Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

[SwedishDiesel]

Howdy folks,

I have an Optiplex GX260 that blew a couple of those troublesome Nichicon HM series (ultra low ESR) electrolytic capacitors. Because said caps are obsolete, they are pretty much impossible to find on the market; I did find a listing for some but I believe they are counterfeit. I feel the easiest thing to do would be to replace all the blown caps with polymer ones. I am by no means an expert in electronics, and I've found a fair bit of conflicting information, so any guidance or confirmation would be greatly appreciated. While from a practical standpoint it's not worth recapping such an old PC because not much can be done with it, but I like old computers and I'd like to get this one up and running. I want to install quality caps that are suitable for this application; there are some alternatives but they're not ideal for motherboards. As far as I am aware, there isn't a direct replacement for these caps.

A total of 11 caps rated at 2200uf and 6.3 volts (10mm x 20mm) , and 4 caps rated at 1800uf and 6.3 volts (8mm x 20mm) need to be replaced. Two caps totally blew out (and funnily enough the computer still ran fine) and the rest are looking a bit puffy and need replacing.

Firstly, what exactly do I need to take into account aside from capacitance, voltage, size and lead spacing? I’ve found ratings for ripple current, leakage current, tangent of loss angle, and dissipation factor. From what I’ve read and understood, ripple current and leakage are important to take into account, but I have not been able to find an exact match.

Second is the half-capacitance rule - for Voltage Regulator Modules/VRMs, it seems that you should use poly caps with half the capacitance? I've also heard that the capacitance should be kept the same. The same case with non-VRM caps; I've heard you should use poly caps with half the capacitance but I've also heard that capacitance should be the same.

I found some really nice-looking German poly caps with a low ESR rating (12mOhms @ 100khz vs what I believe is 13 mOhms (listed as impedance rather than ESR)) meant for VGA cards and power supplies, but I am unsure if they'd be suitable for this application. They're rated at 6.3v and 2000uf, but they have a high ripple current compared to the OEM Nichicon caps (5900 vs 2550 mArms), and the leakage current (as far as I can tell) is way higher than that of the OEM caps, at 1260uA. There are also 1000uf caps which have a leakage current of 630uA, which is an improvement (assuming the low capacitance isn't an issue) but still much higher. Would the high leakage and high ripple current pose any issues? Assuming I should use caps with the same capacitance, would the 200uf difference be significant enough to cause issues?

2000uf caps specs:                https://www.we-online.com/catalog/datasheet/870025175013.pdf
1000uf caps specs:                https://www.we-online.com/catalog/datasheet/870025175010.pdf
Original Nichicon caps specs:  https://www.nichicon.co.jp/english/products/pdf/e-hm.pdf


Other references:
https://badcaps.net/forum/showthread.php?t=95944        (Capacitance and ESR for replacement VRM caps; mentions sticking as close as possible to original specs)
https://www.badcaps.net/forum/showthread.php?t=7944  (Replacements for Nichicon HM, note that as far as I could find these caps are not available)
https://badcaps.net/forum/showthread.php?t=12932        (Polymod discussion, discusses halving uf rating for VRM caps and half-capacitance rule)
https://www.vogons.org/viewtopic.php?f=46&t=62330      (mentions halving capacitance while keeping same ESR rating and at least OEM ripple rating)
https://www.vogons.org/viewtopic.php?f=46&t=68709      (mixed information on specs of capacitors to use)
https://www.eevblog.com/forum/beginners/can-be-simple-electrolytic-capacitor-replaced-by-polymer-capacitor/         (use the same ratings)
https://www.overclock.net/threads/changing-from-electrolytic-capacitors-to-solid-polymer-capacitors.1333093/          (use the same ratings)

Any feedback or suggestions would be greatly appreciated. If I’ve made any mistakes in here or if I've overlooked/missed anything important, please do point me in the right direction.

[mon2]

Also post the same on badcaps. There are some gurus on this topic always there to help you nail down the details of the better caps.

[Rasz]

1 why on earth would you want to repair Pentium 4 junk? This isnt even a nice board from reputable brand (no, dell isnt), one with a lot of OC options, or some limited top of the line "enthusiast" version.

2 any low ESR caps will do and will outlive your passion for this computer.

Fitting polymer capacitors is pure audiophoolery.

[SwedishDiesel]

1. Because I like old computers and even if it is junk I'd like to get it to run again.

2. I'll be the judge of that...

Polymer caps are my choice since it's not exactly possible to get ultra-low ESR electrolytics that fit the specs and aren't counterfeit.

