Could this SMD capacitor be busted? and question about ulstrasonic cleaner  - Page 1
Forum section: electronics / repair

author: Yamin
author_rank: Frequent Contributor
timestamp: December 10, 2020, 08:02:49 pm
content: Hi everyone,I am working on a board which is in quite bad condition, bit of corrosion etc. I found this smd polarized capacitor with some kind of bulging on the side. Not sure if its some kind of glue or if the capacitor is bulged. It looks kind of white - I tried scrapping some off but it didn't work I didn't apply too much force as I didn't want to damage the capacitor. I haven't seen this kind of failure before, normally I see brownish substance leaking from electrolytic capacitors (through hole). Any idea how to confirm this? I can't get a meaningful reading from the meter, I don't want to remove it without getting a spare in. While I'm on this topic any idea where I could source these kind of capacitors seems to be a bit hard to come by.This board is a Mini-ITX motherboard (LV-67H), do you guys think that I could use an ultrasonic cleaner to clean off the gunk off this board, especially with the processor is exposed like this.Thanks in advance

author: srb1954
author_rank: Super Contributor
timestamp: December 10, 2020, 09:19:49 pm
content: Just replace the capacitor! There is a lot of corrosion round that whole area and it could have well originated from a leak in the seal at the base of the capacitor.The corrosion is very likely to be worse under the components where the corrosive agent has been trapped. I doubt whether an ultrasonic cleaner would totally clean up that mess. It might loosen up some of the corrosion products but would not necessarily completely flush those corrosion products away from underneath the components. You may have to lift other components to properly clean up all the corrosion.

author: TheMG
author_rank: Frequent Contributor
timestamp: December 11, 2020, 02:28:47 am
content: Those are polymer electrolytic capacitors, there is no liquid electrolyte to leak out, so it's definitely not the cause of the corrosion.Something corrosive has been spilled on that board, and it has attacked the aluminum of the capacitor case.With that kind of damage to the case, I would replace it regardless if it tests good or not.As for the actual repair... all components in the affected area should be removed, then the pads and traces carefully cleaned up and inspected very closely. Liquid damage can be pretty sneaky, it can for example corrode the inside of a via, creating an open circuit that is very difficult to find visually. It will also eat away at solder connections, thus the importance of removing the components and replacing using fresh solder.

author: helius
author_rank: Super Contributor
timestamp: December 11, 2020, 04:32:29 am
content: Could this device perhaps have been occupied by a mouse looking for a warm spot to sleep?

author: Yamin
author_rank: Frequent Contributor
timestamp: December 11, 2020, 12:30:04 pm
content: Thanks so much for the replies, there was a cover over the board with a fan attached. The cover rusted and the parts of loose rust got into the board due to the fan drawing in air. I suspect parts to have shorted out, as the owners were powering it up with the rust insideQuote from: TheMG on December 11, 2020, 02:28:47 amSorry for the noob question but how can you tell whether its polymer electrolytic cap (is it because of the purple colour marking?(also there is a marking which says 'PE')) Are all SMD electrolytic caps polymer electrolytic caps?Thanks so much again everyone, this is a board from a lighting console. It would have been used in harsh environments like near the beach. I think that's what have caused the corrosion.

author: wraper
author_rank: Unknown
timestamp: December 11, 2020, 12:35:29 pm
content: Quote from: TheMG on December 11, 2020, 02:28:47 amIt's not realistic. If a few component's affected, go for it. But in this case you will need to desolder a half of the board.

author: helius
author_rank: Super Contributor
timestamp: December 12, 2020, 04:53:12 pm
content: Quote from: Yamin on December 11, 2020, 12:30:04 pmSanyo OS-CON polymer caps (acquired by Panasonic in 2010) use purple ink.In this case, it is OS-CON SVPE 2.5V 390 µF, part 2R5SVPE390M.