Guide: Replacing capacitors in the EPoX 8RDA+
Motherboards
Written by Gizmo   
Sunday, 12 June 2005 15:27
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Guide: Replacing capacitors in the EPoX 8RDA+
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Motherboards age, and eventually wear out.  In many cases, this provides a good opportunity to upgrade, but the 8RDA+ is a rare exception.  It is, quite simply, one of the most solid products ever made by any company.  It does, however, pose some unique challenges.  Read and discover what it takes to replace the capacitors in this venerable product.

All things wear out with time and use.  Our motherboards are no exception.  Most often, they die because the electrolyte used in modern electrolytic capacitors dries out and causes the capacitor to lose its ability to store charge.  Whatever the reason, when the mobo bites the dust, we generally use it as a an opportunity to upgrade to something newer and better.  Every once in a while, though, a motherboard design comes along that is such a solid performer that it makes it worthwhile to try to find out exactly what is wrong and why.  The EPoX 8RDA+ is one of those motherboards.  However, it poses some unique challenges.

 

The Challenge

 

What, then, is the challenge?  Well, put simply, the challenge is the capacitors themselves.  It would appear that the 8RDA+ is designed to use a particular size of capacitor that is rather difficult to find in the required ratings.  The main problem revolves around the capacitor diameter.  Capacitors from Panasonic, Murata, Rubycon, and virtually every other capacitor manufacturer I could find are larger in diameter than what the 8RDA+ is designed to use.

"But wait!" I hear you say.  "I know people who have replaced their capacitors with parts from those same manufacturers!"  Ah, but did the board work EXACTLY the same as it did before they replaced those parts?  In all the references I have been able to find where people used parts from these manufacturers and found parts that would fit, the board never had quite the level of performance it had previously.  This was generally chalked up to some kind of 'damage' to the board or the CPU when the caps finally blew out. "'NO!" I say!  The problem is because they didn't use the RIGHT capacitors.

 

So, what's the big deal with capacitors?

 

Capacitors are rated according to their ability to store a charge, or their capacity.  This capacity, referred to as capacitance, is measured in Farads.  Since a Farad is a very, very LARGE unit of charge, capacitors like we are dealing with are measured in micro-Farads, denoted as µF.  However, not all capacitors are created equal.  Just because a capacitor has a rating of 1,000 µF doesn't mean that it can replace any other capacitor with an equal rating.  Capacitors are also rated according to their operating voltage (typical voltages are 6.3, 10, 16, 25, 50, 63, 100, all the way up to very high voltages in the range of thousands of volts).  In addition, capacitors have temperature ratings for both heat and cold, tolerance ratings (how much the actual value of the capacitor can vary from its nominal, or ideal value), and ESR and ESL (a measure of how the capacitance will change with frequency).  ALL of these things taken together determine how well, and even if, a capacitor will perform in a given role.  The engineer responsible for the design of a given product will generally try to take all of these factors into account when selecting the capacitor to be used in a product in order to ensure that the proper component for the job is used, while also minimizing cost.

So, what are the rules for replacing capacitors?  Well, in general, you want to try to get one that is as close as possible a match as you can get for the one you are replacing.  You can usually (but not always) substitute a higher capacitance part for a lower one (e.g. use a 1200 µF part instead of a 1000 µF part).  You can usually (but not always) substitute a part with wider temperature tolerances for one with lower temperature tolerances (for example, use a 105C rated part in place of an 85C rated part).  You can substitute a part with tighter tolerances for one with looser tolerances (e.g. a part rated at +/- 20% for one rated at +/- 50%).  You can substitute a LOW ESR rated part for one with a higher ESR rating.  I have never seen an instance where doing either of these was a problem.

So, more is better, right?  Well, not always.  For example, some voltage regulator designs (generally older linear designs) will begin to oscillate if their filter capacitors get too big or too small.  In addition, their ability to respond to input transients may be impared.  Further, you should NEVER substitute a higher voltage part for a lower voltage one (at least, not when substituing electrolytic parts, which is what we are talking about here).  Electrolytic capacitors require a certain minimum operating voltage or their internal structure will begin to break down.

There.  Now I've just imparted a year's worth of learning to you in the space of one page.  LOL.

All of these factors come together to dictate the size and shape of the capacitor.  And therein lies the rub; the 8RDA+ uses capacitors that are narrow and tall, while capacitors available today tend to be more of the short and fat variety.



 

Let's fix my board, already!

 

So, okay, you now know more about capacitors than you ever really wanted to.  How does this help you fix your board?  Simple, silly!  You've got to have the right parts for the job!  Fortunately for you, I've done the necessary research.  The part numbers and where to get them can be found at the end of this article.

In addition to the parts, you are going to need some basic tools, so let's get to it:

 

The tools

 

First off, you need a minimum of a 35W temperature controlled soldering iron.  These two requirements are necessary, or you will most likely be greeted with failure.  The capacitors we are going to be removing are attached to very large power and ground planes on the board (which is a fancy way of saying they are soldered to really big chunks of metal).  Oddly enough, these planes act like huge heat sinks, taking the heat of the soldering iron away from the area that you are trying to heat up enough to melt the solder.  This means you need an iron capable of generating a lot of heat.  However, you need for it to be able to control the temperature of its tip, because it is possible to actually burn up the board if you get it too hot.  You should also use a reasonably large chisel-point tip instead of the more common conical tip.  The chisel-point will allow you to achieve a more efficient heat transfer to the work area.

Here is a picture of the unit that I use:

There are many other units available out there, but expect to pay around $75 or so for even a low end unit.

