What happened here then? - Page 1
Forum section: electronics / projects

author: itdontgo
author_rank: Regular Contributor
timestamp: October 15, 2014, 09:03:27 am
content: Hi folks. Anyone care to give me a second opinion on how this failed. I've got a good idea but to avoid confirmation bias I'll let you give an opinion. What do you think caused this to fail?

author: Kjelt
author_rank: Super Contributor
timestamp: October 15, 2014, 09:12:53 am
content: Someone put AC mains or 24V AC on the low voltage DC input?

author: Rerouter
author_rank: Super Contributor
timestamp: October 15, 2014, 09:15:36 am
content: As the third image is so blurry its near impossible to tell, but looks like an 0805 smd resistor popped in a big way from excessive heating, first thought would be what function does it serve? if it is there to pull the 24V supply wire to ground weakly, check that the value was correct,

author: Artlav
author_rank: Frequent Contributor
timestamp: October 15, 2014, 09:16:19 am
content: The stains seem like battery electrolyte to me.Some sort of spill, corroding or shorting the supply pins?The last picture is badly out of focus...

author: bktemp
author_rank: Super Contributor
timestamp: October 15, 2014, 09:20:44 am
content: Since only a resistor and now semiconductor seems to be blown, it is impossible to tell without having the schematic of that section.

author: SL4P
author_rank: Super Contributor
timestamp: October 15, 2014, 09:29:13 am
content: Strange photos - what are they showing?In one I see what loks like a smoked SMD component in the near corner, and in the second a blob of something under the connector on the opposite end of the connector pins-strip.As Artlav said - one looks like electrolyte / liquid spill - and the next like an over wrought component. Perhaps (water) ingress, short, then smoke.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 15, 2014, 09:45:56 am
content: I would also say, that someone hooked a higher voltage up to the input and ground.

author: SL4P
author_rank: Super Contributor
timestamp: October 15, 2014, 09:50:45 am
content: http://youtu.be/PtcPAUxKJoQThere's your problem

author: itdontgo
author_rank: Regular Contributor
timestamp: October 15, 2014, 10:09:49 am
content: Haha!What I think happened, and you're right the photos are rubbish, is that something like a battery or electrolytic has leaked and it's flowed down the ground wire to the PCB and damaged the power supply section. It's worked fine for a year in it's installation and I have no reason to believe the power exceeded 24VDC which is the maximum.The gruesome looking resistor is a 150R 0805 which is used to set the voltage output from the buck regulator. There is also a cap and a 100k output enable resistor none of which should ever be able to get remotely hot. The zener protecting the GSM module has a nice little hole in it so I assume the output of the buck has gone high at some point and ruined everything.It's clearly corrosion and not by water. However I wanted to hear that from someone else as the customer says this is impossible!

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 15, 2014, 10:21:49 am
content: Not sure its a spill or leak of any kind, you can easily check by looking at where it's installed.The blob looks like PCB lacquer (from the PCB fab process) has been melted and flowed downwards. You have a large ground plane by the looks of it and a 24V DC terminal next to it. Looks like some high power has been dissipated there, possibly from incorrect voltage applied to the DC terminals.

author: Codemonkey
author_rank: Regular Contributor
timestamp: October 15, 2014, 10:49:58 am
content: Quote from: bookaboo on October 15, 2014, 10:21:49 amI disagree. A board that has been in service for a long time running too hot would be discoloured over the whole area that was hot, especially if hot enough to melt the solder resist!

author: VK5RC
author_rank: Unknown
timestamp: October 15, 2014, 11:17:29 am
content: Could the discolouration be fungal growth in pooled water, a lot of 'water proof' devices once the leak are really good at holding onto the stuff.

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 15, 2014, 11:27:11 am
content: Ah, yes I read the OP second message that it was installed for a long time. Still find that blob very strange though.

author: mikerj
author_rank: Super Contributor
timestamp: October 15, 2014, 11:29:11 am
content: Looks very much like corrosion to me. Is the inside of the 0v screw terminal badly corroded as well? That would fit with the ground wire being the ingress point of something nasty.

author: itdontgo
author_rank: Regular Contributor
timestamp: October 15, 2014, 12:22:25 pm
content: The guy is adamant nothing can have leaked on it but it certainly looks like corrosion. I don't suppose something blowing up could look like corrosion? The electrolytic is fine.

author: itdontgo
author_rank: Regular Contributor
timestamp: October 15, 2014, 12:24:57 pm
content: Same camera but with a magnifying glass in front of the lens btw! The blob on the solder mask is in an area with no parts which could not get hot.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 15, 2014, 02:17:38 pm
content: If something leaked in to the case / housing, you should be able to see it on the case as well.

author: MK
author_rank: Regular Contributor
timestamp: October 15, 2014, 04:06:01 pm
content: Quote from: itdontgo on October 15, 2014, 12:22:25 pmLook closely at the colour of the plating on all the screw terminals, that first one looks like zinc that has been wet.

author: SeanB
author_rank: Super Contributor
timestamp: October 15, 2014, 05:23:32 pm
content: Is it powered by a 12V SLA battery? That commonly will leak acid out of the one connector seal or the other, and this wicks up the wiring and onto the PCB's where it eats the board up and destroys it. Very common on remote receivers and such, as the battery often is less than 5cm of wiring away in the case, and often has large temperature cycles outdoors. Looks like there has been some cooking under the connector as well by the negative terminal.

author: TerraHertz
author_rank: Super Contributor
timestamp: October 16, 2014, 05:58:56 am
content: Mouse pee. Seen it before.

author: Niklas
author_rank: Frequent Contributor
timestamp: October 16, 2014, 07:29:03 am
content: Can you get hold of the wiring that was attached to the terminal? Leakage usually leaves traces. I have seen cables with AdBlue/DEF leakage and the copper strands turn dull black.

author: tautech
author_rank: Super Contributor
timestamp: October 16, 2014, 07:41:59 am
content: Quote from: Niklas on October 16, 2014, 07:29:03 am+1 if the strands are un-tinned copper, they will tell the story...dampness of one kind or another.The insulation may look clean or have been cleaned, but strip some back and all will be revealed.If tinned it will likely look dull not shiny if wetness has been present.

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 16, 2014, 10:00:20 am
content: Quote from: SeanB on October 15, 2014, 05:23:32 pmThis makes sense.CSI eevlog.

author: SeanB
author_rank: Super Contributor
timestamp: October 16, 2014, 05:48:52 pm
content: Centurion gate motor boards................But the nice thing is you can either take the Vector actuator and get a service exchange on it, or just buy the motor itself. Even more impressive is the sealing on the motor itself, it keeps the smoke in totally, even after the motor has cooked itself totally into a charred mess internally. Only was able to smell it after undoing the case screws.

author: timb
author_rank: Super Contributor
timestamp: October 16, 2014, 07:50:19 pm
content: If it's a gate motor board, it could very well be lightning related. We've had a few boards toasted until we put up ground rods every 50ft on the fencing. (Never took a direct hit, just the energy from nearby strikes being picked up into the metal fencing and coupling into the electric gate.)Sent from my Smartphone

author: Riotpack
author_rank: Regular Contributor
timestamp: October 17, 2014, 05:06:06 am
content: Test the PH of the residue?

author: SeanB
author_rank: Super Contributor
timestamp: October 17, 2014, 07:39:24 pm
content: Easy to tell if it was lightning, look for the copper vapour inside the case. That, along with the missing traces on the board is an easy tell.