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Powering 3 Fans and a dvdrom, is enough to test PSU?

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August 22, 2012 9:44:10 AM

I'll be testing PSU AX corsair 750W by paperclip method. I'm wondering how much load should be there to verfiy that the PSU is good?

The mobo has only power light on when PSU is connected, I think that might be the PSu that is causing issues as I'm not even able to flash the bios with asus USB-flashing-method.

I have ordered a 3-pin fan connector to molex (female) so I can connect the fans directly to the PSU. Should I also add hdd and SDD for max load?
a b B Homebuilt system
August 22, 2012 9:52:59 AM

If you want to test your PSU's rails for voltage stability use one of these

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

There are cheaper versions available for around $15 but they won't show exact values

The only way to test a PSU for load stability will be to test it with the entire PC put together or with an expensive variable load device
a c 122 B Homebuilt system
August 22, 2012 10:43:32 AM

Sounds like new build will not boot.

Work systematically through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.
The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.
http://www.tomshardware.com/forum/261145-31-read-postin...

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. At this point, if you do not have a system (internal case) speaker, you really need one.


Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps, LED's, or fan activity:

Check for line power at the PSU input. Extension cords, power strips, and power cords do fail.

If you have power and no beeps, suspect components in likely order are PSU, motherboard, and CPU.

Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%. The green wire should read 5 volts and drop to around 0 volts when you press the case power switch.


The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
Related resources
August 22, 2012 12:19:45 PM

hi jsc,

I have tried everything that was stated on the thread ""No POST", "system won't boot", and "no video output" checklist” and also what you have listed.
As you also mentioned the symptoms I’m getting are pointing towards components in likely order are PSU, motherboard, and CPU.
I have the power light on, on my ASUS P877z-V deluxe motherboard but that’s pretty much it. I will test with fans as soon as I have received the connector.
But as you mentioned “Running fans and drives and motherboard LED's do not necessarily indicate a good PSU” so not really sure if that will be a good test.
My system did work after the build but turned off during Windows installation and has failed to boot since then. I have tried breadboarding with least components also in a case only mobo, but the error code led display on mobo is not showing any error. Mobo is not even going to asus-bios.usb-flash modus which makes me think that the on/off led on mobo is misleading me and it’s the PSU that is faulty not CPU or mobo as I first thought.
Any tips will be appreciated, I almost got it working and it’s really boring that it stopped that fast 
I also need answer to following:
1. Is there a fuse in PSU? I have corsair AX750W.
2. I have a core i5 processor with factory fan, I have demounted the fan from mobo, do I have to apply the thermal paste again? I can see that the thermal paste has melted on cpu top , so it’s not like before the first use.
3. How to check PSU using digital multimeter?
August 22, 2012 1:34:08 PM

Just noticed that my corsair AX750w 24-pin connector dont have one pin its empty only plastic as seen in the attached photo.



Maybe all the corsair wires are like this as the photo is not of my psu.
a b B Homebuilt system
August 22, 2012 2:34:08 PM

Power8888 said:
Just noticed that my corsair AX750w 24-pin connector dont have one pin its empty only plastic as seen in the attached photo.

http://www.moddiy.com/product_images/d/336/corsair-black-24pin__50431_zoom.jpg

Maybe all the corsair wires are like this as the photo is not of my psu.


Pin 20 on the 20/24 pin connector is not connected, this is by design. It used to be a -5 volt supply for ISA cards but since ISA is obsolete it has been removed.
August 22, 2012 2:41:30 PM

thanks pinhedd :) 
August 22, 2012 3:49:57 PM

Any power supply should supply full voltage(s) under full load at max temperature. To test for anything less is inconclusive.
August 22, 2012 4:17:06 PM

There are two things I did to check, with a multimeter.
You don't need to connect it to the mobo/fans etc for this test.

1) Connect the PSU to mains, power on the PSU. Check the voltage level on the Purple cable. Its the standby 5V. It should be within 5% range.
Without it, your mobo will not switch on the PSU, and the system won't boot.

2) If the above is OK, short the green cable to black. Granted it won't check it under load, but you should hear an audible 'click' to tell you the PSU switched on the power rails. Then measure the voltage on the 12V, 5V and 3.3V outputs.
August 22, 2012 4:17:15 PM

There are two things I did to check, with a multimeter.
You don't need to connect it to the mobo/fans etc for this test.

1) Connect the PSU to mains, power on the PSU. Check the voltage level on the Purple cable. Its the standby 5V. It should be within 5% range.
Without it, your mobo will not switch on the PSU, and the system won't boot.

2) If the above is OK, short the green cable to black. Granted it won't check it under load, but you should hear an audible 'click' to tell you the PSU switched on the power rails. Then measure the voltage on the 12V, 5V and 3.3V outputs.
August 22, 2012 4:19:19 PM

There are two things I did to check, with a multimeter.
You don't need to connect it to the mobo/fans etc for this test.

1) Connect the PSU to mains, power on the PSU. Check the voltage level on the Purple cable. Its the standby 5V. It should be within 5% range.
Without it, your mobo will not switch on the PSU, and the system won't boot.

2) If the above is OK, short the green cable to black. Granted it won't check it under load, but you should hear an audible 'click' to tell you the PSU switched on the power rails. Then measure the voltage on the 12V, 5V and 3.3V outputs.
August 22, 2012 6:10:21 PM

I was all ready to go but then I noticed that my power supply has only black cables, that can happen if you buy a top ranked PSU, how can i paperclip jump start now? are 24-pin standrad and have same cables at same plcae?
I am thinking of getting a diagram and use that as reference
August 22, 2012 7:57:43 PM

proton007 said:
There are two things I did to check, with a multimeter.
You don't need to connect it to the mobo/fans etc for this test.

1) Connect the PSU to mains, power on the PSU. Check the voltage level on the Purple cable. Its the standby 5V. It should be within 5% range.
Without it, your mobo will not switch on the PSU, and the system won't boot.

2) If the above is OK, short the green cable to black. Granted it won't check it under load, but you should hear an audible 'click' to tell you the PSU switched on the power rails. Then measure the voltage on the 12V, 5V and 3.3V outputs.


Test 1 and 2 both successful using an millimeter.
I have also checked all points of 8-pin motherboard connector.
My harddisks also turn on, and dvdrom can be operated (tray open close +light)
That means my PSU is good.
Now I'm down to CPU or Mobo, Iæll start by replacing mobo, I think that will help, crossing my fingers :) 
August 23, 2012 12:45:54 AM

Power8888 said:
Test 1 and 2 both successful using an millimeter.
I have also checked all points of 8-pin motherboard connector.
My harddisks also turn on, and dvdrom can be operated (tray open close +light)
That means my PSU is good.
Now I'm down to CPU or Mobo, Iæll start by replacing mobo, I think that will help, crossing my fingers :) 



Also, there are testing points on the Mobo, they're listed in the manual. Check the voltages there.
!