Bad electrolytic caps

[Tantalum7]

I searched several sources but couldn't seem to find this question answered specifically:  what would be the warning signs of bad electrolytic caps in older effects boxes?  It there a way to check old caps on the PCB without removing them?

Thanks

[bluesdevil]

Not a pedal, but may apply: When my computer was shutting down on me without any reason, I checked the motherboard and a lot of the electrolytic caps were either bulging on top or leaking (dried up crusty stuff). So, I guess that would be the obvious physical signs of bad electro caps.
    I think I read somewhere that a ground hum like sound could be a sign of a bad cap, but that might be the power filtering section of tube amps... can't remember exactly! If you are doubtful of a electro cap, you can try placing a .1uf (or less) across it's leads (if possible) and check to see if you hear an improvement. If the fluid is drying up it may cause a thinner sound, I believe.... not an expert here, so please correct me if I'm wrong, somebody.
   

[bbmonster]

I had a wind like noise, sounded like a constant blowing, not a hisssss, more like shhhhhhhhhh. The thread at http://www.diystompboxes.com/smfforum/index.php?topic=66402.0 is what tipped me off to a bad cap.

[JKowalski]

When capacitors get old, they get lossy, lose capacitance, become a short circuit, or heat up (during significant loss). The heating up may also caused the aforementioned bursting, as in blue's post - the liquid inside the cap boils and the gas expands. Usually this happens at the top of the capacitor. (I accidentially ran a capacitor 4V above the ratings, and that was quite a sight. Starts to bulge outward on the top, and them BAM, a geyser! wasnt my proudest moment XD This can happen just because of aging too, not necessarily just because of overvoltage)

Pretty much, there is no way to tell unless the capacitor is physically damaged or leaking. Typically, if your circuit is old, and has been unused for a long time, you should probably replace them. It should always be the first thing you do when troubleshooting old electronics and there does not seem to be a totally obvious solution.

[frank_p]

http://www.diystompboxes.com/smfforum/index.php?topic=65451.0
http://www.diystompboxes.com/smfforum/index.php?topic=72006.0

[Tantalum7]

Thanks for the wealth of information.  I had an old Boss Noise Gate that seemed to produce at least as much noise as it gated.  I checked the board on it and noticed that there were over a half dozen electrolytic caps.  Since the unit was approaching 20 years in age, I thought that those caps were a good place to start checking, but I didn't want to replace them all if I didn't have to.  Now at least I have suggestions for how to address the issue.  Much appreciation for the help.

s

[JKowalski]

http://www.diystompboxes.com/smfforum/index.php?topic=65451.0
http://www.diystompboxes.com/smfforum/index.php?topic=72006.0

I forgot about those! I read up one them a long time ago and thought "i should build one of these" and never thought about them again. XD

Thanks Frank! I'll have to make one now.

[frank_p]

Yeahhh:  -Now-  for me is a very long word...   

[Tantalum7]

I guess the search criteria I was using weren't turning up the goods.  I never noticed those links when I was looking before, but I knew the subject must have come up before.

[JKowalski]

Yeahhh:  -Now-  for me is a very long word...   

Haha, same here.