacitors, though beginners may find these sites overwhelming. TheCapking is a good place to find capacitor kits for common motherboards with faulty capacitors, and the site has diagrams in case you get confused where the capacitors need to go.
  • 0 Hide
    sahil_81 , April 23, 2012 4:46 AM
    ooowowwwwww nice i am verry happy he he he he....... i liked
  • 0 Hide
    runf , January 28, 2013 2:59 AM
    I Turned on a computer that had been working. A short "pop", a fairly intense burning odor, and later I found a capacitor (I presume) on the bottom of my computer case:
    Here is a pic of the Asus P5-K. The green arrow points to where the capacitor used to sit.
    http://jazzdrummer.com/capacitor2.jpg
    First of all I'd like to know if it is indeed a capacitor and if not, what it is. Whatever it is, can I get another, solder it in and have any hope of fixing this board? I'm really clueless, if you can't tell. Any help would be greatly appreciated. This could be an opportunity for me to learn something.
  • 0 Hide
    gabs110 , May 6, 2013 11:56 PM
    I have a MSI mobo which I repaired some months back...replaced 2 caps. Lately, the same symptoms re-occured..pc starts up, fans run, lights light up but nothing else..no sound, no bios, no display. I replaced the same caps again thinking it might be malfunctioning but still nothing and no signs of any other failure. Any advice? My pc is a Acer Veriton M464 duo core.
  • 0 Hide
    Greg Hopkins , May 15, 2013 2:36 PM
    Once you pull a mother board for any bad caps, you should replace them all. The caps are cheap compared to the down time and frustration. Some caps can fail with no obvious signs from the outside. My advise would be to change all the old caps with new low ESR Caps.