trouble shooting a couple of PCB' I have managed to blow up?

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trouble shooting a couple of PCB' I have managed to blow up?

Postby stevec » Wed Oct 16, 2013 10:49 am

Hi Chaps,

I was wondering if any of you have plugged in some things with reverse polarity and typically where I should start looking for the blown components.

firstly I have a G-OSD that I managed to plug in backwards at the field and it released the magic smoke.

there are a couple of components that look like they got pretty hot but I am unable to test them because I have never faulted anything this small before.

then I just did a really dumb thing and wired the plug for a lipo powered 12v supply backwards and powered up my little SD card DVR with it and this too released the magic smoke.

As I seem to have the same problem on both bits of kit I figured I'd try and find out if there is any way to trouble shoot these IC boards before I throw them in the bin.

I have basic test tools, and multi meter, and I have a tiny little 10w soldering iron which is small enough to re attach surface mount components.

both the things I have powered up backwards work to an extent, the G-OSD will power up and light up if I use my USB programming cable ( I had re-flashed it) and the DVR LED's light up if I plug in a USB lead from a PC, I haven't tested if video goes through it when powered up from usb yet, I will try that later. but these facts lead me to believe that only the input side of things is toast and as a result probably only a couple of things have gone pop.

I am particularly interested in what sort of things I should look for and how I test voltage regulators.

any ideas would be really appreciated.
This isn't about the money, it is about the satisfaction of not throwing something away.

many thanks
Steve
stevec
 
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Re: trouble shooting a couple of PCB' I have managed to blow

Postby Oldiron » Mon Dec 30, 2013 5:28 pm

Most of the time the first thing "down stream" of the input is a voltage regulator that will blow if the thing is reverse biased. Hook it up to 12V and probe the first components after the power input to see if there is 5 or 3.5 volts coming out. Also if there are caps that got hot it is best to just replace them.

You can reflow surface mount with an iron but it is a pain! If you want to work on surface mount look up EEVblog on Youtube. Dave does a great job of explaining how and why of surface mount.
Oldiron
 
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Location: Canyon Lake Texas USA


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