Just a little bulge = bad caps?

[BenMcClure]

The two Lelon brand filter caps in the power supply section of my stereo amplifier have very slightly (and unevenly) - but definitely - rounded tops. I see on this site that Lelon is a known bad brand. This amp is only like 10 years old, and is a typical solid state class B design; for this type of circuit, from what I've read online, this shouldn't typically be expected, so I just wanted to throw this ultra noob question to the experts and see whether I should recap, or if I'm just making up problems. Thanks.

[budm]

Re: Just a little bulge = bad caps?

"but definitely - rounded tops. I see on this site that Lelon is a known bad brand. This amp is only like 10 years old, and is a typical solid state class B design;" Yes, recap, its 10 years old, by the way its Class A/B, Class B will sound real bad.

[stj]

Re: Just a little bulge = bad caps?

rounded PLASTIC tops or metal ones?

[budm]

Re: Just a little bulge = bad caps?

Pictures would help.

[BenMcClure]

Re: Just a little bulge = bad caps?

Thanks for your replies. The tops are thin black plastic, so I don't know exactly what is going on underneath the plastic. I'll get some photos this evening to show what they look like.

[ReeceyBurger123]

Re: Just a little bulge = bad caps?

Thanks for your replies. The tops are thin black plastic, so I don't know exactly what is going on underneath the plastic. I'll get some photos this evening to show what they look like.

Normally the plastic cap on th top of the capacitor tends to bow and dome over time due to heat ect. Best bet is to see if you can push down on them, If you can push them down most likely the cap is good if you cant and there is obvious pressure under the plastic cap remove but cutting it off it and see if the capacitor can is actually bulged. Most likely the cap is fine.

[SteveNielsen]

Re: Just a little bulge = bad caps?

Pull them out and test them.

[BenMcClure]

Re: Just a little bulge = bad caps?

I pressed on the plastic tops and they didn't give, so I removed them to see what's underneath. As you can (hopefully) see, the metal tops are slightly bulged. I think the schmutz is maybe adhesive to adhere the plastic tops to the metal, but I can't tell...I couldn't see any actual break inthe metal.

[kc8adu]

Re: Just a little bulge = bad caps?

those are shot.the schmutz is leaked electrolyte

[stj]

Re: Just a little bulge = bad caps?

yea, those are done.
the electrolyte leak is in the center of the longest pressure release-section - dead givaway.

[BenMcClure]

Re: Just a little bulge = bad caps?

Well, OK, then! Thanks, fellows. It's nice when the answer is so straightforward!

[ReeceyBurger123]

Re: Just a little bulge = bad caps?

They are failed alright :L

[Topcat]

Re: Just a little bulge = bad caps?

yup, goners.

[eccerr0r]

Re: Just a little bulge = bad caps?

The curiosity is: what made you look into this problem?

Usually amplifiers, to get rid of any noise, do not use switching PSUs and use heavy linear filtering supplies. That's why those caps are huge 0.01F units, but at least they usually are under lower stress.

Not to say they can't fail or are unaffected by the electrolyte problems, but are you getting 60/120 cycle hum in your speakers or something? Or does it sound OK, but you just look at them and appear odd?

[slowboy]

Re: Just a little bulge = bad caps?

thanks for pictures

[BenMcClure]

Re: Just a little bulge = bad caps?

eccerr0r:

I started noticing that I was getting light buzzing out of the speakers when the input attenuation pot was turned to about 6 or 7. I searched high and low for the cause, but couldn't find anything in terms of grounding or anything. I'm new to a lot of this, so it wasn't until reading about bad power supply caps that I realized they could even be a source of excessive hum (not to say that's necessarily the cause of my issue).

So long story short I was just kind of digging around and noticed they looked suspect.

[eccerr0r]

Re: Just a little bulge = bad caps?

Well, the other thing is that most audio/linear amplifiers have a specification to reject power supply noise too, so hum can be attenuated through this as well.

I still kind of find it weird that if the caps really did rupture, why didn't at least one rupture at the vent lines' weakest point - where the two lines meet...

[stj]

Re: Just a little bulge = bad caps?

the weakest point is the point that the cut is deepest., not at the junction.

[Behemot]

Re: Just a little bulge = bad caps?

What's the voltage?

[BenMcClure]

Re: Just a little bulge = bad caps?

There was and is about +/-53v across the capacitors under power. The old Lelon caps I asked about originally were 50v, 85C devices. I replaced them with Vishay/BC Components 63v, 105C units, so I guess even if the old ones were still "OK" by some measure, it's better to have 10-year-newer ones from a better brand with higher ratings.
(I assume it's a better brand; I see Lelon on the bad caps thread but don't see anything about BC in the good or bad brand threads, but the ones I got were the only ones I could find with those specs that would fit in the case).