The computer was moved a few blocks and won't power up now. The 5
volt led comes on but no fans turn on with power switch (including the
cpu fan). Checked the switch, ok. Tried a new (good)
supply, no difference. Tried the cpu in another motherboard,
ok. Does anyone know where I can get a schematic for the
MB? It appears that somewhere I have lost the "power ok" signal
going back to the supply.
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Designed to save the consumer money. One of the items used that cost is saved on, is the Power Supply.
Power Supply is generic, and of low quality. 1) Low quality Electrolytic Capacitors 2) Low quality Power MOSFETs 3) Low quality Rectifier Bridge 4) Too small a gauge of wiring is used
Plus most consumers do not keep the inside of the computer clean, and if they do the Power Supply is usually neglected. The two leading causes of desktop computer failure; the computer is dirty inside, and/or the Power Supply is bad.
With a weak voltage power rail you may see LED's light, and maybe fans spin, but there won't be enough power to turn the Processor on.
[No Processor operating, no computer. No computer = no video signal to the monitor. No Signal, Power Saver Mode, or Sleep Mode is indicated ]
1) If ALL of the LED's were lit up they would use less than 1 Watt of power.
2) EACH fan uses 2 to 3 Watts of power.
3) A typical Processor can use from 51 to 125 Watts of power. Just depends on what Processor it is.
See if there is an unused working computer that has a KNOWN to be good, Compatible power supply; that you can use for a test unit.
Or use a multimeter to test the three main voltages, coming out of the Power Supply 3.3 Volts (DC) [ Orange wires ] 5 Volts (DC) [ Red wires ] 12 Volts (DC) [ Yellow wires ] [ALL Black wires are Ground wires ]
For additional questions please post in a Comment.
OverheatingWhen the CPU overheats then it will shut down (i.e. thermaloverload) and won't boot up again until it has cooled down. If this is theproblem is not fixed then the CPU will eventually fail. A faulty fan causes the problem or the fan and heat sink assembly are cloggedwith dust. Check the CPU fan to see if it spins freely, if not replace the fan. If the fan and heat sink is clogged with dust the remove the dust and make surethe vents are clear and dust free. Use a small brush and can of compressed airto do this.
A bad Power Supply with a weak voltage rail, will produce the symptoms you've just described.
1) IF all of the LED lights were on at once, they would use less than 1 Watt of power.
2) EACH fan uses 2 to 3 Watts of power.
3) A typical Processor can use from 51 to 125 Watts. Just depends on what Processor it is.
You press the Power On button. The first chipset (Integrated Circuit) to receive power is the BIOS chipset. BIOS detects what devices are installed, does a Ram Memory count, turns the Processor on, and hands the computer over to the Operating System. (Windows XP is one example of an O/S)
Have you tested the main voltages of the Power Supply? A) The 3.3 Volt power rail B) The 5 Volt power rail C) The 12 Volt power rail
(12 volt rail must be 11 volts or more. Less = new Power Supply)
It could be an overheating CPU problem.
When the CPU in the computer or laptopoverheats then it will shut down (i.e. thermal overload) and won't boot upagain until it has cooled down. If this is the problem is not fixed then theCPU will eventually fail. A faulty fan causes this problem or the fan and heat sink assembly are cloggedwith dust. Check the CPU fan to see if it spins freely, if not replace the fan.
If the fan and heat sink is clogged withdust the remove the dust and make sure the vents are clear and dust free. Use acan of compressed air to do this.
First remove the power plug from the smps and press the power switch few time and wait for few minutes the re plug the power connector to the smps and switch on the computer if you still dont have power then you will have to check whether the smps work to test that its not enough to test the voltage in the 21/24 pin you will have to short the green wire and the black wire and see whether the smps fan is working if the fan is not working then the problem is with smps
Make sure that the motherboard LED switch on the back panel is set to off and if want to turn
it on go into bios and set it. If it is active thru switch and not thru motherboard bios it will not allow you to turn on PC cause it is in maintenance mode.
It's a bad power supply. Couldn't be a bad Power On switch, because it turns on for 2 seconds.
You have to have Ram to get the computer to function, besides the processor. All you will see is the BIOS Setup screen.
Been using the same power supply?
The power supply has bad Electrolytic Capacitors in it. These bad 'Caps' in turn make a weak voltage rail. You have three main voltage rails inside a computer power supply. The 3.3 volt rail, the 5 volt rail, and the 12 volt rail.
With a weak voltage rail, the processor won't have enough power to run. ALL the lights, (Lamps), use less than 1 Watt. EACH fan uses 2 to 3 Watts. Processors use 55 watts to 125 Watts. Depends on the processor.