Electrical short caused buzzer/speaker cable to melt?

[i386dx]

My chassis has a front panel buzzer, it's not a true speaker - just connects to the beeper on the motherboard.

Last night it melted, seemingly out of nowhere. Turned the PC on and smoke started pouring out. The only explanation I can come up with is that the buzzer cable was routed behind the motherboard tray, and was somewhat pinched by the chassis panel; it's possible that it had frayed and deteriorated each time I'd removed the side panel which degraded the insulation and potentially exposed copper.

I'm not really sure how a short on a 3.3v header can cause the wire to overheat like this.

This is the only possible explanation I can come up with. Anybody else care to chime in? This was the only symptom, the PC continues to work fine. Thanks.

 

[Hotwired]

The voltage is enough, modern torches use 3V leds and lithium batteries easily push 3A+ through them which causes a fair bit of warming.

Looks like the positive wire insulation roasted off but not the black wire so I'm guessing it didn't short the header across itself but shorted the + into the metal case which may have bypassed usual current limitation on the header? Or maybe a tweeter header always did have enough current to melt insulation if shorted.

 

[i386dx]

The voltage is enough, modern torches use 3V leds and lithium batteries easily push 3A+ through them which causes a fair bit of warming.

Looks like the positive wire insulation roasted off but not the black wire so I'm guessing it didn't short the header across itself but shorted the + into the metal case which may have bypassed usual current limitation on the header? Or maybe a tweeter header always did have enough current to melt insulation if shorted.

Thanks. Really appreciate this. Fair shout abou the 3V LED torches, I guess the 3.3V really was enough for the meltdown, especially in the event of a short where the current was allowed to do its thing.

I think it must be a short because that header is only normally powered for a split second when it is beeping. The magic smoke happened just after the computer came on, I don't think there was a POST beep, just fire.

The other thing I can't rule out is a goofy motherboard; this is a Socket 370 build from 1999; so there's that. I may test it with one of those basic motherboard buzzers you get free with PC cases, I have plenty of them hanging around. If they start burning in the absence of an obvious frayed cable, then it's time to retire the board.