Found a blown cap that looked totally fine from the top

Was working on a 10 year old Samsung TV from a customer in Portland. No picture but sound worked. Pulled the board and saw nothing obvious. No bulging tops on any caps. Decided to desolder one anyway just to check. Sure enough the bottom was corroded and leaking brown stuff. This was on a power supply board, main filter cap. Never seen one where the damage was all underneath. Now I desolder suspicious caps from boards even if they look good. Learned this trick from a forum post back in 2018. Has anyone else found hidden cap damage like this before?

3 comments

3 Comments

emma_lee2212h ago

Yeah, the whole 'looks fine from the top' thing is real. I've pulled caps off a monitor once that looked pristine on top but the bottom pads were completely corroded away. Your mileage may vary but I've started just checking ESR on anything over 5 years old, it catches those hidden failures before you even desolder.

samreed10h ago

Right there with you, @emma_lee22. ESR meters are a lifesaver for that exact reason.

william_craig79h agoMost Upvoted

emma_lee22 said "looks fine from the top" and that hits the nail on the head. Here's what gets me though - people always blame heat for blowing caps but I seen corrosion do just as much damage. Those leaky caps drip electrolyte down onto the board and it eats the traces underneath without you ever knowing. That brown stuff is basically acid. I pulled a cap off a power supply once where the leg had completely dissolved inside the hole. You could wiggle the cap side to side and the leg just snapped off clean. The top looked perfect but there was nothing left below. It's like a hidden time bomb. If you ever see that brown gunk on any cap even if its dry just bin the whole board because the damage is probably already done.