Well, generally the major suppliers have moved from very low and ultra low series wet lytics to polymers. That's probably why you have trouble finding them

People make a big deal of going with low ESR caps but I've never had issue using average or even no-name off the shelf caps on motherboards, sound cards, and video cards. PSUs may be a different beast, but I tend to not bother recapping those, they are easily replaceable with modern stuff, even the AT ones with a basic adapter.

Not possible to just replace power supply outright. Once you find one, that is not much out there and you have to still replace capacitors in these as they slowly degrade with use and time even not used.

Two reasons: I managed to find early ATX power supply with -5V for my ATX Pentium project. And 5V amp heavy for the athlon board.

Anything else, I can purchase new PSU for PII or PIII and P4 and C2D, and newer ones.

Cheers, Pentiumspeed

Power supplies and motherboards up to Pentium 3 typically do OK with Panasonic FR and FS series capacitors (or their rubycon/insert other good brand equivalents) If you find the specs for the existing capacitors in the power supplies, you will find they are typically bog standard low ESR capacitors, not the special Ultra-Low ESR motherboard capacitors. The normal Low-ESR capacitors are still in plentiful supply.

Athlon and Pentium 4 motherboards tend to be ok with a Polymod instead of the ultra low ESR capacitors you can no longer get. While their power circuit design isn't really designed with polymer capacitors in mind, in practical experience, it works fine. The capacitors that are not ultra-low ESR can be replaced with the typical Low-ESR caps that are in plentiful supply (eg Panasonic FR)

pentiumspeed wrote:

Not possible to just replace power supply outright. Once you find one, that is not much out there and you have to still replace […]
Show full quote

Not possible to just replace power supply outright. Once you find one, that is not much out there and you have to still replace capacitors in these as they slowly degrade with use and time even not used.

Two reasons: I managed to find early ATX power supply with -5V for my ATX Pentium project. And 5V amp heavy for the athlon board.

Anything else, I can purchase new PSU for PII or PIII and P4 and C2D, and newer ones.

Cheers, Pentiumspeed

Typical mini AT PSU with switch on the cable can be easly replaced with ATX power supply, yes, and -5V is really only needed for some older sound cards and on rare ocassion - motherboards.

But - and this is huuuuge but(t):

- Big tower full size AT PSU can't be really easly replaced if you care about how your build looks like.
- L-shaped AT PSUs can't be easly replaced with ATXs as well.
- XT-clone style PSUs can't be replaced for the for factor reasons too.
Not to mention countles examples of propertiary sized PSUs used in all sort of low profile cases.

So having a skill for diagnosing and repairing PSUs would be great.

If you can use an ATX with AT adapter, you can always buy a Flex-ATX PSU made for Shuttle PC's and 1U servers. Disassemble, take the board out, and fit it into the AT power supply housing with standoffs to mount it. I had to do that for my proprietary form factor IWILL ZMAXDP power supply.

appiah4 wrote:

People make a big deal of going with low ESR caps but I've never had issue using average or even no-name off the shelf caps on motherboards, sound cards, and video cards.

For older stuff, maybe. But at least when it comes to motherboards, I'd say anything post Socket 7 will need low ESR caps in order to work properly. Also, it's not just about whether it works but for how long, as no-name caps will likely die very soon by cooking themselves in hot areas such as near the CPU VRM.

Regarding the OP's question, the best way to find replacements is to get details on the caps you're replacing and buy something similar from a reputable brand. Ideally you get the datasheet of the old caps and search for a series with similar specs, making sure you use the same capacitance, same (or higher) voltage and of course an appropriate size.

Regular low ESR caps of various types are available at the major retailers (Digi-Key, Mouser, Arrow, ...). These should be good for power supplies and motherboards up until Socket 370, but it is true that ultra low ESR ones are no longer produced and these are used in later boards... you can use polymers here though, I have recently used polymers to recap an Athlon 64 board that had multiple blown ultra low ESR caps and it worked perfectly.

Also, I never order caps just for a single project, I generally wait until I have many things in need of recapping and order in bulk to get reduced prices and save on shipping costs.

A variation to the "same or higher" voltage, sometimes you can go lower if you know the circuit voltage.
In motherboards, you will have the stock 12V (typically 16V caps), 5V (6.3V caps, could possibly see 10V ones), the 3.3V on ATX or 3.3V regulator for AGP. The main place where you may often be able to lower the voltage is CPU core (post 5V/3.3V era), as the elecs are probably higher than needed - polys tend to have more low voltage options.

For high speed switching circuits, it's most important to replace the caps with something that has a similar ESR, voltage, and ripple rating. Sufficient capacitance is more important for bulk filter caps such as after the primary rectifier of any DC power supply. The hold up time is on the order of 1000x more and charge storage must be higher to match.

With regards to recapping vintage/retro PCs, I have understood that for the low voltage stuff such as motherboards and add-on cards, polymer capacitors are pretty much the best these days (long life, low ESR, no leakage of corrosive fluids), but for PSUs (at least vintage ones) not so much.

Is this still correct? And if polymer capacitors aren't a good option for recapping PSUs of old hardware, is there any other alternative type of capacitor that could be used instead of electrolytic ones? For precious vintage hardware, I'd like to avoid those like the plague, even in PSUs.

I'm asking this, because I have no experience with this yet, but would like to recap a vintage machine and I'm trying to gather the proper information about it first. Thanks.

You want to try to use the same type of capacitor the device originally had. If it originally has electrolytic capacitors, try to find equivalents.

