VOGONS


First post, by Gabriel-LG

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Last week, I bought a complete PC with a nice Asrock 939Dual-Sata2 motherboard, including a bunch of high end components of the era. 😀
However, the motherboard has some seriously bulging capacitors, so I would like to replace them, before I power up the board for the first time.
This will be my first recapping and I am not sure about the following two things:

Which capacitors to replace?
Obviously all the bad looking ones. Should I also replace the ones that look fine, but are of the same type and near the bad ones?
What about the smaller caps on the board? They all look fine, I assume they can stay, right?

What are good replacements?
Most of the bad capacitors (near the CPU) are Chemi-Con KZG 3300uF/6.3V and KZE 1200uF/6.3V. Can I replace them with Panasonic FR 3300uF/10V and FR 1200uF/25V?
I also found 2 bad OST RLP 1000uF/6.3V caps near the memory banks. Can they be replaced with Panasonic FR 1000/10v

I have some (limited) soldering experience, and access to professional equipment at my work. Any good advice is welcome.

btw. here is are pictures of the bad capacitors (they look worse in real life):

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Reply 1 of 21, by weedeewee

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I'd suggest, replace all of the capacitors.
Higher voltage is ok, lower is not,
Just make sure the footprint and height sorta match with the ones you replace, or depending on the location where they are on the board, what you can get away with.
Different capacitance can cause problems.

and ,I think, a better place to ask this would be https://www.badcaps.net/forum/

Good luck !

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Reply 2 of 21, by dionb

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Bulging is just the penultimate stage of deterioration in bad caps, they are way out of spec before they show any outward signs of damage.

In any event, replace all caps of same type as one that's bulging, so the 3300uF and 1000uF caps. I don't see any bulging on the 1200uF caps (unusual rating...), but if in doubt and you have access to good equipment, measure capacitance and ESR.

As for replacing, there are four levels there:

1) Capacitance: must be the same.
2) Voltage: must be at least capable of handling what goes over it. Sometimes board vendors over-specced caps in terms of voltage to use cheaper high-voltage caps (due to lower associated ESR) than more expensive low-ESR low-voltage ones. In these circuits, everything is derived from 5V line, so 6.3V should be good enough, anything above that is good too in terms of voltage.
3) ESR: must be as close as possible to original value, but if you have to deviate, lower is better. Finding specs of original parts could be a challenge. As explained above, a cheap hack to get lower ESR at same capacitance is to go for higher voltage rating.
4) Size: lead spacing must match, but also look out for width and height, particularly near slots and sockets. That's an argument against using higher-rated parts: they tend to be physically bigger.

Reply 3 of 21, by TheMobRules

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I would replace all of the caps if possible, the tiny ones (<100uF) should still be OK, but since you have to do the rest, why not?

Panasonic FR should be fine even though they're not as low ESR as the KZGs, I don't think you can find electrolytics of much lower ESR than those nowadays, otherwise you'd have to go with polymers. What you can do in that case is to check if there are any unpopulated capacitor spots connected in parallel with the KZGs and populate it with another cap of the same uF/V. That will lower the total ESR AND will increase the total capacitance, which is good in this case.

Other than that I adhere to the advice of dionb. If I have to add something, is that by far the most difficult part of a recap, in particular with boards from the mid 2000's or newer, is to clear the holes before fitting the new caps due to the nasty combination of very thick PCB with several layers + teeny tiny holes + non-leaded solder. If you don't have a desoldering gun it can be a grueling process, so take your time and remember to add fresh solder to the joints before removing the old caps.

Reply 4 of 21, by Gabriel-LG

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Thanks your for the replies 😀

Based on your advise, I will go with replacing all KZG an KZE capacitors, and at least the 2 broken OST capacitors. I will check the costs for replacing all remaining caps, and replace them only if the soldering goes smoothly 😉

I did some reading on the ESR and ripple part for the capacitors. I found this article to be quite insightful.

