Fixing a short under a can - Page 1
Forum section: electronics / repair

author: kicken
author_rank: Contributor
timestamp: July 15, 2017, 03:27:33 am
content: I have a Roku Streaming stick that hasn't been working. From some testing it seems like maybe there is a short on the board but the problem I face trying to go any further is it is under a can.I think the short might be where I added an outline. When plugging in the roku it gets pretty hot pretty fast in that location and one can even here a small noise. There's a bit of a smell there also.The can seems to be surface-mount soldered to the PCB. I tried hitting it with my iron to see if I can get it off but it doesn't seem likely, didn't seem able to melt the solder at all. So I have a couple questions regarding removing these things.I've seen in some of Dave's videos where the top of these cans seems to have been cut out. I'm guessing that is just done with something like a dremel tool?If I tried to remove the top and could fix the short, would the lack of the lid cause the device to no longer function properly due to interference? What if I removed only a small bit where I think the short is vs the whole top?I don't really anticipate actually being able to fix this thing, but I'd like to try and avoid destroying it in the process just in case.

author: DTJ
author_rank: Super Contributor
timestamp: July 15, 2017, 04:17:43 am
content: Try using a hot air gun to desolder the can.Put a wire hook under one end with a small lifting force on it.Work the hot air over the area continuously until the can lifts free.

author: Ian.M
author_rank: Super Contributor
timestamp: July 15, 2017, 05:07:42 am
content: Lifting screening cans without hot air and maybe even a board preheater is a royal PITA. Worst case, if you don't have anything better, use a pencil blowtorch, but make sure it only washes across the can, not the board. You'll probably need some Kapton sheet to slip under the edge as you get one side free so it doesn't solder itself back down when you attempt to desolder the other side.

author: kicken
author_rank: Contributor
timestamp: July 15, 2017, 02:28:21 pm
content: Quote from: blueskull on July 15, 2017, 04:21:35 amYea, that's been my assumption that some component has died in a manner that created a short. My hope is that it's something I might be able to replace and get things working again.Quote from: DTJ on July 15, 2017, 04:17:43 amIndeed I figured hot air would be the proper way to go about this. Unfortunately I don't currently have any sort of hot-air gun and am not sure it's worth the investment at this time. I'll look around at options though.Thanks all.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 15, 2017, 05:07:30 pm
content: A cooking hotplate, a cloth iron or a paint remover hot air gun might also work if you don't have access to a proper hot air station.Given the symptom you described, the main suspect might be a multilayer capacitor for filtering or bypass. Sometimes they fail by internal short circuit, and are tricky to locate, because usually there are many of them in parallel on the same power lines.

author: alm
author_rank: Super Contributor
timestamp: July 16, 2017, 02:05:08 am
content: And the trick of using an AC signal to find the short does not work well because all the caps will act like a short at AC frequencies. The only method I have found is just start desoldering caps until the short goes away. Maybe if you are lucky you could shove a bunch of current through it and look for parts heating up/voltage drops? See Dave's videos about finding the shorted power rail in the Lecroy scope for some ideas. But of course this is only relevant if you get the can off.

author: KL27x
author_rank: Super Contributor
timestamp: July 16, 2017, 09:41:19 am
content: QuoteWe can get 858D under $30.00. At this price, it's not an investment, it's an afterthought.(It also works very well.)