Power Supply Question???

[1966]

I am currently ussing a Antec 350 watt power supply that has just started doing something goofy. When I go to shut the computer down thru Windows it will shut down and then in a few minutes you can see the blue diode come on with the fan and then it stops and then it starts up again. If I leave the computer on for a longer period of time then it shuts down normally without any problem. I am suspecting the power supply itself as the problem but a capacitor in the power supply causing the main problem. I can start it up anytime as normal. Does not create any problem while its on. Acts like it just can't stop itself, but never enough power to actually restart the machine. Looking for comments and suggestions...

[1966]

Will try to help this along as I look for an answer, but IF I swap out my current supply with another just to see what will happen and it does the same thing then am I not looking at a shut down problem verses a power supply problem?

[mjc]

Will try to help this along as I look for an answer, but IF I swap out my current supply with another just to see what will happen and it does the same thing then am I not looking at a shut down problem verses a power supply problem?

Right...

But you could be looking at something else...like a sticky power switch on the machine, too. I know you said you are using Windows to do the shutdown, but if the switch is nearly all the way open, barely making contact, then it might be enough to at least start it (or attempt to until the drive vibration jars it all the way open--been there, done that).

One way to eliminate the switch is to pull the lead from the header, use something (a small screwdriver, your wet finger...anything conductive) to short the header pins to start the machine, then go through Windows shutdown. If it doesn't restart when the switch is out fo the loop, then the problem is probably the switch...if it does, then do the power supply swap.

[kiosk]

I've run into similar problems twice:

Computer #1: when I try to shut down, disks spin down and everything, monitor goes off and the power supply then starts cycling on and off about 10 times per second, causing the system to rattle loudly (mostly fans and floppy disk drives starting up and "tugging"). I must pull the power cord to stop this. This was traced back to the failing mainboard capacitors (as the problem happened with this mainboard only, tried numerous others and none exhibited this behavior).

Computer #2: When I plug in the power cord, system starts up immediately, without waiting for me to press the power button. Otherwise acts normally. This was tracked down to the mainboard, um, "feature" :D , as no other systems did this when connected to the PSU.

I don't know. If I were in your place, I'd suspect the mainboard. But then again, it's much easier to just swap out the PSU in order to check whether it's the one component that's causing the fault.

[1966]

Well, I thought I knew where the problem was and I was correct, its the power supply. I will give a brief run down of what I did to determine my problem child. First, as mjc has suggested I removed the power on switch lead from the motherboard. With the power on switch out of the picture, the computer had already been shut down thru Windows. In approximately 10 seconds or so the blue led and fan start running again. I unplug the ac and all qiuet again. Second step for me was to unplug the power supply lead to the motherboard and re- apply the power thru the ac cord to computer. Its was all quite for a few minutes when I then heard a very high frequency squeal coming from the supply. I am guessing that its the filter capacitor but wont know until we open the supply and check it. I replaced my Antec smartblue 350 watt supply with a supply I had ungraded to before I had this motherboard, a Power and PC Cooling 275 watt silencer unit and operation normal. Thought this might help others who experience similar problems with their computers and a warning with this. If you have no prior electronic experience and not sure what your doing, stay out of the supply, you could get a very nasty surprise.