[bake]

I have a dell 2400 pc. The unit will not power on. No fans or exterior lights come on. Opening the case I found a green light on the mother board illuminated. Test with a digital meter on the power plug on the board showed 5v on two pins. All others showed nothing. How would I determine if the power supply or motherboard is faulty. Thanks for any help.

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In a word, subsitution, but Dell uses proprietary power supplies, so it isn't that easy. Disconnect everthing but the mother board and hard drive and see what happens.

[Tyger]

In a word, subsitution, but Dell uses proprietary power supplies, so it isn't that easy. Disconnect everthing but the mother board and hard drive and see what happens.

[Doby]

There may be another way, remove the psu from the computer plug into wall outlet then on the 20 pin connector use a paperclip and short the green and any black wirer.

This should turn the psu on if it don't then its bad, if it does turn on it still could be bad but we can check the rails with a volt meter.

Understand I don't have a dell psu in front of me but the color coding on the wirers is always the same even with brand units at least all that I have seen/tested.

Rick

[bake]

Thanks guys,

Tyger, No change with everything dissconected.

Rick, Jumped the green wire to a black. Fans,lights and monitor came on. Did not boot.

[Doby]

My test was not meant to boot the computer it was only to test for a dead psu and I did say to remove the psu from the computer. I hope I was clear enough.

You should not short the wirers of a psu if its still connected to the mob
Please be more carefull when following instructions

Rick, Jumped the green wire to a black. Fans,lights and monitor came on. Did not boot.

What do you mean the monitor came on? Did the dell logo appear?

If so,

That tells me the psu is good, disconnect all power connections from all drives.
You now want to try and boot into bios so power on and when the dell logo appears tap the F10 Key and try and enter bios.

[bake]

My mistake, I did jump it while on the board. Seems that nothing has changed with jumper removed. Hopefully I didn't make my problem worse. The dell logo did not come up. Hard drive and disc drive unplugged, still dead except for the green light on the mother board.

[mrdrphil007]

I had the same problem with a PC I built. The power supply was dead. I ordered a new one, problem solved. fwiw

[Doby]

Ok, now we should test the psu, remove it from the computer completely.

The psu needs some sort of load put on it, I normally plug a hard drive and cd drive into it to accomplish this but if you do make sure you disconnect the ide cables that connect the drives to the mobo

Short the green and any black wirer to turn the psu on, then using the volt meter test any red wirer on the 20 pin connector by touching the meters + probe to the red wirer and the meters - to any black wirer.

Post the reading.

Now do the same with the yellow,orange and gray.

Note the gray wirer is very low voltage it is the power good signal to the board and can be as low as .5v so be carefull when you read the meter but this wirer must have some voltage.

This test will tell if the psu is producing enough voltage to power on the computer.

Rick

Rick

[bake]

Rick, measured the voltages per your instructions. Readings listed below

Red- 5.02v
yellow- 11.80v
orange- 3.41v
grey- 5v

[Doby]

The power supply should be ok the voltages are normal.

Is there a case speaker connected to the system and are there any beeps?

Try the ram in another slot but if there is a case speaker connected it will beep if the system could not find usable memory but its worth a shot.

If trying the ram in another slot does not work disconnect all drives and remove all cards except the video then try and boot if the dell logo appears then its one of the drives or cards if it does not it could be the mobo or the cpu.

If the above does not work we can try and determine if its the mobo or cpu next.

Rick

Edited by Doby, 08 October 2005 - 08:31 PM.

[bake]

Rick,

There is no case speaker so I hear no beeps.

Memory in the other slot, still dead except for green light on board.

Modem out and all drives disconnected from Pwr supply and board, No change. Still dead except for the green light.

Also, I tried the modem in a working machine and it would not boot. So I am thinking this one took a hit and the problem is likely the board. Possible? Thanks,

Lee

[Doby]

Well Lee it sounds like its the mobo or cpu, look the mobo over very carefully look for bulged or leaking capacitors although some times there is no visible signs of damage.

Make sure the cpu fan is connected to the mobo, when you try and power on does it spin or try to spin even for a second?

Look on the mobo for the "cmos" header and make sure it has a jumper on it covering pins 1&2, if this jumper somehow came lose or is not present it could cause the problem.

If none of the above pull the cpu out and look it over for any sign of burn marks or burnt edges.

Rick

[Doby]

I just had another thought because of something you did eailer, remember when you jumped the green and black wirer on the psu while it was connected to the mobo (anyone reading along don't do that it was a mistake and not a recommended proceedure) and the fans turned on.

Could it be the power switch because that made the board power up. So with minimal components installed cpu with fan and heat sink, ram, psu and video card trace the wirers from the case switch back to were they plug into the board and disconnect these wirers. Then with a screw driver touch the two pins the wirers connect to. This could start the computer, see if the dell logo appears.

I am unsure if this can be done on a dell because on some brand computers the power switch is grouped together with many other wirers to a connection on the mobo but have a look and see.

Rick

[bake]

Hi Rick, I don't see anything on the mobo or the processor that shows signs of damage. Jumping the pins for the power switch did nothing either. I think I will go ahead and price a new mobo and processor to see if it is worth replacing them. Thanks very much for the help you have given me.

Lee

[Doby]

Your welcome, sorry it didn't work out, my guess bad mobo, cpu problably good.

Rick