From what I understand, it is OK to use higher ripple current. Is this correct?
Changing the capacitor type or capacitance, requires knowledge that I do not have (nor will ever obtain).

The KZG replacements are indeed hard to find. The KZGs have an ESR rating of 12mOhms and 2.8A ripple current (@100kHz), while their diameter is 10mm.

At mouser, I found some Panasonics (13mOhm) and Nichicons(11mOhm) that come close, however they are 12.5mm diameter. Now there is some clearance around the KZG capacitors, but 12.5mm will be tight. Also their ripple current (3.6A and 4.1A) is way higher than the KZG's, would that still be a OK?

I will measure the clearance this weekend to see if I can fit them in. Otherwise, the 10mm 18mOhm Panasonics FR will have to do.

Reply 5 of 21, by Gabriel-LG

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OK, I just measured on the board and 12.5mm is not going to fit

The Panasonic FR is not an option, because the ripple current rating is too low.

The UHW series from Nichicon may work (despite the higher ESR), but I can only source them from the US, so shipping+clearance+taxes will be too high.

I am afraid my 939Dual-SATA2 is R.I.P. 🙁

Reply 6 of 21, by ODwilly

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Hey you never know, you might stumble across a dead board with good caps that will work with it in the future, or find the right replacements somewhere unexpected. Throw it in a anti-static bag and save it for later 😀

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Reply 8 of 21, by pentiumspeed

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Polymer capacitors is good way to get as well. Reason for very high uF was to get ripple current high enough using electrolytic capacitors back in the day.

Cheers,

Great Northern aka Canada.

Reply 9 of 21, by Gabriel-LG

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ODwilly wrote on 2021-02-28, 21:07:

Hey you never know, you might stumble across a dead board with good caps that will work with it in the future, or find the right replacements somewhere unexpected. Throw it in a anti-static bag and save it for later 😀

I was planning to do just that 😀

mr.cat wrote on 2021-02-28, 21:44:

What about polymodding? That also ruled out?

pentiumspeed wrote on 2021-02-28, 22:24:

Polymer capacitors is good way to get as well. Reason for very high uF was to get ripple current high enough using electrolytic capacitors back in the day.

I did not expect polymere caps were be possible. So I did some investigating, here are my results:
The KZG capacitors are on the VRM output side. The capacitor voltage rating can be much lower here (as VCore does not exceed 1.5V for socket 939). Using polymer caps here should be possible.

  • If the switching frequency of the VRM controller is low, then the same capacity is needed (3300uF).
  • If the switching frequency of the VRM controller is high, then less capacity will do.
    how much lower is safe?
    Should ESR be lower for the lower capacity to work?
    Is higher ripple rating required in this case?
  • If the ESR to too low, then the VRM controller will start oscillating (loop feedback)
    how much lower would be safe?
  • The 939Dual-SATA2 uses an STM L6711 3 channel VRM controller switching at 150kHz (450kHz ripple).
    This is considered high frequency (right?)
  • Choose the wrong values and it will fail after a short period of time. Also polymer caps fail short (opposed to open for regular electrolytes). This will cause smoke...

The only place selling Radial Polymer caps here, appears to be Farnell. And these 4 are the only candidates (>= 1500uF, physically fits and in stock):

Which ones of these (if any 😜) would be viable candidates?
For reference the original Chemi-Con KZGs are 3300uF, 6.3V, 12mOhm(!), 2.8A and 2000 hours@105C.

I am spending way to much time on this, for it not to work 😉

Reply 10 of 21, by weedeewee

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one of the last times I recapped a board, I took the SMD types, bent the legs straight, removed the plastic baseplate and used them as through hole components. board is still working, had a Q6600 cpu.
I also didn't care about the ripple current rating, just same pitch, diameter, height, capacitance, voltage, temp rating, and low ESR, 10 20 whatever.
also nice quality brand, not some chinese thirteen in a dozen brand name.

