19v accidentally applied to 12v PCB/board

[stormy1777]

Friends,
It appears I've accidentally applied 19VDC to a PCB that should only run 12VDC.
The board now does not power on, even with 12VDC..
Using a thermal camera shows entire board remains COLD except one component (near power plug) that heats to 120C and higher!!

Suspected component is marked with "T" (slanted) and "BE", think/hope it is some kind of fuse, in photo just ABOVE the green power terminals and LEFT of the 16V capacitor (on right of photo)

Interesting part is measuring continuity across that component shows 0-reistance and a BEEP, also same thing happens across the green plastic wire power terminals (bottom of photo).. which is not what i'd expect from a FUSE, as it would CUT power and not ALLOW it to flow...

So, now writing/thinking... maybe the allowing of current causes the heating, and that's not a FUSE, but a DIODE that is supposed to BLOCK flow, but it got "blown" and now causes a "short - circuit"...

Now question how to proceed, I have no way to know the exact type/size of Diode.. what if.... I just REMOVE it?? could that cause the circuit to start working again? since it will eliminate the short-circuit and "open up" the board to get power...

I do not know the board vendor or type it is part of a no-name network/switch.

[stormy1777]

Thanks DEAR friend - before seeing your post, could NOT resist the temptation!!

took soldering iron, removed one side came clean, other side did not heat enough i didn't want to harm other component, so it got "ripped" a little, and device is back fully operational.. incredible!!!
thanks... never realized diode acts as a fuse learn something new everyday!!

[stormy1777]

closeup , the heated component is marked "BE" - suspect it is a diode! very tempted to remove entirely, any thoughts welcomed!

[CapLeaker]

Probably a TVS diode that has a certain voltage rating. If it exceeds the voltage it goes short. Yes if you take that diode out, it should work again, just without protection. The code BE is a Vishay SMBG12CA or an SMAJ12A
https://www.mouser.ca/ProductDetail/...2BE8RaAQ%3D%3D

point is: it’s a TVS.

[stormy1777]

Thanks DEAR friend - before seeing your post, could NOT resist the temptation!!

took soldering iron, removed one side came clean, other side did not heat enough i didn't want to harm other component, so it got "ripped" a little, and device is back fully operational.. incredible!!!
thanks... never realized diode acts as a fuse learn something new everyday!!

[CapLeaker]

No. It doesn't act as a fuse. It just shorts out the voltage rail to ground. It is there to protect the circuit from over voltage condition.

[stormy1777]

What is meant they acted similarly, from a FUNCTIONAL point of view (circuit protection), fuse disconnects wire, whereas diode "connected" (short circuit).. always thought only fuse can protect circuit, by cutting power, here, a short-circuit did the trick..

[Agent24]

What is meant they acted similarly, from a FUNCTIONAL point of view (circuit protection), fuse disconnects wire, whereas diode "connected" (short circuit).. always thought only fuse can protect circuit, by cutting power, here, a short-circuit did the trick..

It's not functionally equivalent either.
A fuse is ultimately used to protect against fire, basically. It is not designed to save the circuit. It is designed for your safety.

The diode here is used as what is called an "overvoltage crowbar" and IS a form of circuit protection.
It is not a fuse, and it does not work the same way, nor for the same reasons.

[stormy1777]

Right, I see..

nothing personal really - the quantum continues to interact with itself..

Seems like over-complicating terminology and usage cases, there are many types of fuses and diodes.. sure..
but to claim fuses do not protect a circuit is a bit stretching IMO...

At least wikipedia's first sentence needs re-written:

https://en.wikipedia.org/wiki/Fuse_(electrical)

"...operates to provide overcurrent protection of an electrical circuit"

Same mistakes are carried over to AI-overview:





In an era when even definition of Bread (soft sponge sold in plastic bags) is not clear, possibly electrical components or other elements are not clear

As some say...if you can't convince them, confuse them

Suggest to close this thread and let each continue their path of (self) discovery and should they choose to pursue grammar or other philosophical or electrical journeys to continue in other more focused/dedicated threads (from reading, seems like that's a long-running debate, on the "exact" definition of "bread" or "fuse" (protect wire or circuit, etc.)

do good.

[Agent24]

Right, I see..

nothing personal really - the quantum continues to interact with itself..

Seems like over-complicating terminology and usage cases, there are many types of fuses and diodes.. sure..
but to claim fuses do not protect a circuit is a bit stretching IMO...

Okay sure, yes, they do protect a circuit, technically, but ultimately, why? As you said, over current... What is the resulting effect of over current?

(Hint: things getting too hot... which leads to burning... Which leads to fire)