Power supply problem?

[Sheeze]

Whenever I unplug and move my tower (like from home to school) and set it up again, the computer doesn't start up when I try to turn it on. I press the power button and nothing happens. I usually have to unplug and replug the power cable and flip the power switch on the back of the case several times before I get the computer to finally start up. Lately, though, I've been having more problems starting up, and I haven't even moved my computer around. I press the power button and for a second the computer seems to be starting up and then nothing happens. I have to press the button a second time for it to start up. Also, sometimes it does start up but the monitor doesn't display anything, and I have to press the reset button on the tower. All this leads me to think that something's wrong with my power supply, but I'm not sure.

Any help would be appreciated. Thanks.

[Paul T]

check all conections, mine did the same, power cable wasn't in right

[Sheeze]

I have, they're all in tight.

[Paul T]

wot about the inside?

[Sheeze]

Yeah, I looked inside my case the other day and everything was fine.

[John0904]

I would have to say it is the PSU causing problems by the description you gave.
Even with the power switch off, the PSU still has power. Very minimal power, mind you.
Which is why when adding or removing PCI/AGP cards, the power cord has to be unplugged from the computer.

Eventually with repeated plugging in and out of the wall socket, the brushes get worn down. (Pretty sure that a PSU has brushes. If not, someone will correct me. :) )

Eventually, the motor will surge then quit or just quit.
You don't want a PSU to surge. :) Things will probably be worse at that point.

[Sheeze]

So should I replace it now?

[John0904]

Given the same situation, I would.
Why wait for a potential meltdown? :)

[Sylvander]

Download a copy of my diagnostic flowcharts from here
www.erniek.eclipse.co.uk/downloads/sylvanderdiags.zip
and print them to leaf through.
Begin on the STARTUP chart.
These may help you analyse/understand the symptoms and their likely causes.

"the computer doesn't start up when I try to turn it on. I press the power button and nothing happens"
Sounds like the PC is "Dead". Are there no signs of life whatever?

"flip the power switch on the back of the case several times before I get the computer to finally start up"
That's probably a significant clue. Not sure what it means though. Perhaps that resets the PSU?

"I press the power button and for a second the computer seems to be starting up and then nothing happens"
Another significant clue. Sounds like the PSU is enabled; powers up, but a problem is detected [by the CPU? which switches the PSU off to protect the hardware?] Is the demand too great for the PSU to supply? Is there a short in the hardware?

"sometimes it does start up but the monitor doesn't display anything"
That's a failure to complete the POST. The video card is only enabled if the POST completes.
QUOTE
"The BIOS performs the power-on self test (POST). If there are any fatal errors, the boot process stops."

Here's the greater quote:
"System Boot Sequence
The system BIOS is what starts the computer running when you turn it on. The following are the steps that a typical boot sequence involves. Of course this will vary by the manufacturer of your hardware, BIOS, etc., and especially by what peripherals you have in the PC. Here is what generally happens when you turn on your system power:
1. The internal power supply turns on and initializes. The power supply takes some time until it can generate reliable power for the rest of the computer, and having it turn on prematurely could potentially lead to damage. Therefore, the chipset will generate a reset signal to the processor (the same as if you held the reset button down for a while on your case) until it receives the Power Good signal from the power supply.
2. When the reset button is released, the processor will be ready to start executing. When the processor first starts up, it is suffering from amnesia; there is nothing at all in the memory to execute. Of course processor makers know this will happen, so they pre-program the processor to always look at the same place in the system BIOS ROM for the start of the BIOS boot program. This is normally location FFFF0h, right at the end of the system memory. They put it there so that the size of the ROM can be changed without creating compatibility problems. Since there are only 16 bytes left from there to the end of conventional memory, this location just contains a "jump" instruction telling the processor where to go to find the real BIOS startup program.
3. The BIOS performs the power-on self test (POST). If there are any fatal errors, the boot process stops. POST beep codes can be found in this area of the Troubleshooting Expert.
4. The BIOS looks for the video card. In particular, it looks for the video card's built in BIOS program and runs it. This BIOS is normally found at location C000h in memory. The system BIOS executes the video card BIOS, which initializes the video card. Most modern cards will display information on the screen about the video card. (This is why on a modern PC you usually see something on the screen about the video card before you see the messages from the system BIOS itself)."

Perhaps you should try reseating your RAM. The BIOS Setup may be configured to "shadow" the BIOS to RAM, and if that RAM is faulty, then the BIOS will be rather unreliable. All these problems are happening whilst the BIOS is in control.

You could swap in a known good PSU to see if that makes any difference.
A "Bare-Bones Boot" would be a good idea.

[Fruss Tray Ted]

[quote](Pretty sure that a PSU has brushes. If not, someone will correct me. :) )
And that would be me. :p

Brushes are for only some electric motors such as A/C driven ones in your vacuum cleaner or a car starter. The power supply uses transformers to convert to the correct voltage and rectifiers to convert to D/C (direct current that will flow in one direction only). This is all done with 'inductance' and no physical connection from one to the other besides a common ground in some instances. The fans scattered throughout a pc and in power supplies also are driven by inductance motors which have no brushes either. Otherwise they would not last near as long as they do these days.

Now if you had said 'contacts', such as what a solenoid would have, that would be a different story altogether. I am not aware if there is any in a PSU but this gives me a project to find out the next time I find a defective one (more things on the to-dew list :rolleyes: ).

Also when you shut (boot) down your pc, there is still power to the motherboard from the PSU. When you flip the switch on the back of the PSU, you have shut it off and there is no power going to the motherboard as evidenced in that some boards have an LED on the board itself and when you flip the switch off, out goes the light. Removing the cord is more for PSU's that don't have a switch and for general insurance.

Some people insist on leaving the PSU connected in belief that this is a way of grounding everything to prevent 'memory module killing' static discharges. I don't leave the pc plugged in when assembling butI have not heard of any problems the other way either, so to each his own.
_____________________

Back to the poster's problem.
Yes, it seems it is the power supply that is at fault but that is not a definite yet. By the fact that the pc tries and fails to start at times is another hint. It is possibly heat, the power good sensor isn't happy for some reason and possible bad connections as well.

Open the left side of the case and clean out ALL dust with a can of compressed air. Then, with the case still open, try to boot. Does the CPU fan spin immediately upon pressing the switch? Just to rule out bad/dirty connections, I would break and make as many contacts as possible. Disconnect all plugs from their sockets a couple times each to 'clean' or refresh connections. The contacts corrode over time and lose the ability to conduct electricity from plug to sockets occasionally so this is the easiest and least expensive thing to try first.

When you remove and replace your RAM, be sure to have your forearms touching the side of the case or use a wrist strap.

If refreshing all connections doesn't help, then we'll need to move to the next step which would be to try another PSU in your pc.

[mario]

I had a similar case with a Compaq 5170 with an uncertain PSU functioning (power on only by repeating it many times) untill one day it definitely refused to power on any more. I decide PSU was dead and bought another to substitute it. So opened the case and dismointed it disconnetting of course all connections to mobo and devices. Then I discovered the new one was a different size (bigger) then the original in the Compaq.
So I re-mounted the "dead" PSU and, just in case, made a last attempt to power it on.
For some unexplainable reason the PSU started working as it was new and still (after a coulple of years) is. So probably disconnectin it completely and cleaning it has resolved for some misterious reasons the cause of malfunctioning