Which capacitors generally need replacing?

[gintama]

I'm about to re-cap several boards (first time), and I have a few questions that the FAQ hasn't answered. There's basically no info in there about which caps (on a board's layout, not the brand names) usually go bad - I know from reading that the ones around the AGP slot and power regulation cluster are problem areas, but some extra insight on this would be very helpful. Looking at the premade replacement kits for sale on this site, the biggest one contains 30 capacitors, whereas the boards I'm fixing have 52 in total. This is made more confusing by the custom kit order page, which only has places to select three different types.

This motherboard model (Foxconn/Leadtek WinFast K7NCR18) uses 100% GSC's, and the boards are brand new out of the box (retailer never sold them). The two I tested immediately had some venting, and the third has a cap with visibly opened vents and corrosion setting in around the top... Didn't test that one.
I do have an ESR meter, which I had the pleasure of building last year for this project. But I'm not sure where to begin.

So, how does one decide which to replace? On a quick pass over the VRM caps, most were fully open or fully closed. My guess is that everything above the 470uF's need to go - but what about all the small ones? If there's no bulging, what are reasonable values for them? This board has the following:

NUM Volt Value Size (mm width X mm height)
 2x 16v 2200uF 10x25 
15x 6.3v 1500uF 10x20
15x 6.3v 1000uF 8x11
 2x 16v 470uF 8x11
 2x 16v 220uF 6x11
 5x 16v 100uF 6x11
 4x 25v 22uF  5x11
 6x 25v 10uF  4x11
 1x 16v 22uF  4x6

I'll probably use Rubycons, so does this set (following the order of the above list) make sense?

2x PX Series 10x25
15x ZL Series 10x20
15x MBZ Series 8x11

One last question, if I was getting SamXons instead, how would I decide between sizes when there's no exact match? For example the second set of caps (6.3v 1500uF) are originally sized 10x20. The SamXons available are the GD Series (8x20) and the GC Series (10x16). Would I be basing that choice on the usage of the cap (different ESR or heat resistance) since both of them would fit? How about the third set (6.3v 1000uF 8x11), where the only like-rated caps are 8x14? If that's too tall, would switching to a slightly lower uF rating (GD Series 6.3v 820uF 8x12), as has been done in some of the ready-made kits, be acceptable? Thanks.

[PCBONEZ]

Re: Which capacitors generally need replacing?

With GSC I would replace all but in any event at least these:
2x 16v 2200uF 10x25
15x 6.3v 1500uF 10x20
15x 6.3v 1000uF 8x11
2x 16v 470uF 8x11
2x 16v 220uF 6x11

These should be replaced with something comparable to MBZ grade:
2x 16v 2200uF 10x25
15x 6.3v 1500uF 10x20
[I am assuming these are those in the CPU VRM.]

ZL grade would be okay for these:
15x 6.3v 1000uF 8x11
2x 16v 470uF 8x11
[These are assumed to be the scattered filter caps about the board and near the slots.]

The low UF higher volts caps are used more to keep RF Noise (EMI) form entering the board from outside connections (sound, USB, printer, ect) than they are for PSU ripple.
They are much less critical and general purpose low ESR caps are okay there.
Replacement is optional but I would with GSC.

Diameter doesn't matter much as long as it fits and the ESR is in range.
[In the same series of caps larger diameter has lower ESR and higher ripple. - Better.]
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Be aware that (almost always) 10mm caps have the leads spaced at 5mm and 8mm cap leads are spaced at 3.5mm. - That can create more work getting the leads to fit the holes. Leads need to be bent carefully to prevent causing leaks through the seal.

-

I've recently seen some complaints about SamXon failures (right here in the forums) so I'm continuing my "wait and see" on those.
https://www.badcaps.net/forum/showth...ghlight=samxon
See kc8adu's posts near the end.

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[gintama]

Re: Which capacitors generally need replacing?

