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Old 10-30-2021, 12:47 AM   #1
SwedishDiesel
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Question Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

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; most of these were VRM caps) , 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? Iíve found ratings for ripple current, leakage current, tangent of loss angle, and dissipation factor. From what Iíve 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 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/da...0025175013.pdf
1000uf caps specs: https://www.we-online.com/catalog/da...0025175010.pdf
Original Nichicon caps specs: https://www.nichicon.co.jp/english/p...s/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/beginn...mer-capacitor/ (use the same ratings)
https://www.overclock.net/threads/ch...itors.1333093/ (use the same ratings)

Any feedback or suggestions would be greatly appreciated. If Iíve made any mistakes in here or if I've overlooked/missed anything important, please do point me in the right direction.
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Old 11-01-2021, 11:49 AM   #2
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Quote:
Originally Posted by SwedishDiesel View Post
Howdy folks,
Firstly, what exactly do I need to take into account aside from capacitance, voltage, size and lead spacing? Iíve found ratings for ripple current, leakage current, tangent of loss angle, and dissipation factor. From what Iíve read and understood, ripple current and leakage are important to take into account, but I have not been able to find an exact match.
Leakage you can ignore, Polymer caps have higher leakage than ultra low ESR electrolytic caps.
But as you have correctly found out those are not made anymore so they are not a possible choice...
The same goes for tangent of loss angle, and dissipation factor.
Well, I should not say they can be ignored completely but just as long as you stay within reason of the ESR rating of the old caps you will be fine.

Quote:
Originally Posted by SwedishDiesel View Post
Second is the half-capacitance rule - for 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.
The reason for this thumb rule is that around 10 years ago solid polymer capacitors with high capacitance ratings did not exist, or they where prohibitively expensive.
So this was just a trial run by members on this site and it was found to be true.
There is a secondary reason too and that is for VRM use the caps with the lowest ESR had high capacitance, so that is why it was used in some old designs.
And in those cases it might even benefit the control loop to go down in capacitance...
But the best choice is always to stay as close as possible to the originals, within reason as explained above.
Quote:
Originally Posted by SwedishDiesel View Post
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?
As explained above the leakage will be like this for polymer caps.
As for ripple current handling capability higher is always better, so no problems there.
The only parameter you should try to stay close to within reason is ESR.
But in some circuits, like VRM's for modern processors (the P4 is modern in this context) then you can pretty much say that the lower the ESR the better...
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Old 11-01-2021, 01:14 PM   #3
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

@Per Hansson - Thank you very much for your input. I assume the 200uf difference isn't a significant issue then for either of the caps I need to replace, as long as the ESR and voltage are (mostly) the same?
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Old 11-01-2021, 01:53 PM   #4
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Just a piece of advice - give some attention to the PSU as well... Dell uses several OEMs for their PSUs...

Depending on the one used in your particular machine, the caps may need to be replaced.

If they're Taicon but don't show outward signs of aging, then leave them (this is not a general rule, just advice for your particular case). If they're LTec, replace, whether bloated or not.
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Old 11-01-2021, 01:56 PM   #5
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Quote:
Originally Posted by SwedishDiesel View Post
@Per Hansson - Thank you very much for your input. I assume the 200uf difference isn't a significant issue then for either of the caps I need to replace, as long as the ESR and voltage are (mostly) the same?
Forgot to write that, yes caps have a tolerance of 20% so you can pretty much call that as the same rating
And +1 about the PSU, don't overlook it, and especially the small caps in such an old unit...
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Old 11-01-2021, 03:53 PM   #6
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Cheers, I'll have me a look at the PSU as well. Thank you very much for your input. It may take a bit but I'll be sure to give updates on the project when I can.
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Old 11-01-2021, 09:26 PM   #7
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Slight overlook on my end, for the smaller 1800uf caps, they have an ESR of 16. Is a difference of 4 considered "within reason"?

