PC no power being sent

[msa969]

I am getting a problem with some of the computers in the labatory.

The problem is that two computers don't seem to start. That is no power being transimitted to the computer and as a result the PC does not turn on.

It is strange because the PC has been working fine and all of a sudden the power goes and nothing happens.

What can be the problem????

[deddard]

Could you just clarify things a bit?
When you say there is no power being transmitted to the PCs, do you mean that there is no voltage reading at any point within the PC, or just that when you try to boot, nothing happens?

A couple of things to check if there is no power - nothing comes on when you hit the switch:

Is the power cable plugged into the mains (sounds simple, but unless you are the only one there, someone could have unplugged it)
Is the power switch on the BACK of the PC switched on (there should be a rocker-switch on the PSU)
Can you successfully switch on the monitor (I don't mean get a signal, just get the 'on' light to come on)

[Paleo Pete]

Could be bad power supplies, lightning and power surges can damage power supplies quickly and with no warning...

Also check for Bad Capacitors (http://www.pcguide.com/vb/showthread.php?s=&threadid=25482). I see lots of those lately, and most make the computer suddenly refuse to power up for no apparent reason...a lot act really strange too...

[msa969]

deddard:
-do you mean that there is no voltage reading at any point within the PC?

Yes no power (i.e. voltage) being transimitted at any point during the boot as a result the PC does not boot.

I have checked the power cable.
Power switch on the BACK of the PC atached to the PSU is switched on (i.e. set to 1 as opposed to 0)

Paleo Pete:
I read with interest the articles on capacitors and contribution from pentachris et al. and I was dead cert this was the problem. When I opened the PC there was no bubbling, leaking or spillage i.e. telltale signs of CAP problems, so I changed the PSU and the PC is working.

I am still a little concerned since over the past year I have changed over 6 power boxes, this as you can imagine is unnecessary cost and bother.

I have also invested in surge cables but still seem to get the sudden unexpected problem with PC not wanting to boot, What can be the problem??????

I have a question regarding surge cables, at one area I have plugged a surge-extension cable to the wall socket and because at present I do not have enough surge cables to go round I have attached normal extension cables to the surge-cable and then attached the PC, is this OK???? I assume this should not be a problem????

[Budfred]

If you mean surge protectors, it is probably a problem. I use a Uninterruptible Power Supply (UPS) which provides true surge protection. Most surge protectors do little or nothing. If you don't use a UPS, then at least get a surge protector that comes with a substantial guarantee for equipment damage since it may be a little more likely to be useful.

Also, what power supplies are you using? If you are using low wattage or cheap ones, they may simply be overwhelmed by the system....

[ski]

How many computers are connected to a single surge arrestor?

Did the power supplies start failing on computers connected as above, or did they also fail on computers connected to their own surge arrestor(one computer to one arrestor)?

[msa969]

Budfred:
-I use a Uninterruptible Power Supply (UPS) which provides true surge protection

I have an UPS but at present it is only being used as an emergency power supply i.e. if and when there is a power disruption.

-If you mean surge protectors

Yes I mean surge-protectors.

ski:
How many computers are connected to a single surge arrestor?

About 3 (note my surge-protector is like a glorified extension lead with 4 sockets for 4 plugs)

-Did the power supplies start failing on computers connected as above

Yes it failed once with me with the surge-protectors (I can't be hundred percent sure with the other times since previous failures weren't logged, but I think even this failures happened with surge-protectors.)

[mjc]

Are you, by any chance, daisy chaining power strips?

Also, you should no have more than on computer plugged into one power strip. They can be overloaded, too.

[deddard]

In electronics, the correct way to test where a fault is is the half-split method. in a PC this would be something like:

Is the computer booting?
Yes - nothing to worry about, but that's not why we're here!
No - do the obvious thing, and check that all connectors are seated correctly, that all switches that should be on are on.

Does this solve the problem?
Yes - it was a switch or connector fault.
No - time to test the half -way point. On A PC, the easiest place to do this is outside the PSU - in other words, the end of the power cable that connects to the PC.
To test this, I don't advise sticking a voltmeter into the lead socket, but just unplugging it from the PC and plugging it into your monitor. Switch the monitor on - does the 'power on' LED light up?
Yes - the fault does not lie on the 'mains' side of the power supply.
No - the fault lies on the 'mains' side of the power supply - change the fuse and retest. If this is unsuccessful, change the lead and retest.
If this is unsuccessful, then the fault lies in the mains socket, whether that is an extension or otherwise. You'll need to trace things back to the mains if you are using extension leads.

If the monitor does indicate power is coming on, then the fault lies within the PC. The next stage is to find the next half-way point.

Plug the cable back into the PC.
With a voltmeter, test one of the power connectors - a 12V rail should show (no surprises) around 12V.
Is the correct voltage showing on the power connector?
Yes - the problem is not a simple fault with the PSU (more later!)
No - the fault is either the PSU, or a short-circuit within the case.

If there is no voltage reading, then the next stage is to unplug all of the power connectors from the motherboard, hdds, cds etc. then retest the power connector for the correct voltage.
Is the voltage correct?
Yes - there is a short circuit on the motherboard or other devices within the case.
No - the PSU is not working.
If the PSU is not functioning, then the obvious solution is to replace it, unless it has replaceable fuses, in which case these should be replaced, and the psu retested.

If the voltage reading is present when no connections are being made to the motherboard etc, then you need to carefully look around for short circuits - power connectors should be checked to see if there are pins bent or touching metal of any kind, this includes the power connectors (molex) and the motherboard/hdds themselves.
The motherboard should be checked, look for loose screws etc, or anywhere the +V rail could be shorting to earth.

If you find a problem, take the corrective steps, connect everything up, and boot the machine.

[deddard]

Another possibility is the UPS.
They have limited power, so test the PC without using the UPS - if this solves the problem, then the UPS simply can't handle the pressure.
Another thing, as has been pointed out above, is the problem with daisy-chaining extension leads. everything has a limitation, and putting more than one of these together can cause problems

[msa969]

deddard:

Thanks for the detailed steps to follow.

Please not the UPS at present is only being used on the SERVER as back up to any power failure i.e. if and when there is a power disruption.

Please not also after replacing the computer that want start I replaced it a new PSU and the computer worked okay and at present is still continuing to do so.

I checked the replaced PSU that was in the computer with a simple test-pen and to my amaze amount it was showing electric power was being sent, that is the diode in my test-pen was shining bright red.

I don't have a voltage-meter at present to test if the wires are sending the correct volts i.e. (I think 12V and 15V?). I guess I should do this as well??

mjc

I have more than one computer on a power strip. At present this is because that are limited wall power sockets so I have needed to use extension leads.

[ski]

The PS should be tested with a voltmeter while it's connected to the system and while the system is powered up in order to get accurate readings(except for the 3.3 volt leg I believe).
Yellow and black wire: +12V
Red and black wire: +5V
Orange and black wire: +3.3V

[Budfred]

If you have multiple computers on power strips and daisy chained power strips, you are asking for big repair and replacement bills...