Short to ground fixed, but what is the component I removed responsible for?

[Freqhog]

Hello everyone,

I have been watching EEVBlog on YouTube for years now and always enjoyed the content, even though I really don't understand much about electronics. I've always had a fascination with electronics, but I really lack the knowledge. The only work I've done was replace the through-hole capacitors in my flat screen TV to get it working again.

I have a laptop which developed a short to ground fault about a year ago. I never bothered looking into it because I thought it would be too much for me take on, but I got curious to see if I could do anything. After many YouTube videos and testing with a multimeter later, I miraculously discovered the cause. It was a defective surface mount capacitor. I removed the capacitor from the circuit and now the laptop works again! It find it crazy that such a tiny, inconspicuous component can be responsible for preventing an entire device from operating.

I feel so proud of myself for finding the issue and seeing the computer boot again, but I have to wonder, what exactly was this component doing? I don't see any anything wrong with the computer now that the part removed. Do I even need to bother replacing it?

The computer is a Dell Latitude e7440 laptop and the failing component was the "PC10" capacitor which was placed between GND and +DC_IN_SS

If it turns out that I have to replace it, could I please get some help in locating a suitable replacement to order online?

Thank you all for listening.

[bdunham7]

Probably just a noise filter.  Post some photos, a picture is worth 1000 words.  Those of us that fix stuff like that work mostly by looking at it, schematics and parts lists are hard to come by.

[atmfjstc]

Can't know for sure without the schematic, but it is almost certainly a bypass capacitor. You can find more details online, but basically, bypass caps are used for filtering noise and working around non-ideal behavior of power supplies. Intuitively, when placed between ground and the positive voltage supply they help ensure that the voltage supply remains a constant +5V or whatever, regardless of what the chips are doing.

In most cases bypass caps are not critical - the device will still function but will be less stable, more vulnerable to EM interference, and will cause more EM interference itself. ISTR our esteemed host himself made a video where he muntzed away all the bypass caps in an 8-bit computer and it still seemed to work, at least for a few minutes on video.

I'd stiill replace the cap, just to ensure maximum stability from the laptop.

LE: Some great info from the man himself:

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[Freqhog]

Thanks for the replies everyone.

Here is a photo with the part I removed: https://imgur.com/a/QakZpui

Where can I buy a replacement? I tried looking on digikey, but I don't understand exactly what voltage/farad I should be looking for.

[alsetalokin4017]

I'd recommend testing the old one that you removed to see if it really is shorted. It would be more common for such a capacitor to fail open rather than shorted. It is possible that you removed a solder bridge or bit of contamination that caused the short when you removed the capacitor. You might get lucky and be able to reuse the old cap now that the short is removed. Maybe.

To replace a single cap like that I'd scavenge one from an old motherboard or other defunct device. The value isn't going to be too critical, but 100 nF is a typical value for bypass.

[CJay]

I'd recommend testing the old one that you removed to see if it really is shorted. It would be more common for such a capacitor to fail open rather than shorted. It is possible that you removed a solder bridge or bit of contamination that caused the short when you removed the capacitor. You might get lucky and be able to reuse the old cap now that the short is removed. Maybe.

To replace a single cap like that I'd scavenge one from an old motherboard or other defunct device. The value isn't going to be too critical, but 100 nF is a typical value for bypass.

Not my experience, the majority of MLCC capacitor faults on power rails I've bumped into have been either leaky or shorted (leaky may be a precursor to short)

[MLXXXp]

It would be more common for such a capacitor to fail open rather than shorted.

I just finished replacing a MLCC that had failed "leaky". Before removing it, I noticed a very small chip taken out of the corner. It might have been damaged by knocking the soldered circuit board against something during assembly. Once removed, the MLCC measured fine, so it could have been under stress while soldered to the board, making the problem disappear once that stress was relieved.

https://www.murata.com/en-global/support/faqs/products/capacitor/ceramiccapacitor/mnt/0007