Spent 4 hours chasing a phantom short on a laptop motherboard

Had a Dell Latitude come in that wouldn't power on at all. Found a short on the 3.3V rail, so I started pulling components. After checking every cap and chip for hours with my thermal camera and multimeter, the short was still there. Turns out the tiny metal shield for the WiFi card was bent and touching a capacitor leg right under it. I only saw it when I took the whole board out of the frame at a different angle. Straightened the shield with tweezers and it booted right up. Anyone else had a simple mechanical issue hide an electrical fault like that?

3 comments

3 Comments

willow_martin3mo ago

Yeah, that "tiny metal shield" thing is a classic. Read a forum post once where a guy spent a week on a desktop that wouldn't post, and it was just a loose standoff touching the back of the board.

abby_chen1mo ago

oh i gotta disagree a little with the_julia's take there lol. that's actually the other way around - it's a mechanical issue causing an electrical fault. the shield bent and physically touched a cap leg, which made the electrical short. same thing with those loose standoffs, they're physical objects touching where they shouldnt be. the root cause is mechanical, the symptom is electrical. had a ThinkPad once where a screw fell out and rolled under the board, same deal - physical thing creating a short that looked like a dead component. little stuff like that is what makes board repair so frustrating sometimes haha.

the_julia3mo ago

That's an electrical fault causing a mechanical issue, actually.