CharlieFoxtrot wrote on Yesterday, 09:01:

It is difficult to say, my observation just is that they are not uncommon. First, I often make more or less full shotgun replacments, that is I change everything or at least large majority of capacitors. I don’t still often measure every cap I remove, often I check caps that I think are most prone to failing and important, such as VRM caps or main filter caps on PSU secondary side.

If I’d had to make an estimate, of all the failed caps I have encountered, I’d say it is at least around 10% that have failed without any visual signs. Most likely it still higher as I have bias for low esr stuff for my measurements, which are more likely prone to swelling/leaking than general use caps, which gradually just dry out or at least the chemistry fails without pressure build up. One thing to note, often the capacitance might still be in spec, but ESR isn’t. Sometimes these caps are completely dead, I can’t get any kind of measurement. I’ve even measured leaked caps that still show good capacitance, but ESR has shot up. These caps are wildly unstable, although one parameter still seems to be fine. So your basic component tester which can’t measure ESR might not even show any issues.

^ Thanks for your detailed response CharlieFoxtrot. 👍

CharlieFoxtrot wrote on Yesterday, 09:01:

TELVM wrote on 2026-08-09, 15:44:

From your experience, what's the approximate percentage of caps that get completely out of spec without showing any external visual signs of it?

It is difficult to say, my observation just is that they are not uncommon. First, I often make more or less full shotgun replacments, that is I change everything or at least large majority of capacitors. I don’t still often measure every cap I remove, often I check caps that I think are most prone to failing and important, such as VRM caps or main filter caps on PSU secondary side.

If I’d had to make an estimate, of all the failed caps I have encountered, I’d say it is at least around 10% that have failed without any visual signs. Most likely it still higher as I have bias for low esr stuff for my measurements, which are more likely prone to swelling/leaking than general use caps, which gradually just dry out or at least the chemistry fails without pressure build up. One thing to note, often the capacitance might still be in spec, but ESR isn’t. Sometimes these caps are completely dead, I can’t get any kind of measurement. I’ve even measured leaked caps that still show good capacitance, but ESR has shot up. These caps are wildly unstable, although one parameter still seems to be fine. So your basic component tester which can’t measure ESR might not even show any issues.

Honestly, measuring 20-year-old electrolytic capacitors is a pretty pointless exercise.
You're not going to solder them back in anyway, and you already have the motherboard sitting right there with cleared through-holes.

Soldering in new ones ends up being way less work overall.

shevalier wrote on Today, 04:51:

Honestly, measuring 20-year-old electrolytic capacitors is a pretty pointless exercise. You're not going to solder them back in […]
Show full quote

CharlieFoxtrot wrote on Yesterday, 09:01:

TELVM wrote on 2026-08-09, 15:44:

From your experience, what's the approximate percentage of caps that get completely out of spec without showing any external visual signs of it?

It is difficult to say, my observation just is that they are not uncommon. First, I often make more or less full shotgun replacments, that is I change everything or at least large majority of capacitors. I don’t still often measure every cap I remove, often I check caps that I think are most prone to failing and important, such as VRM caps or main filter caps on PSU secondary side.

If I’d had to make an estimate, of all the failed caps I have encountered, I’d say it is at least around 10% that have failed without any visual signs. Most likely it still higher as I have bias for low esr stuff for my measurements, which are more likely prone to swelling/leaking than general use caps, which gradually just dry out or at least the chemistry fails without pressure build up. One thing to note, often the capacitance might still be in spec, but ESR isn’t. Sometimes these caps are completely dead, I can’t get any kind of measurement. I’ve even measured leaked caps that still show good capacitance, but ESR has shot up. These caps are wildly unstable, although one parameter still seems to be fine. So your basic component tester which can’t measure ESR might not even show any issues.

Honestly, measuring 20-year-old electrolytic capacitors is a pretty pointless exercise.
You're not going to solder them back in anyway, and you already have the motherboard sitting right there with cleared through-holes.

Soldering in new ones ends up being way less work overall.