So how about this? https://nl.farnell.com/panasonic/eeufr0j332l/ … f-20/dp/2217556

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Reply 11 of 21, by johnsonlam

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1) Better use same capacitance "3300uF", 1500uF is too small.
2) Try other vendors (RS, Mouser, Digikey) for same capacitance
3) IMO, not the ESR value is important but not a critical part, since modern electrolytic ESR value not too bad
4) Temperature is a factor but it can be solve by improving cooling inside chassis, so even 85C will be fine, otherwise even 105C still shorten it's life
5) Definite not to use Mainland Chinese brand, it's suicide

Reply 12 of 21, by auron

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weedeewee wrote on 2021-03-01, 22:18:

one of the last times I recapped a board, I took the SMD types, bent the legs straight, removed the plastic baseplate and used them as through hole components. board is still working, had a Q6600 cpu.

that's bad practice that can easily cause the legs weaken and snap, as they aren't meant for doing that... not to mention, there is hardly a reason to use SMD electrolytics instead of thru-holes in the first place - they are well inferior in terms of ESR and ripple specs as any datasheet will tell you.

Reply 13 of 21, by Gabriel-LG

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weedeewee wrote on 2021-03-01, 22:18:
one of the last times I recapped a board, I took the SMD types, bent the legs straight, removed the plastic baseplate and used t […]
Show full quote

one of the last times I recapped a board, I took the SMD types, bent the legs straight, removed the plastic baseplate and used them as through hole components. board is still working, had a Q6600 cpu.
I also didn't care about the ripple current rating, just same pitch, diameter, height, capacitance, voltage, temp rating, and low ESR, 10 20 whatever.
also nice quality brand, not some chinese thirteen in a dozen brand name.

So how about this? https://nl.farnell.com/panasonic/eeufr0j332l/ … f-20/dp/2217556

I am afraid, I do not share your soldering skills 😐 so I will stick with the original footprint.
The Panasonic FR has too high ESR and too little ripple current. Knowing Asrock, they did not overdimension these capacitors in any way. The fact that they put in name brand, low ESR high ripple capacitors on this location, is an indication that this is really needed. The fact that they popped despite of good airflow confirms that there is little margin 😉

johnsonlam wrote on 2021-03-02, 08:31:
1) Better use same capacitance "3300uF", 1500uF is too small. 2) Try other vendors (RS, Mouser, Digikey) for same capacitance 3) […]
Show full quote

1) Better use same capacitance "3300uF", 1500uF is too small.
2) Try other vendors (RS, Mouser, Digikey) for same capacitance
3) IMO, not the ESR value is important but not a critical part, since modern electrolytic ESR value not too bad
4) Temperature is a factor but it can be solve by improving cooling inside chassis, so even 85C will be fine, otherwise even 105C still shorten it's life
5) Definite not to use Mainland Chinese brand, it's suicide

According to Badcaps (PPBONEZ, Topcat and more) for polymodding VRMs roughly half the capacitance should be used (this applies to VRMs only). The low ESR is needed on the VRM output side especially, because of the high fluctuations in current. Higher ESR caps will pass (too) much of the noise, while heating up due to the internal resistance.
Since the rise of the polymer caps, electrolytic ESR has actually regressed.
I have tried any vendor I could find. The only vendors with (somewhat) decent electrolytics are US based, and the shipping+clearance costs alone are over 33 euros, then I still have to pay for the parts plus taxes. This is a no go for me.

With regards to Chinese brands, I could not agree more...
I think I will take a gamble with either the Wurth or the KEMET polymer capacitors. Both are respectable brands; KEMET is cheap and has a matching ESR, Wurth has a higher capacity.

Reply 14 of 21, by weedeewee

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FYI, your idea of high end, and the quality of those caps seems misguided. which makes me doubt the validity of any claims in the datasheet. Especially considering the period the board was new.

https://www.eevblog.com/forum/repair/kz ... t-happen)/ and there's also references to the badcaps forum.

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Reply 15 of 21, by pentiumspeed

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Actually, ESR is important than uF. If the spot is too few, you have to make up for the loss by using largest uF possible and use polymer.

