Black smoke but cant find damage?

[HobGoblyn]

Hi all, I did a stupid thing, plugged in a cable into the wrong place while my printer was on (plugging in single pin and got the wrong one)

Smoke started to come out and I immediately pulled the cable out (literally started to put it in, saw smoke and pulled it straight out).

Board happily remained on but I turned it straight off , removed board and placed under the microscope.

In the first pic, the yellow circle is where smoke damage was on the board before I cleaned it, and the red arrow is where I saw the smoke appear.

The F3 fuse hasn't blown, the smoke wasn't near R41 etc (but checked them anyway and they're OK)

Second pic shows a more zoomed out pic of the board, and RP1 seems to test similar to RP2, RP3 and RP4.

Common sense tells me if I saw and smelt smoke and had to clean it up, something must have gone, but I can't find it?

Any suggestions?

Thanks

[Manul]

It could be capacitor C3 or something under the heat sink. We dont know what exactly was wrongly connected, description is lacking details.

[HobGoblyn]

The touch screen cable has a single pin for +5v, I plugged this into ground. It's a serial cable

Thinking about it, I probably had the rest of the cable in wrong too.

Underneath the heat sink is a TMC2208 stepper driver

Don't worry, I'll use it as an excuse to upgrade to a better main board.

[fzabkar]

Fuse F3 is resettable (polyswitch or polyfuse).

Part number = nanoSMDC110F

https://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_nanosmdc_datasheet.pdf.pdf

[TheMG]

I've seen resettable (polyfuse) fuses emit a bit of smoke when subjected to a short circuit or large overload, then with the short removed, the fuse reset and worked fine.

They are essentially a special type of PTC thermistor, so they do get quite hot once they trip, sometimes hot enough to burn off any flux or other residue that might be on or under the part.

If the board is working fine I would just use it and not worry about it too much.