[wraper]

Polymer caps are my choice since it's not exactly possible to get ultra-low ESR electrolytics that fit the specs and aren't counterfeit.

Maybe don't buy on ebay but get from a reputable distributor instead?

[rsjsouza]

In my recaps I tend to stick with the same technology unless I know very well the function of the capacitor in the circuit. For the output filter capacitors in switching supplies I try to look for the lowest tan delta possible (or dissipation factor), which will influence the ability of the capacitor to withstand the high frequency switching ripple. Also, if a higher voltage capacitor fits on the space, I tend to prefer those to give an extra robustness to ripple. I pay no attention to the distance between pins, as long as there is space above them to allow the pins to be bent without compromising the rubber seal.
Regarding the capacitance value itself, obviously try to stick with the original value but at those levels a 2000uF is too uncommon when compared to a 2200uF without perceptible detriment.
Last bit not least, there's the price versus the repairability factor: in a desktop such as your Optiplex, I don't fret too much about having to recap the computer again in a few years. Things change when I have a laptop, especially old ones such as my TI Travelmate 486, where the connectors are losing their mechanical robustness and the cables and plastics are becoming brittle over time. For these I tend to search for the most durable material for the capacitors.
At any rate, good luck in your quest!

[BrokenYugo]

Polymer caps are my choice since it's not exactly possible to get ultra-low ESR electrolytics that fit the specs and aren't counterfeit.

Mouser and Digikey sell them all day long from all the Japanese brands. It's usually pretty easy to exceed the specs of stock electrolytic caps in consumer grade stuff to such an extent that the lifespan calculation of the replacement electrolytic part works out to decades of continuous use. Remember that the specified hour rating is at max temp and ripple, bring either down and lifespan goes up fast.

[SwedishDiesel]

Mouser and Digikey sell them all day long from all the Japanese brands.

Maybe don't buy on ebay but get from a reputable distributor instead?

I have been looking at reputable distributors/manufacturers, and while there are caps that will work, as far as I know they're not the most optimal thing to use in this application. I've double-checked with the folks over at BadCaps, and they confirmed that the ultra-low ESR caps used on these boards aren't readily available.

Questionable motives and pointless endeavors aside, thank you folks for your input.

[eurgenca]

Hello.
I have GX260.
Four years ago I have same problem. I put inside first caps what I found in my box. Usually 105C and now works 4 years 24/7.

[Rasz]

I have been looking at reputable distributors/manufacturers, and while there are caps that will work, as far as I know they're not the most optimal thing to use in this application. I've double-checked with the folks over at BadCaps, and they confirmed that the ultra-low ESR caps used on these boards aren't readily available.

Of course they did, its right in the name! Its like asking on Saxophonelife.org about cheap instrument for your 9 year old niece and being directed towards 4 digit Yamaha numbers. Sooner or later people start fetishizing the subject and you end up with audiophoolery. There is nothing special about old Pentium4 ~1MHz DC/DC vcore circuit.

Here is the board diagram, apparently Asus OEM https://dokumen.tips/download/link/dell-optiplex-gx260-0t606-00t606-asus-shasta-rev-x01-sch

[wraper]

I've double-checked with the folks over at BadCaps, and they confirmed that the ultra-low ESR caps used on these boards aren't readily available.

Do you want exactly the same part number or what? Why do you want exactly the same cap when there are a lot of other caps with the same or better ESR spec? Those capacitors are not special at all, not top of the line by todays standard. What original caps are, Nichicon HM/HN?

[DavidAlfa]

I've repaired dozens of mobos with that problem.
Often replaced them with something close, but not the same. Ex. 1800uF with 2200uF, or the other way around.
The store bought the cheapest capacitors in quantities of 50, 100... Not breaking our heads with 22mOhms vs 37mOhms ESR.
Mobos have multiphase regulators, when one goes off, other is turned on, so the power delivery is a lot smoother, the capacitors don't need to filter that much, they're not so critical.
For sure, if you're going for extreme overclocking under LN2,you might need the best regulation, not the case of a 15+ year old P4.

A lot of these mobos were still working fine, detecting the issue when doing maintenance, cleaning...
When measuring them, usually less than 1/5 of their nominal capacitance remained, and some of these computers were still working 24/7 as small servers.
My advice is to get anything that meets the voltage rating and the capacitance and stop overthinking, save your money for something else.

[SwedishDiesel]

I'll see to getting caps that are close enough to spec then, thank you all for your input. Apologies if I came off as idiotic.