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Motherboard capacitors question

Discussion in 'General Hardware' started by JunkBear, May 19, 2014.

  1. JunkBear

    JunkBear

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    I have to change capacitors on a mobo that still start and post in bios.

    The rated voltage and farah have to be respected but what about the size of it ? let say a capacitor of 1/4 inch will it be same thing as one of 1/2 inch ?

    Thx
  2. eidairaman1

    eidairaman1

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  3. JunkBear

    JunkBear

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    I know that site but thank you. Anyone else can answer?
  4. stinger608

    stinger608 Dedicated TPU Cruncher & Folder

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    As long as the voltage and farah are correct it shouldn't matter how physically large the cap is. Of course as long as it doesn't interfere with anything else on the motherboard.
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  5. JunkBear

    JunkBear

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    The physical size does not matter and one of them...volt or farah can be changed without problems. Just dont remember which one.
  6. TRWOV

    TRWOV

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    volts can be higher (it indicates how much the cap can bear not how much it needs). Farahs also have a little wiggle room (plus-minus 5% should be fine).

    Capacitors in parallel add their capacitance.

    Size, any will do as long as they have the space.
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  7. AsRock

    AsRock TPU addict

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    I believe it's volts that can be changed although better keep to spec unless the you think a higher volt cap would work better. Check the replacement cap too for lifetime as some are as low as 1000hrs. Samsung are terrible with caps and did some checking on my Sammy 204b and hold and behold 3 bad caps which you replace and shit works again. When i got the LCD it had a 3 month warranty and the caps were rated 3000hrs which failed just after 3 years lol.
  8. Frag Maniac

    Frag Maniac

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    You never mentioned whether each is electrolytic or solid state. Solid state ones are often smaller, but run cooler and last longer.
    Last edited: Jun 7, 2014
  9. shovenose

    shovenose

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    Also keep in mind that you also need to match up the ESR and ripple rating. Usually a bigger capacitor can withstand more ripple.
  10. JunkBear

    JunkBear

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    It to recap à 775mobo and a 478.
  11. Frick

    Frick Fishfaced Nincompoop

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    You have to measure the distance between the pins too (I forget what that is called in english) for proper fitting.
  12. theoneandonlymrk

    theoneandonlymrk

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    Pitch, and some caps are electrolytic ie directional some are not mobo caps normally are directional ie have a defined positive and negative cathode
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  13. lilhasselhoffer

    lilhasselhoffer

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    Wow, somebody has no idea what they are talking about. Go to the asterix if you don't care about why, and only want to know what you can do.

    First, a capacitor can be simply thought of as two plates, separated by a dielectric. The dielectric has two purposes, it prevents the potential from each plate from traveling, and it serves to keep plate distances relatively constant.

    With this simple model, the voltage rating is how much potential can be applied, before the charged plates will discharge through the dielectric. The Farad (what in Hades a Farah is eludes me) rating is how much charge can be developed. For the beginner again, one Farad is one Coulomb with one volt potential difference. The distance the plates are from one another determines how many Farads a capacitor can develop at a given voltage.

    Now, the plate capacitor isn't reality. You've got film capacitors (very close to the plate, but rolled up), ceramic, metallic, and super capacitors. The later two types generally have very specific usage, so you're unlikely to see them. Unfortunately, the first two are insanely common. The next step boils down to capacitance and cost. Ceramic capacitors take a good deal more money to produce, so generally are limited to smaller voltages and capacitances. Film capacitors are easier to make when larger, so find their primary use in through-hole applications and where large capacitance values or voltages are in use.


    *
    Bringing it all back around, make sure to choose the appropriate capacitor type first. You should be able to tell the type visually, as film capacitors will be large canisters while ceramic capacitors are oddly shaped.

    Next, choose a capacitor with the right capacitance values. This value has to be accurate, as too much or two little will fundamentally change how the circuit works.

    Finally, choose the voltage. You ideally want to be as close as possible here (to the original values), but choosing one with a slightly higher voltage rating won't hurt too much. The concern is that if you choose one too much higher the increase in plate spacing of dielectric will force the capacitance lower. Thinking about it as a hyperbole, the ISS and any metal object it orbits over are technically a capacitor. The spacing is so huge that the capacitance value approaches 0, and the potential needed to produce this capacitance is gigantic (think lightning on crack levels of insanely powerful).
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  14. Bucho New Member

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    Back to school I say! Hehe ... no offense.

    To the topics question: size does not really matter here
    Capacitors with the same electrical specifications are manufactured in different dimensions since they sometimes need to be as low as possible because the case is low, or they have to be thin (a small diameter) since a lot of them have to fit next to each other and so on.
    In general it is true that (assumed you always want to replace the same type, lilhasselhoffer named a few) you want the same capacitance, and the same (or if you have to - a little higher) voltage.
    In addition to that you should know that there are some other values you might want to check. There is the temperature range (most common for radial ones up to 85°C and 105°C on electrolyt capacitors but there are way more), the ESR value, the tolerance and many more.
    These may be importand depending on the usage of the capacitor. On a mainboard with lots of ICs and low voltages (<=12V down to ~ 1V) some of these specs are important since any other values may lead to a unstable system.

    So for a mainboard you want to use 105°C since they degrade slower than the 85°C ones at higher temps (that usually appear in a computer). And you want to check for LowESR values, but sometimes it is hard to find out the values of the old ones and the new ones.

    So the best bet is to find exactly the same ones (maybe a different brand since sometimes manufacturers used cheap ones), same capacity, same voltage, same temperature range, same size, same ESR.

    I repaired a lot of mainboards, PSUs, monitors, satellite receivers ... over the past 15 years since I first had a Pentium III mainboard with the problem of bad capacitors. Sometimes it was hard to find the same capacitors (size) but I never had any problems.
    Oh and don't think that "better" capacitors or these with higher voltages always are better, it really depends on the usage. There was a test with a computer PSU once where they exchanged the "cheap" capacitors with quality ones, that also had slightly different values (not voltage, capacitance and the major other values) and the general performance of the PSU got worse! Ripple noise went up. Sometimes circuits use underrated capacitors, that's true but most of the times you can't just simply modify the circuit without exact knowledge of the whole system.
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  15. JunkBear

    JunkBear

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    Found it on eBay. 15 capacitors to repair both motherboards 5$. 105degrees. Unknown brand but Im not sure the 478 still work so i did not to pay extra for nothing
  16. theoneandonlymrk

    theoneandonlymrk

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    Happy days and good luck with it..
    Let us know how you get on.
  17. AsRock

    AsRock TPU addict

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    Cool, sound like 1000h ones.
  18. JunkBear

    JunkBear

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    It will be my first time to repair a motherboard so I prefered to go cheap. :)

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