Imploded electrolytic capacitor

[tonitonitoni]

have seen a lot of buldging caps, but few days ago stumbled upon cap that seemed somehow weird, plastic wraping was undamaged but somehow not right, removing plastic revealed aluminium casing top where vent is bent towards inside. what happened?
dried out too fast?
cap was located in active pa speaker amplifier pcb.

 

[tonitonitoni]

forgot picture sry for double post.

 

[JMFahey]

Probably electrolyte partly boiled and when cooling condensation created partial vacuum and pulled previously weakened top in.

Top is already weakened by stamping so as to provide a safer "break line", hopefully avoiding a catastrophic explosion.
Not always successfully.

 

[Douglas Blake]

Naaa ... that's what happens when you play the music backwards.