I'm trying to fix a device that has a huge cap that leaked badly.

The leak is like molasses. Maybe thicker. And there is around 2 puddles of 2-3 teaspoons each.

I cannot clean the thing very well. So I can't read the specs on the cap so far. I am not sure if black was the original electrolytic (if it even is that) color or not. I also do not have the blueprints and the service manual i have is garbage.

So, the question is, if I do not find a way to read the marks on the cap, or if the marks are not useful for id, what is a good way to identify which fluid I am dealing with?

And what are common solvents for the most common fluids in a cap?


OK, this is a bust. I finally managed to pry trhu the black glue, and indeed, it is glue. as @DaveTweed mentioned.

When i removed the top cover, i was surprised to not find the explosion of goo inside. Instead, after removing the whole assembly, the back of the board, which is covered in glue for waterproofing (and unserviceability), had a crack and the black thing clearly oozed from that crack.

It was already solid. and the black part was mixed with the clear part, all around a burned out transformer.



  • 1
    \$\begingroup\$ Are you sure it isn't glue intentionally put there to control vibration? That sounds like an awful lot of electrolyte, even for a large cap. Can you show us a picture? \$\endgroup\$
    – Dave Tweed
    Jun 23, 2016 at 1:57
  • \$\begingroup\$ definitely not glue. it leaked far away from the board (it is mounted vertically) i am trying to clean up the smear on the air duct it leaked from before opening the EM cage that houses the cap. pics will be uploaded in a minute! \$\endgroup\$
    – gcb
    Jun 23, 2016 at 2:07
  • 1
    \$\begingroup\$ Start with Isopropyl Alcohol and if that won't do it try Acetone, smells like hell but it's powerful and shouldn't affect the PCB or any other components, but do a test patch somewhere first in case there's a reaction with the goo (unlikely, but still possible). \$\endgroup\$
    – Sam
    Jun 23, 2016 at 5:07

1 Answer 1


Do the surrounding components give you any clues as to what function the capacitor had? If they're very large and are located right next to a transformer, it's probably a filter capacitor. Filter capacitors tend not to be too picky about their values, provided they can reduce the supply ripple to a level that the electronics can handle. If it's connected next to an IC, google the IC's part number and see if you can find an application note, or a usage example. Many datasheets have this information. This will show you what devices should be connected to it, and sometimes even their values, for normal operation. Sometimes this works, sometimes it doesn't.

As for cleaning the goop, I would start by scraping as much of it off the board as possible using something like a popsicle stick or other wooden or rubber scraping tool (something soft enough to avoid scratching the soldermask and/or traces, but hard enough to remove the goop). Once you've removed the majority of it, try using 90% isopropyl alcohol and de-ionized (DI) water (careful not to let it get into any cracks that it would be difficult to get it out of). You can sometimes use other solvents, but use these at your own risk -- They may remove soldermask and even damage the traces. You can test its effects on a corner of the PCB if you want, where it won't harm anything if it does remove soldermask. Use a new toothbrush along with the isopropyl alcohol to help remove more of the goop. Finally you can rinse it with DI water and wipe it down with a lint-free cloth to soak up excess water and wipe off any residue. From there you can assess how much damage (if any) there is to the traces on the PCB, and determine whether or not it will need to be repaired.


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