Some advice on short circuit

[PeterSpie]

Hello,

I have watched a lot of videos and have some experience in reparing stuff.
But this new to me:
My boss has connected a device with the wrong adaptor. In stead of using 12 volts he connected 48 volts to this device.
I am measuring and there is a dead short between + and ground.
My first suspect is this cap (see picture), because of the different colors. Or is the color of C77 normal?

Should I just remove the cap and do some measurements to see if the sort is gone?
And what about D5, it also looks not that great.
Or is the device not savable anymore.

By the way: the device is a Netgear LB2120 4G router

Regards, Peter

[Grandchuck]

Welcome Peter

I think the diode is more likely to be shorted.

[ledtester]

Concerning color this answer from Quora says:

* Class 1 caps (NP0, C0G ceramics) are usually white. They’re very low capacitance, from below 1pF to tens of pF.
* Class 2 caps (X7R, X5R ceramics) are usually light brown. They’re in the nF .. microfarads range.
* Class 3 caps (Y5V, Z5U ceramics) are usually black or dark brown. Extreme capacitances are possible, but these caps are highly nonlinear and exhibit much lower capacitance at higher voltage.

[PeterSpie]

Thanks ledtester,

learning every day. I Like it.

Regards, Peter

[chilternview]

Post a schematic. We might then be able to speculate what the possible failure mechanisms are - I doubt they're even in this photo.

[PeterSpie]

Hi Grandchuck,

Thanks for your reply.
When I remove it, do I need to replace it? I think it is for protection if you connect the adapter the wrong way?
But, if I need to replace it, how do I know the value? I do'nt have a schematic.
By the way: the device is a Netgear LB2120 4G router.

Regards, Peter

[DavidAlfa]

Inject 12V 500mA current-limited, find the part heating up, replace, done.

[PeterSpie]

Sadly, I don't have a schematic.
The only thing I found was this topic: https://www.eevblog.com/forum/repair/unidentified-switching-regulator-from-netgear-lb2120/msg2976514/#msg2976514

[DavidAlfa]

Those boards are pretty simple, no schematics needed.

[PeterSpie]

But when I find the defect component, how do I know (for example the diode) which diode I need to order?

[DavidAlfa]

That diode seems to provide only reverse polarity protection, not overvoltage, althought I could be wrong.
I say that because I *highly* doubt it would look so unharmed after dumping 48V on it.
Likely the short is either caused by a capacitor or the voltage regulator.

[PeterSpie]

I have removed the diode, and the short is still there.
So, i will continue to look at the capacitors.
The voltage regulator looks ok to me.

[Grandchuck]

Do you have a current limited supply?  If so, DavidAlfa gave good advice.

[DavidAlfa]

Remove the IC, probably that's it.
Very easy to remove, apply some solder so it bridges all the pins, quickly apply the tip to both sides few times and should come off.

[PeterSpie]

Thanks for all the hints!

I don't have a goor power supply jet, but ordered one today.
When I inject the voltage, how can I tell which part is defect|? I don't have a thermal camera. Can I use flux or IPA for this? Put it on and try to see where it "melts" first?

Thanks @DavidAlfa, I will try that also.

Regards, Peter

[kripton2035]

build yourself a shorty-with-display device. it will always serve you to find shorts on a pcb...


http://kripton2035.free.fr/Projects/shorty-display.html

[PeterSpie]

Hello kripton2035,

this makes live so much easier! Great, I would love to buid this.
On your site it says PCB coming soon. Can you tell me when? Or can I buy this "Shorty" complete?

Regards, Peter

[kripton2035]

I began working on the pcb, but got caught on other projects, and now it's been long time and I'm not sure to make a (working) pcb one day...
it's anyway quite easy to build it on a breadboard like I did the prototype. other people did it too.
also it's become so difficult to make and sell small electronic devices from france (or europe) with so many norms, patents, taxes, that I could not sell anything like this on my own. you need a big company and this small $20 device would have to sell at more than $100 to even exist...