In addition, you will need a way of removing solding from the existing components.  There are a lot of different ways to do this:  desoldering wick is the cheapest, but can also be a major pain in the posterior to use.  Desoldering wick is basically just copper braid that has been soaked in solder flux.  You use it by simply placing it over the area to be desoldered and heating it with the soldering iron.  When the solder gets hot enough to flow, it 'wicks' into the desoldering braid.  It is very useful in situations where you are dealing with highly shock sensitive circuits, but that is about all (and I generally prefer to use a true desolding station for those).  My personal prefered method is a device known as a 'solder sucker'.  This is basically a spring-loaded vacuum pump, which provides a powerfull sucking action to remove molten solder.  Chose whatever method works best for you and is within your budget.  A true desoldering station is very nice to have, but they can be pricey (more than a good soldering station).


 

You will, of course, also need solder.  Regular 60/40 (60% lead, 40% tin) will work just fine, but I personally prefer to use silver-solder for things like this because it produces a good, strong joint, and once I get this work done I don't want to have to rip the computer back apart again.  There are very good lead-free solders out there as well.

Lastly, but arguably the most critical:  USE A STATIC MAT AND FOLLOW STATIC PROTOCOL!  The last thing you want to do is to go through the trouble of reparing this board, only to discover that you destroyed it through careless exposure to static.

 

A Word About Static

 

I know many people are of the opinion that if you didn't feel the shock, there wasn't a static discharge.  Well guess what folks.  YOU'RE WRONG!  Just because you didn't feel it doesn't mean it didn't happen.  The average human cannot feel a static discharge of less than five thousand volts unless it hits a really sensitive part of the body.  Most components can be damaged by discharges of as low as one thousand volts.

I've also heard statements like "I've worked with electronics for YEARS and never worried about static-free stations or wrist straps.  It never caused ME any problems."  Well, I'll say that it did, but you didn't know it.  A part that is damaged by ESD (electro-static discharge) may not appear to fail right away.  In fact, it may appear to work just fine for a while.  However, it is quite likely that component will suffer a premature failure due to the ESD event that didn't happen because you "didn't feel it".

Static mats and wrist straps can be purchased at any reputable electronics store.  In a pinch, you can make a mat using a piece of cardboard covered with foil and attached by a wire through a one megaohm resistor to a ground (the ground prong in your electrical outlet; just be sure it's grounded.  A water pipe or electrical conduit usually also will work).  A wrist strap can be made using foil wrapped around wrapped around your wrist, and also attached via a wire through a one megaohm resistor to ground.  Even a watch band or bracelet can be used, so long as it is metalic.  In short, don't give excuses for not having a grounded static-free work area.  For the cost of some aluminum foil and your time, you can make one.

 

Are we there, yet?

 

Finally, we get to the actual work.  First, you need the board, and you need to identify the components to be replaced.  Generally, only the parts around the VCore regulator will actualy be 'blown' but as long as we are doing this, we might as well get all the likely culprits.  In this picture, I have circled all of the parts we will be replacing:

View a larger version of the image

The rest of this is pretty straight-forward grunt work.  Pull a part out, find the matching capacitance and voltage among your spares, put it back in and solder it in place.  Be very careful, though!  Most electrolytic capacitors have a polarity.  They will generally be marked with a colored band that runs from the top to the bottom of the cylinder, and that band will have a big '-' symbol printed every so often inside it.  This is the negative voltage side of the capacitor.  If you don't see the band, then the capacitors will also have one lead that is shorter than the other.  This short lead is the negative voltage side of the capacitor.  When you remove the old part from the board, pay special attention to how it is marked and oriented.  It should be marked in the same fashion, and you need to make sure that you put the new part in with the same orientation as the old part.  If you should happen to pull the part out and forget how it goes back, don't despair.  The board will also be marked with a '+' sign on one hole and a '-' sign on the other hole, indicating which orientation the capacitor should be placed in when it is inserted.  Just make sure you get the caps in correctly.  They won't live long if you don't.  :(

 

So, where do I get these magical parts, anyway?

 

That, dear reader, is a very good question, and one that caused me to have to do a CONSIDERABLE amount of research.  In the end, I only found one vendor who had all of the required components.  The caps I found are made by Nippon Industrial Corporation (NIC).  You will need the following parts:


NRSK102M6.3v8x11.5TRF (1000 µF, 6.3v) (need 6)
NRSK152M6.3v8x20TRF  (1500 µF, 6.3v) (need 6)
NRSK222M10v10x23TRF (2200 µF, 10v) (need 4)
NRSK332M6.3v10x23TRF(3300 µf, 6.3v) (need 6)

I was able to aquire mine directly from NIC as engineering samples, and I received ten of each.  However, it is unlikely you will be able to obtain them this way.  You should be able to purchase them through Arrow Electronics, Hamilton-Hallmark Electronics, Future Electronics, Jaco Electronics, Gateway  Electronic Components, or Gothic Components.  You can also go to their web site at http://www.niccomp.com/worldrep_dist.html-ssi to find a distributor near you. When I initially did this, the parts were brand new to the market and only Arrow even had them in their catalog, and they indicated they were a special order item with a minimum order of 200 pieces of each part.  However, things should have changed since then.  Expect to pay something in the area of $20 for the replacement parts and shipping, plus about two hours of your time.

 

If you decide to do this, please leave some feedback in this thread in the forums and let us know how you get on!

Credits 

Many thanks to Daniel ~.  Without the sacrifice of his board under the scalpel, this article would not have happened.  I'll let him speak to the efficacy of the repair.

 
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