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Would the discoloration around the negative lead of these capacitors be a sign of failure? If so, why would the negative lead darken instead of the positive - or both leads.

pic1 pic2

They are Maron EFM 35 volt 680 uF electrolytic capacitors.

JRE
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Firewolf
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    I can never remember if its the equivalent of galvanic corrosion provided by the excess negative charges at the negative terminal that causes this, or if its some other chemistry. It doesn't help it also depends on what elements are involved the one with the residue is the one that produces solid compounds and the one without the residue is the one that produces gaseous compounds. Or whether it's more like batteries where there the reaction at one terminal produces gas which then reacts with other stuff to produce solid compounds. – DKNguyen Apr 30 '21 at 23:59
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    It's more likely that you applied more heat to the negative terminal in order to desolder it, because it was attached to a large ground plane. – Dave Tweed May 01 '21 at 00:09
  • It's spelled electrolytic. and μF, not uf. – Hearth May 01 '21 at 00:13
  • @DKNguyen that's an interesting thought, and would explain why it's only on the negative terminal. Not sure if the electrolyte in the capacitor has those kind of chemicals. – Firewolf May 01 '21 at 00:59
  • @DaveTweed - I agree that was my thought as well. – Kevin White May 01 '21 at 01:03
  • @Hearth my bad. I've edited the post to fix the typo. As for the uF, I don't think my phone keyboard can even type that character. – Firewolf May 01 '21 at 01:08
  • @DaveTweed you might be on to something. Ill heat up the positive lead for a while on my soldering iron and see what happens. – Firewolf May 01 '21 at 01:10
  • @Firewolf At the very least, capitalize the F! ...I hate that μ isn't on any of the common keyboard layouts other than the Greek one. – Hearth May 01 '21 at 02:44
  • @MichaelHarvey that’s a bit redundant. Do you have a suggestion as to how to easily generate this character on a phone keyboard? – StarCat May 01 '21 at 10:11
  • @MichaelHarvey, Thanks for proving my point ;-) My question was about a phone keyboard. On Windows or Linux, Alt codes are hardly intuitive and do not work at all on a laptop without a numeric keypad. I usually copy & paste from a website or a piece of text if I really need to. – StarCat May 01 '21 at 12:35
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    For comments, another trick is to type µ into an answer box and then copy-paste the resulting 'μ' from the preview area. You can do the same thing with ° (°) and ± (±). Of course, when you're writing a question or answer, just use the HTML entities to begin with. – Dave Tweed May 01 '21 at 12:46

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