A Puff of Smoke and All is Well

[Grandcheapskate]

Hi Guys,
I have a P90 computer I do not use very often. The other day I went to boot it up and it went on for about a second and then off. I tried a couple more times with the same result.
Today I took the cover off and unplugged the power supply from the motherboard and the machine stayed on (CPU fan spun) so I figured the power supply was not shorting out. I reconnected the power supply and again the machine only stayed on for a second. Figuring it may be one of the devices I removed the power from the hard drive and booted the machine.
Here's where it gets weird. There was a puff of smoke and a sound like escaping air. But the machine stayed on and got to the point where it asked for a boot disk. I shut the machine down and reconnected the hard drive. I rebooted the machine and everything is working.
I have not checked over the motherboard but my guess is it blew a capacitor. Maybe disconnecting the hard drive allowed enough power to flow to a bad capacitor.
Are there situations where a capacitor can blow and yet the machine continues to work?

Thanks...Joe

 

[Chuck(G)]

Happens a lot with tantalum caps, but they usually just go "bang" like a squib. Check the Rifa film caps in the power supply AC filters--those can smoke a lot. Inspect electrolytic caps for "doming" or leakage--when they go, you'll get that "whistle".

 

[Unknown_K]

The other nite I heard a loud bang and the video on my LCD went blank. I figured crap I blew my video card in my main machine, but it was still running but the KVM lights were off.

Ends up a 470uf 25V thru hole capacitor exploded in the power brick to my KVM. Installed a spare and everything works again. Never seen that before.

 

[daver2]

A partially shorted tantalum bead capacitor could cause a current overload with the result that the power supply shuts down before it goes bang.

Removing the drive will cause the excess current to flow in the faulty capacitor. It still may not go bang, but (in your case) it looks like it burnt it sufficiently well to cause it to go open circuit.

Hunt it down and replace it...

Dave

 

[Grandcheapskate]

Thanks guys. I looked at the MB and I do not see any caps with mushroomed tops so if there is a blow/damaged capacitor it must be inside the power supply. I'll have to remove a couple CD drives to get at it. I kept the machine running yesterday for about an hour and there were no other signs of trouble.

Thanks...Joe

 

[modem7]

Regarding the "Rifa" that Chuck referred to. That is an informal name. See the 'Line Suppression Capacitor' section at [here]. The crack in those is normally along the side. In that section is a link to a photo of a failed WIMA made capacitor, and from that, it can be seen that sometimes the crack is relatively small, hidden if the capacitor is up close to some other component.