The only time to swap a polymer capacitor in is typically for some Athlon and Pentium 4 motherboards where finding the required extremely low ESR capacitors is no longer possible. In these cases, and only these cases, you match for voltage, ESR, ripple current, and typically minimum of 50% capacity.

Recapping with polymers is especially useful for certain boards/cards that originally used electrolytic caps with extremely low ESR, starting around 2002-2003 up until the last part of the decade. These "ultra-low ESR" series usually had reduced lifespan (even for good brands) and their production has ceased almost completely by now. So polymers are pretty much the only option in this case, with the added benefit of an extended lifespan and more tolerance to heat.

For older stuff I would keep as close as possible to whatever series of capacitor was used originally. I know some people make it sound like electrolytics are a food product that will go bad in a matter of days, but if you go with well-known japanese brands they're going to last such a long time that the caps may outlive other parts of the component that will end up dying first due to age. Just look at how much stuff from the 80's or earlier that wasn't plagued by known bad cap series can still be used today!

This is especially true for power supplies: while it is a good practice to recap older units that have been running for many years under unknown conditions/heat, try to find replacements that are as similar as possible to the original parts. There are many experiences of PSU polymer mods not working properly, and even if they seem to be fine, without the proper toolset it would be difficult to know whether lowering the ESR so much has gone beyond the tolerances of the original circuit design and is negatively affecting things like the ripple voltage.

680uF solid polymer caps have worked for me at Vcore on every board I've tried them with (I think they were all P2-P4, maybe one Athlon64). That includes boards where the original caps were as much as 1800uF. I can only use them if the originals are 8mm diameter though, and most boards have 10mm caps in that location (different lead spacing).
They're difficult to install though because the leads on polymers are thick. They fit but the holes have to be well cleared first.

Only problem is I've made the mistake of using 2.5V rated caps on a couple Slot-1 boards, so I have to remember never to plug a Klamath P2 into those or I'll blow them up. It'll probably happen one of these days.

Polymers work well in general when they have an ESR which matches well with the low ESR caps they're replacing. ESR is the determining factor for output ripple and capacitance isn't very important in such cases.

Ideally we'd be able to swap every output filter cap with polys and get cleaner power, but some designs destabilize if the feedback loop impedance strays too far from original. That's why it's best to stay close to the ESR spec of the original parts.

OK, but I'm talking real vintage hardware, such as an IBM 5160. I don't like the idea of capacitors leaking and corroding PCBs, even if its not for another 30 or 40 years if I replace them today. Such hardware will be even more precious and close to antique by then.

I'd be okay with sticking to the exact kind of caps in the PSU, but in the case of the motherboard, do the ESR levels really need to match that closely?

Oh wait. The caps on the IBM 5160 motherboard are tantalum, and only the caps in its PSU are electrolytic, right?

pentium3 + socket 462 era boards were made with fake crap capacitors , so if you replace them with non low esr, it would be ok?
i was working on a soyo motherboard yesterday, most of the caps of metalic color were bad.

one thing i want to fix is an old TOPOWER TOP 420W PSU, because of it high amp 5v line. i opened it and saw about 3 bulged capacitors.
I wonder if it should be fine replacing them with other normal capacitors or i should replace those with LOW ESR ones.

any idea?

SETBLASTER wrote on 2020-08-01, 17:32:

pentium3 + socket 462 era boards were made with fake crap capacitors , so if you replace them with non low esr, it would be ok?
i was working on a soyo motherboard yesterday, most of the caps of metalic color were bad.

No, for boards of that era you really want low ESR (at least for the large caps around the CPU). No matter how crappy the originals were, their ESR was low enough back then. It's not that they were "fake", the problem is that the electrolyte used was unreliable/extremely heat sensitive which caused premature failures. There are certainly instances of caps with fake values from shoddy manufacturers, but I don't think that was common on PC motherboards by that point in time.

SETBLASTER wrote on 2020-08-01, 17:32:

one thing i want to fix is an old TOPOWER TOP 420W PSU, because of it high amp 5v line. i opened it and saw about 3 bulged capacitors.
I wonder if it should be fine replacing them with other normal capacitors or i should replace those with LOW ESR ones.

You usually want low ESR caps on the secondary side of the power supply, but generally not as low as those on motherboards. A photo of the bulging caps would help to identify what kind of replacements you need.

In nearly all cases in Switching Power Supply Units/Circuits the function of the Electrolytic Capacitors are for filtering (minimalizing the AC ripples on the DC voltages). As higher the current, as lower the needed amplitude of the AC Ripple, as highe r the needed capacity. The power dissipation on the ESR correlates with the frequency and the current. The main effect of a higher ESR is a higher temperature of the capacitor. The good message is, that the modern low ESR electrolytic capacitors accept higher temperatures.

For Recaping you should follow this rules:

• rated Voltage must be equal or higher (the higher voltage rating of the capacitor doesn’t lead to higher voltage in the circuit!)
• rated Capacity must be equal or higher (would not take more than double)
• Pitch of the legs must be equal
• Diameter should be equal or larger (better heat dissipation), depends on place around
• Hight should be equal or larger (better heat dissipation), depends on place above

As higher the capacity and/or as higher the voltage, as higher the volume/surface of the capacitor (hight and/or diamater). So for temperature critical capacitors for the CPU voltage regulators it can be smart to use capacitors with a notch higher voltage rating and so a higher hight/diameter for better heat dissipation.

You can test the thermal result in situations with high CPU load (Prime95) with your fingers on the capacitors. I use for recapping low ESR capacitors from Panasonic, Epcos and Yageo. And I never had capacitors which are not long-touchable.