Even back in the days of CRT, the vertical sweep circuit depends on ESR of the one capacitor (actually small than you think, was 100uF 35V) to help with return of the beam back to top with a sharp kick in short pulse of double the voltage plus cap's stored voltage.
Same with power supply that used high frequency SMPS (15KHz and up). The budget TVs used the flyback transformer and second transistor for horizontal drive, as a SMPS instead via a B+ voltage regulated in time with 15KHz using separate SCR chopper. Hence the flyback is the tank & capacitances.

Cheers,

Great Northern aka Canada.

Reply 16 of 21, by auron

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weedeewee wrote on 2021-03-02, 15:48:

FYI, your idea of high end, and the quality of those caps seems misguided. which makes me doubt the validity of any claims in the datasheet. Especially considering the period the board was new.

https://www.eevblog.com/forum/repair/kz ... t-happen)/ and there's also references to the badcaps forum.

KZG was simply a bad series from an otherwise well-regarded manufacturer, but that wasn't really well known until years after the fact. if you look up old topics ca. 2006 on badcaps, that series was recommended for recapping jobs back then.

i too wouldn't at all be surprised if panasonic FR would work just fine (the board probably worked for quite some time with out-of-spec caps, as well), but there is nothing particularily misguided about trying to match or exceed those original ripple specs, either (with lowering the ESR it depends on the circuit).

Reply 17 of 21, by Gabriel-LG

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The replacement caps came in 😀 So hopefully, I will get a chance to recap this board next week.
The KZG caps will be replaced with Wurth polymers. For all other caps, I have Panasonic FR replacements (kind of a coincidence that the FR specs fitted nicely everywhere).

I will post an update with pictures when it is done.

Reply 18 of 21, by Gabriel-LG

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Yesterday, I was able to do the recapping. All but 4 capacitors are replaced now (I ran out of time for the last 4, they are not significant so maybe someday I will replace those as well).
The capacitors for the VRM output (the KZG) were a real pain to remove. The (vcore) PCB plane is layed out as a heatsink and the capacitor footprints have no thermal reliefs 🙁
In the end I managed to remove them by preheating the board to 150C and desoldering them with a 120W desolder iron at 400C for about 30 seconds (way longer ad hotter, than I was comfortable with). But hey, no visible damage.
The rest also took way longer than I had imagined.

This is a picture of the board after placing the new poly caps. (I forgot to take pictures after it was completed, due to time and stress 😉, it built in now...).

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The end result: it works like a charm 😁 😁
I am not able to measure the Vcore ripple, because that requires some special equipment.
Instead, I plan to do some stress tesing and overclocking, to see how well it holds up.

These are the capacitors I used for the replacement:
- (6x) 3300µF, 6.3V, Ø10mm, 5mm footprint: Würth WCAP-PT5H 87023517500 (2000µF, 6.3V)
- (5x) 1200µF, 16V, Ø10mm, 5mm footprint: Panasonic EEUFR1E122LB (1200µF, 25V)
- (2x) 470µF, 16V, Ø8mm, 3.5mm footprint: Panasonic EEUFR1C471 (470µF, 16V)
- (23x) 1000µF, 6.3V, Ø8mm, 3.5mm footprint: Panasonic EEUFR0J102 (1000µF, 6.3V)
- (11x) 100µF, 16 V, Ø6.3mm, 2.5mm footprint: Panasonic EEUFR1E101H (100µF, 25 V)

Also I populated the northbridge fan header, because the northbridge itself and the mosftets next to it get really hot (popped caps and discoloration on the back of the board as a result). I will mount a 40mm fan there as soon as I have one.

Reply 19 of 21, by mr.cat

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Cool, congrats on the mission accomplished! Is it so expensive as they say worth the expense?
EDIT: pentiumspeed you're right, totally worth it!!

Last edited by mr.cat on 2021-03-24, 22:31. Edited 2 times in total.