Blasted caps! - Page 1
Forum section: electronics / general

author: elliot42
author_rank: Contributor
timestamp: September 28, 2012, 12:02:04 pm
content: So my NetComm Powerline network adapter stopped working last night and it smelt like burningAfter checking that it was out of warranty I cracked it open and the source of the smell was obvious. One of the caps has completely vaporized, taking part of the cap opposite and the surface of the PCB with it. It's a 400V 10uF cap that I guess is a filter cap on the 240V rail.Surprisingly, there's a fuse in there that's still fine; not sure why it's not blown...My question is it worth fixing? Or would it be possibly unsafe considering it's position and the damage it's already done to the board?Some pictures are attached, I've cleaned the board a little in the third.EDIT: I meant to post this in General Chat, but I guess here will do.Fixed that for you.

author: G7PSK
author_rank: Super Contributor
timestamp: September 28, 2012, 12:28:59 pm
content: From your picture it looks like the pcb track blew out as well or possibly first. Clean off the carbon residue before deciding.

author: Neilm
author_rank: Super Contributor
timestamp: September 28, 2012, 05:13:22 pm
content: It could have been a transient on your power supply. This could cause a flash over. I couldn't see the fuse but it could be a resettable one that will stop the arc but will heal and not show a problem when cooled down.Neil

author: tom66
author_rank: Super Contributor
timestamp: September 28, 2012, 05:35:35 pm
content: Is that a Samxon or Capxon? I have seen both 400V variants of those cap makes suddenly fail short circuit, leaving a big burn on the PCB... Not sure what causes it, seems like a bad thing!

author: elliot42
author_rank: Contributor
timestamp: September 29, 2012, 12:24:12 am
content: All the electros on the board are branded "Jackcon".Here's a pic of the cleaned up crater it madeIt doesn't look like it's damaged anything other than the cap opposite (which I've removed also) and a few layers of fiberglass underneath it.The pads have indeed been damaged; the one for the positive terminal has just gone and part of the other has lifted. The ground planes at the negative terminal are joined at the IC so it shouldn't matter that it's damaged. Unless it's going to cause arcing or something nasty.The fuse is just a regular ceramic fuse mounted vertically and gooped to a nearby cap. I've pointed it out in this picture.

author: Bored@Work
author_rank: Super Contributor
timestamp: September 29, 2012, 09:40:40 am
content: Quote from: elliot42 on September 28, 2012, 12:02:04 pmYou know the old joke? The job of all the components is to protect the fuse.Seems to have worked perfect in your case.

author: tom66
author_rank: Super Contributor
timestamp: September 29, 2012, 09:51:43 am
content: Hmm, never had a Jackcon primary fail, but only seen a few low voltage Jackcons... those were bulged. They were in a power-line ethernet adapter thing.

author: elliot42
author_rank: Contributor
timestamp: September 30, 2012, 04:49:25 am
content: This is in a power-line ethernet adapter too.I replaced the bad caps, plugged it in, and.... nothingNo light from the LEDs, no new burning smell, nothing. I guess something else got fried that's not quite as obvious as a vaporized capacitor.

author: mariush
author_rank: Super Contributor
timestamp: September 30, 2012, 05:24:24 am
content: Check the fuse (or the resistor acting as fuse).

author: SeanB
author_rank: Super Contributor
timestamp: September 30, 2012, 05:56:31 am
content: Open fusible resistor and bridge rectifier then as well. The energy had to come through them, and they blow faster than a fuse as well.