Reason the small caps don't need to be replaced?

[incapacitance]

What was the reasoning for why the small caps don't need to be replaced? Will even the 100uf "Junkcon" caps stay good for a long time?

[Topcat]

Re: Reason the small caps don't need to be replaced?

What was the reasoning for why the small caps don't need to be replaced? Will even the 100uf "Junkcon" caps stay good for a long time?

I've read they use a different electrolyte forumla. I don't know how true that really is, but in all my years, I've never seen the smaller ones fail. Rarely, I've seen 470uF caps fail, usually CHHSI's on MSI boards. On gigabyte boards, I've seen those 330uF 25v choyo's fail, which I always replace with 1000uF caps. If anyone else has some more insight on those little ones, I'd be all ears.

[Rainbow]

Re: Reason the small caps don't need to be replaced?

The thing that I saw on various boards: low ESR caps are often all bad but general purpose ones are all OK. The small caps are almost always general purpose.

[PeteS in CA]

Re: Reason the small caps don't need to be replaced?

Smaller caps are usually for local decoupling or timing circuits. They aren't subjected to the kind of ripple current stress the low Z types used in VRMs are.

[cods69]

Re: Reason the small caps don't need to be replaced?

I've been wanting to post this picture for a while....this thread seemed a good enough reason.

I damaged the cap when assembling this 'Solar Cybug' kit with the iron, but it worked fine for years.
A few months ago (when discovering capacitor problems in my mobo) I noticed the bug had a leaky 1uF cap and it no longer behaved (steering circuit).
Even though the leak was obviouly initially caused by my mistake, the hole in the side of the cap where touched with the iron is far worse now than when it happened. There has been much deterioration over about 5 years and that is quite a leak of white stuff from the bung!

[dood]

Re: Reason the small caps don't need to be replaced?

Can't really blame that on the cap, though

[cods69]

Re: Reason the small caps don't need to be replaced?

Can't really blame that on the cap, though

I damaged the cap

obviouly initially caused by my mistake

I think I covered that.
In answer to the OP's question, this small cap requires replacing.

[gonzo0815]

Re: Reason the small caps don't need to be replaced?

I agree to that, but you can`t go realy for the uf rating. It is only a rule of thumb. On grafikboards there are usually many 330v caps which are indeed low esr ones, but not that often on motherboards. So in generell lock on the capazitor, if it is an low esr ones it is prone to fail, if not you can assume there are no need for that. In doubt you have to look in to the part of the cirquit. If it is not an power supply nor an switching power suply or so ones, generally esr is`t that important.

The main reason, that low esr caps are prone to fail is the fact, that the elektrolyt have to contain water to archive the low resistance. On the other hand, water and Aluminia are prone to corode and develop some H2 gas. To avoid that the manufacturer hase to add some additives to prevent that. This is pure science. But in order to make an low esr capazitor, you don`t need mutch R&D, you can bay all what is needed an fill it in a fancy capazitor wraping machine. The bad caps manufactuere do so. They know little to nothing about how to ensure quality of the raw material or how to messure that. But they can do it cheap.
No longtime tests are don etc.