Good info, thanks. About the replacement caps, I'm guessing I'd need to find another source if I want MBZs for the ones you mentioned - I was looking forward to just grabbing them from this site's operator since the work isn't for me and sourcing small amounts of parts can be tiresome. But it doesn't look like he has MBZ in those values, I'd have to change the uF rating or voltage. For the smaller of the two (1500uF 6.3v) I could move to 16v to keep the same size, from what I understand that would be acceptable. But for the two large 2200uF 15v caps, there's nothing listed with that high of a voltage in MBZ with that much capacitance. Is PX Series not ok? I'll try to find the table of rubycon attributes again, but feel free to link me.

[PCBONEZ]

Re: Which capacitors generally need replacing?

PX is barely a low ESR cap.
Probably not suitable for CPU power except maybe on a P1 or a pre-pentium board.

Here's grades (based on ESR and ripple) from my personal chart.
Brand codes:
NI=Nichicon
CC=Chemicon
RB=Rubycon
SY=Sanyo
PA=Panasonic/Matsushita
NC=NIC Componnts
SM=Samxon

Listed as Brand[dash]Series.
Caps in each line are directly comparable.
Lines go Best Bestest first and Lesser Bestest next. (IOW: Best on top.)

NI-HZ, SM-GA

RB-MCZ, CC-KZJ, SM-GC

RB-MBZ, PA=FJ, PA=FL, NC-NRSJ, NC-NRSK, SM=GD, SY=WG,
and CC-KZG but high failure rates in hot spots (heat problem).

~~
Definitely use those above on low volts side of CPU VRM
- Preferably on high volts side too but next range is usually okay there.
~~

RB-ZLG, SM-GE, PA-FM, NI-HV, RB-ZLH, NC-NRSH, CC-KZM, CC-KZH

RB-ZL, NI-HD, CC-KZE, SY-WX, NC-NRSG, SM-GK

RB-ZT (High temp cap - Not common)

~~~
Next set okay for scattered caps about the board, not prefered in VRMs since about PC100 RAM was used. (For lack of a better time-line.) Some P3 or AMD boards with lots and lots of caps may have used them. (Multiple caps in parallel lowers ESR.)
~~~

