Appreciation post: The guy who taught me to check capacitors with my thumb

Some dude on a forum years back said if a cap feels warm to the touch before you even power it on, it's already dead. I laughed it off until I found a swollen 470uf in a monitor that was only 3 months old, warm as a coffee cup. Has anyone else got a weird trick that actually works every time?

2 comments

2 Comments

the_ryan14d ago

I get where you're coming from and the warm thumb trick does work most of the time, but I actually see it a little different. A lot of caps run warm just from being in a tight spot next to a hot chip or power transistor, so warm doesn't always mean dead. I've pulled caps that were absolutely cool to the touch but dead on a meter, especially in cheap power supplies where they just fail open with no swelling or heat. The real tells for me are bulging tops or any brown crusty stuff leaking from the bottom, that's a sure sign no matter what the temp is. So yeah, warm is a decent heads up but I wouldn't bet a repair on it alone. Do you ever check ESR on caps that look and feel fine but act weird in circuit?

lily_singh214d agoMost Upvoted

Warm cap" trick works. Press your thumb gently on smaller caps too, they bulge before swelling. You ever pop one off?