Do you have any advice for safely servicing a PSU? Common sense is a given, but it doesn't hurt to take precautions. I don't know if there's a way that these things can be safely discharged.
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Old 11-02-2021, 12:01 AM   #8
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

That's probably fine but as you mentioned yourself be sure that the diameter and length is not an issue as those are 10mm caps.
As for servicing the PSU it is usually quite safe to work on a working (i.e. not broken) power supply, do this:
Shutdown the computer, switch off mains power and then try to switch on the computer.
This will usually make it discharge the caps quickly.
Then when disassembling it just handle it like it could hold a charge until you reach the bottom of the PCB and can measure it.
And if you don't need to reach the bottom of the PCB just don't willy nilly touch everything in there.
Reading this thread might be useful too: https://www.badcaps.net/forum/showthread.php?t=96508
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Old 11-02-2021, 12:23 AM   #9
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Awesome, thank you once more for your input. The physical size of the caps shouldn't be an issue in this scenario, my main worry is the ratings. Everything seems to line up though so I will be ordering new caps very soon.
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Old 02-23-2022, 05:49 PM   #10
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Hello friends, it’s been a while.

The motherboard has been fully recapped, and it turned out very well. My soldering is a bit messy, but as far as I can tell there are no issues.
I did stick with the Wurth polymers I linked prior, despite some skepticism towards their capacitors. Wurth generally makes good products, so I’m not particularly worried. If in doubt, this project will serve as a case study for whether or not these caps are any good (though maybe not a great case study since as far as I know this is a relatively low-stress application). I won’t lie, I love the red color of the sleeves combined with the green motherboard.

The capacitors were assembled in China, but they came directly from Germany as a sample, so take of that what you will.

Now, time for the power supply. I've fully drained the caps inside it and opened it up, and it looks to be 95% LTec caps. They don't show any signs of failure, but I'm looking to replace them since LTec is of questionable quality and I've been advised to replace them regardless. The Nichicon caps look fine, and there's a random Taicon cap which I'm considering replacing as well.
I haven't gotten to removing the old caps so I don't have specifics just yet; once I have some more time I will take care of them.

I'm assuming low ESR ratings come into play in power supplies as well? Should I pay any heed to the tantalum caps in the unit? One tantalum has some corrosion on the leads but other than that they don't seem to show any signs of failure.

On an unrelated note, the website doesn't seem to like pictures taken from my phone, when they get uploaded they appear upside down. Not sure what causes it.
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Old 02-25-2022, 09:33 AM   #11
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Good job!
For the PSU just know that it is best to stay close to the originals ESR.
A power supply can be sensitive to changing the tuning of the circuit too much, so best to stay close in ESR...

As for the pictures it is some silly Apple thing that causes that to happen, they are incompatible with many PC based image editor software for silly reasons.
Google it if you are curious
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Old 02-25-2022, 07:56 PM   #12
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

Alright, caps are off the power supply, here's what we got:

LTec LZG:
- x1 16v 1500uf
- x1 10v 2200uf
- x4 6.3v 2200uf
- x1 25v 470uf
- x1 10v 470uf

LTec TK - these are general purpose capacitors according to the data sheet, which I found really weird since they're from a power supply. I can't find a proper impedance/ESR rating for these, so I'm not sure if it's relevant here or not. An impedance ratio is listed, but not ESR or impedance.
- x1 50v 0.47uf
- x3 50v 1uf
- x3 25v 47uf
- x1 50v 10uf

x1 mystery Taicon cap rated at 16v 100uf, with the markings (VR)P and C0537(M). I could not find any data on this particular cap, but I suspect it's another general purpose cap.

X1 Nichicon PW rated at 16v 470uf which was unfortunately damaged when trying to separate a cluster of caps held together which some sort of silicone/adhesive.

It looks that the LZG caps have a higher ESR than my leftover Wurth caps, so I don't think I'll be able to use those, which is ironic given the "ultra low impedance". I haven't looked around for replacements just yet, but I'm all ears for any suggestions.

Data sheets:
LZG: http://www.compostar.com/Ltec/LZG.pdf
TK: http://www.paullinebarger.net/DS/Lte...K%20series.pdf
PW: https://products.nichicon.co.jp/en/pdf/XJA043/e-pw.pdf
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Old 02-26-2022, 02:20 AM   #13
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Default Re: Dell Optiplex GX260 - Advice Needed for Polymodding Motherboard

They are just being silly, that is not ultra low ESR capacitors, but maybe it is the best they have so they call it that

I would recommend any of the following:
Panasonic FC
United Chemi-Con KY or KZN
Nichicon UPW

Or I mean just take whatever you can find based on current stock levels
https://www.mouser.se/c/passive-comp...acitors%7C~ESR
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