I guess he just does it as I do for empirical evidence. When I recap boards, I just measure the caps to know what state they have been in - not for re-using them, but for gaining knowledge. It's not like that more often than not the majority was just fine and got changed because I was at it already, as you mentioned, not because they really needed it.

tehsiggi wrote on Today, 07:50:

shevalier wrote on Today, 04:51:

Honestly, measuring 20-year-old electrolytic capacitors is a pretty pointless exercise. You're not going to solder them back in […]
Show full quote

CharlieFoxtrot wrote on Yesterday, 09:01:

It is difficult to say, my observation just is that they are not uncommon. First, I often make more or less full shotgun replacments, that is I change everything or at least large majority of capacitors. I don’t still often measure every cap I remove, often I check caps that I think are most prone to failing and important, such as VRM caps or main filter caps on PSU secondary side.

If I’d had to make an estimate, of all the failed caps I have encountered, I’d say it is at least around 10% that have failed without any visual signs. Most likely it still higher as I have bias for low esr stuff for my measurements, which are more likely prone to swelling/leaking than general use caps, which gradually just dry out or at least the chemistry fails without pressure build up. One thing to note, often the capacitance might still be in spec, but ESR isn’t. Sometimes these caps are completely dead, I can’t get any kind of measurement. I’ve even measured leaked caps that still show good capacitance, but ESR has shot up. These caps are wildly unstable, although one parameter still seems to be fine. So your basic component tester which can’t measure ESR might not even show any issues.

Honestly, measuring 20-year-old electrolytic capacitors is a pretty pointless exercise.
You're not going to solder them back in anyway, and you already have the motherboard sitting right there with cleared through-holes.

Soldering in new ones ends up being way less work overall.

I guess he just does it as I do for empirical evidence. When I recap boards, I just measure the caps to know what state they have been in - not for re-using them, but for gaining knowledge. It's not like that more often than not the majority was just fine and got changed because I was at it already, as you mentioned, not because they really needed it.

This is exactly why I measure them, to generally understand better how these things age in different applications and what possible quality differences there are between different brands and series, if any. After caps are removed it isn’t a big deal to measure the condition they are. And as I said, if I remove for example 30 caps, I rarely bother to meaure all, but mostly those that I think are most suspect. Which mostly happen to be low-esr stuff, main filter caps etc.

It’s interesting the first time around just for general knowledge.
A couple of times, I reinstalled name-brand capacitors that tested fine, but a year or two down the line, they started causing trouble. Over time, I came to the rule: "if you desolder it, toss it immediately."
Polymer caps, on the other hand—those really are immortal. Transplanting them from a donor board onto retro gear is a pure joy.

I always test caps i remove. In part it helps to confirm whether original caps were a potential source of issues in cases where they don't show physical signs of failure.

Sometimes caps can be wildly out of spec despite looking perfectly fine. Testing them is simply a way of diagnosing the prospective faults on a board.

What's the word on modern caps on old boards?
Is the modern ordinary cap on par with the old esr?

Got an old quadro I should recap at some point.

myne wrote on Today, 13:04:

What's the word on modern caps on old boards?
Is the modern ordinary cap on par with the old esr?

Got an old quadro I should recap at some point.

Sanyo invented polymers capacitors back in 1985.
OS-CONs were used starting with Pentium Pro motherboards.
Which modern ones are you talking about? 😀
Hybrid ones?

Jetway k8t8as s754
Vrm zone -Lelon polymer cap
By that point, the patent on some film had expired, and nobody cared about Sanyo’s crazy prices anymore. Everyone started making polymer capacitors themselves.
P.S. Silver capacitors without heat shrink tubing are actually cheap electrolytics despite their appearance. They were already bulging 10 years ago on my motherboard.

Lot’s of knowledge from this topic, I love it.

myne wrote on Today, 13:04:

What's the word on modern caps on old boards?
Is the modern ordinary cap on par with the old esr?

Got an old quadro I should recap at some point.

Depends on the board and specific application of the caps.

Replacing electrolytics with low ESR polymer caps (poly modding) is an option. I recently did this for several P4 boards.