Leaky cap questions

[80sJunior]

Now that I have thoroughly cleaned out my JVC JA-S55 integrated amplifier, I notice that there are areas around the caps (puddles), especially the smaller ones, were a brown substance covers the board. In some instances, this stuff is into adjacent conductors, with a some showing signs of corrosion.

A few questions on this:
1) Is this residue a conductor?
2) Should I clean it off and if so, with what?
3) The worst ones are the smaller caps on the volume, bass/treble and main board. The big boys in the power section don't show as much of this. Is it likely that I will have to replace all these caps?

Thanks!
Junior

 

[TheAudiotech]

corrosion

No, it is not conductive, I would suggest acetone to clean it (keep it away from plastic cosmetics). You normally don't have this problem with larger caps.

Steve

 

[ferninando]

are these brown puddles of substance on the component side or circuit side of the boards? could be rosin residue from soldering. If so it's non-conducting. try picking it with a pointy tool and se if it chips off. If it does it's rosin. If it's gooy like congealed old oil then it's something else. Caps that leak are usually tubular types, silver in color and electrolytics and they are polarized. Old big can type electrolytics(filter caps) can leak. Non-electrolytic caps don't have a "liquid" dieelectric material and don't leak. Hope this sheds some lite on your problem.

 

[80sJunior]

Thanks for the replies. I had some concerns about the brown "puddles" around the base of the caps (component side) that flowed into other components. In particular, those that showed signs of corrosion.

I took my smallest precision screw driver and was able to lightly scrape and chip away the residue. None of it was oily, but if it is the soldering residue, it appears to be corrosive.

So much to learn... Good to be starting out with a budget buy project!

Regards,
Junior

 

[Haoleb]

The electrolytic substance inside caps is corrosive, so i would have to guess that they may be leaking. I dont believe any glue used to fasten them before soldering would have corroded anything. If they are leaking, you probbly should replace them as preventive maintenance, and because they arent supposed to do that.

 

[ferninando]

only electrolytic caps have corrosive electrolyte. None of the others do. They use either mica or film. So don't go changing all caps. Determine if a cap is actually leaking before removing it. The leakage will be oily. Rosin core solder is non corossive and mfrs would not use acid core solder. If someone has worked on the unit and didn't know what they were doing they may have used acid core solder, but not very likely.

 

[glen65]

Pull the caps in question out.

Clean the entire area.

Install new caps.

 

[TheAudiotech]

cap leakage

Electrolyte leakage is not brown, if a cap was leaking you would have some functional effects.

Steve

 

[80sJunior]

Okay, so it would appear there is a difference of opinions on this. The caps in question are vintage 1979 - 1982 (amp production years). These are 35v 220mf, 50v 110mf and 63v 470mf capacitors and look similar to the blue w/gray markings I can buy at Rat Shack today.

So, the question is... Is there anything in these to leak out???

Funny story... I'm a bit ham fisted and working on delicate items in close quarters is a challenge for me. Recently, when I was testing an energized car stereo amplifier, I accidently shorted a soft turn off circuit cap to the 12vdc main power lead. Duhho! The thing exploded like a substantial fire cracker, covering me and the interior of the car with a pale yellow fiberous material. Lucky not to have lost an eye! Cleaned it up as thoroughly as possible, but now I'm beginning to think I better go back in there and clean it up better. The idea of holes in the leather upholstrey of my Porsche, has got me worried. :worried:

Regards,
Junior

 

[Ed in SoDak]

Are you sure you're not looking at an anti-vibration coating? It's common with high-freq. caps to put some goop on them to help quell the oscillations. In severe cases, like on HV coils in TV's, it can fracture the solder joint. The goop can be anything from hot glue to adhesives and can be brown to begin with or get brittle and brown with age.

Certain Kenwood Ham transceivers used a kind of goop that did become conductive and corrosive after time, as it absorbed moisture, this ruined the board and caused the unit to fail. But usually it's non-conductive, even if it's no longer elastic enough to do its job.

If you're having a problem in this area, I'd suspect cold or fractured solder, possibly bad caps also. You could heat your meter probes, jab them in the stuff and try to take a resistance reading on the highest range.

If it appears to be antivibration, you may want to use Elmer's, hot glue or something to replace it.

-Ed

 

[outlawmws]

I'm also thinking a bonding agent of some sort. Sansui is infamous for thier component adhesives, as it gets corrosive/conductive as it ages? One of the two, if not both...

 

[TheAudiotech]

Brown Gunk

Yes that is very true, they even glue caps down so they can be securely soldered in the vat when manufactured. Why did'nt I thunk of that? :scratch2:

Steve

 

[Ed in SoDak]

Before I knew it had a purpose, I used to try to remove it all. Now I only do if it looks like it's making other problems.

-Ed