NI-PA, NI-HE, CC-KY, RB-YXG, RB-YXH, PA-FK,

PA-FC, NC-NRSX, NC-NRSZ, NI-PW, CC-LXZ, NI-PM

~~~
RB-PX is lower than the last group on my chart. I don't even list it because it's just barely better than a General Purpose cap.

www.digikey.com has loads of CC-KZE, CC-KY, NI-HE sizes available.
KZE would probably do for your 2200uF-16v

The 1000uF-6.3v [If not in VRM] -> KZE, HE, KY are all okay.

eBay occasionally has small/medium sized lots available of various caps.

Samxon are certainly okay for a year or maybe two/three.
I have no proof but I suspect they are using Chinese sourced Aluminum which causes problems due to impurities but that takes some time to happen. Heat speeds it up so with a good PSU and cooling they'll probably last a few years.

.

[PCBONEZ]

Re: Which capacitors generally need replacing?

To previous question.
Yes, going up in volts is okay.
Note on that. - Long term use at a lower voltage will turn the cap into a lower voltage cap because the thickness of the oxide layer will 'adjust' to the thickness for the lower voltage. (But it does not the other way. Going up in volts will damage the layer vice make it thicker.)

Going up in uF (within limits) is also okay. Some sensible people say up to +50% and uninformed moronic overclockers will double it or more but I limit it to one range (standard value) over the 'stock' cap. That usually works out to 20% to 30%. (UF has a 20% tolerance in the first place and uF goes down with age so as it gets older it will get closer to the original value anyway.) If in a bind I might consider 50%.
[One range as in: 1000->1200,, 1500->1800,, 1800->2200,, 2200->2700,, da da dada,,,,]

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[gintama]

Leadtek / Foxconn WinFast K7NCR18D rev.F capacitor map

Thanks again for the posts, I've had a busy week and haven't been able to drop in. Regarding what you said about going with higher capacitance values, that's good to know. Unfortunately it seems I'll have to find another source for those caps anyway, as the 3300uF (+50%) MBZ caps available here are only 6.3v.

I've made up a map for this motherboard, and am linking it for anyone else who happens to want it. Yes, the colour scheme is awful - I couldn't think of anything else that would work in low resolution and still be useful for colorblind people. The polarities aren't marked at all, but that's something everyone should be checking for themselves anyway. If you have time, would you mind pointing out (or maybe providing a link to such info) which areas are what? I know I don't know much about motherboard layout. And although I'm fairly certain where the VRM is, I would imagine a lot of people are in the same boat when it comes to things like "the low voltage side of the CPU" that you'd mentioned previously.


Unaltered photo (297KB):


Capacitor map (224KB):

[PCBONEZ]

Re: Which capacitors generally need replacing?

Just taking a quick look.

The row of 6.3-1500 are CPU VRM output.
- Use MBZ or better grades.

The 16-2200 are CPU VRM input.
- MBZ or better grades because you only have two.
(Some boards have 4,5 caps there and can get by with ZL or similar.)

The 220uF and below all seem to be for I/O RF (EMI noise) considerations. That's higher frequency (RF = Radio Frequency) noise usually comming into the board from external wiring. (USB, Video cable, printer, modem, LAN, PS/2, sound/speakers.) Fan connections sometimes have one or two of those nearby too. (For the motor noise.) They are also sometimes used as signal coupling caps (vice filtering caps) but most boards use SMD caps for that job now. -The lesser grades of low ESR like PA-FC (from above) or even those PX you mentioned would probably be fine there. [Replacing those at all is generally considered optional.] I would use at least PA-FC if it has anything to do with a sound or LAN chip.

The 1000uF and 1500uF not in the VRM should be fine with ZL grade or better but MBZ grade in those sizes are better and fairly easy to get (and not so different in $$$) so you might consider those.

The 470uF should be ZL or better.
They seem to be there for the memory slots which often have localized VRM's of their own but you have lots of 1000 and 1500 in that area helping them out. Same as above. Upgrading to to MBZ won't kill your wallet there either.

I don't see any 3300uF so why is that a concern?

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[gintama]

Re: Which capacitors generally need replacing?

Good walkthrough, thanks! The 3300uF's were mentioned because of what you said earlier about replacing with different capacitances up to ~%50 higher being feasible. 2200uF (the ones I would need to look for) + %50 = 3300uF, which are available here in MBZ series... but only in 6.3V, so it still wouldn't work.

[PCBONEZ]

Re: Which capacitors generally need replacing?

2700uF also exists in low ESR some series'.
It looks like you may have room where the 2200's are to use 12.5mm which should be easier to source in 16v. - Just make sure you don't ground any nearby SMD parts with the outer edge of the caps when you install them.

[chipper]

Re: Which capacitors generally need replacing?

I would replace any cap that has a white or brown residue on them or bulging. As far as uF rating goes , you should be safe if you replace everything including the 470uF caps. The length , and even the circumference of a cap is not an issue , as long as you have the same uF ratings and voltages. I have replaced many caps small and large without any issues about sizes (thin , tall , bigger , smaller) , in fact I am beginning to find that larger circumference caps are better , due to the inside wrappings quality and durabilities in bigger caps.

This is also why I say that 470uF's are big enough and yet small enough to be causing a problem somehow. The smallest caps are practically not wrapped with any kind of substancial "inners" , so they practically don't wear , blow , or change at all.

Using low esr caps is a good idea because caps actually produce electronic "noise" in the circuits while conducting and resisting voltages , esr ensures a smooth flow without creating static or interference type irregularities.

[chipper]

Re: Which capacitors generally need replacing?

The 470uF caps , if replaced with +50% caps = 705uF @(80% = 846uF) , making those caps nearly (1000uF) , what is normally replaced when recapping.

[PCBONEZ]

Re: Which capacitors generally need replacing?

Low ESR caps are typically available in the sequence 220, 330, 470, 560, 680, 820, 1000.
470 is one of the easiest sizes to find.