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2 Bronze

Precision t7400, No response to power button.

Hey all.

I just picked up a friends Precision t7400 machine and are running into a bit of a wall my, admittedly slim, skill with hardware can't really work with.

When I press the power button on the front of the machine nothing happens. No lights, no sounds, no response what so ever...

I have tested the power supply via the small button on the rear of the tower, and it lights up solid green and all the fans, the dvd-drive and the hard disk turn on. The small hard disk icon on the front of the machine also lights up.
The yellow diode inside the machine next to the bios-battery is on constantly.

I have checked all the connections to the motherboard I could think of, including main power, front panel power, front panel connectors and a few others.


I could really use some help since I seem to have hit a wall and don't really know what the next troubleshooting step might be.

Thanks in advance
   Pelle

6 Replies
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Moderator
Moderator

RE: Precision t7400, No response to power button.

Hi Pelle,

Based on your post, I see that the power supply is working and I assume the motherboard is fine as well, as you state the fans, ODD and HDD turn on. I would suspect a faulty/loose memory module or the graphics card.

Firstly, confirm if the power button is functional. If yes, then try the below:

Download the service manual - http://dell.to/1AtunVj - try removing / reseating the graphics card and each memory module and check if the system powers on. Make sure to disconnect the hard drive cables before you try this step.

If the power button is not functional, then disconnect the I/O cable connecting the power button assembly to the motherboard and check if the system turns on fine.

Keep us updated.

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2 Bronze

RE: Precision t7400, No response to power button.

I have removed, cleaned and returned the RAM and Graphics card. This had no effect.

How would you recommend that test my power button assembly? A have checked the connections and they seem fine, though I am afraid to remove the I/O cable (the broad one) as it wont release with any amount of force I'm comfortable with exerting on it. I'm afraid of breaking something.

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Moderator
Moderator

RE: Precision t7400, No response to power button.

The I/O cable connects the power button assembly to the motherboard. Follow the cable from the power button assembly to the motherboard end and disconnect the cable at the motherboard end.

Let us know if this works.

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8 Xenon

RE: Precision t7400, No response to power button.

Find the green and black wires and do a paperclip test.


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2 Bronze

RE: Precision t7400, No response to power button.

Disconnecting the I/O cable from the motherboard does not allow the computer to turn on... Though I am uncertain as to how disconnecting the button will tell me anything..? I'm guessing that it won't be able to turn on with it disconnected whether the button works or not..?

I have taken the power button assembly out of an old pc for testing, but this uses a set of four 2-pin connectors instead of the gray 20-pin that's standard for this.
Any way i can still use it?

The 20-pin I/O cable is all gray so i'm not sure how to do this paper-clip test... And is it on the cable or the motherboard? How do i know whether the test is a success or a failure?

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Moderator
Moderator

RE: Precision t7400, No response to power button.

Hi uPelle,

Disconnecting the I/O cable would stop the power button from functioning. So, once the I/O cable has been disconnected, you would have to connect the power supply to the system and it will directly turn on the system - as the power button is not functional at the time.

The paper clip test is to test the functionality of the power supply unit - check this video - http://bit.ly/1dji5Dt

However, as said in your earlier post, the power is supplied to the system when you press and hold the power supply test button on the back. As stated earlier, I would still suspect one of the components, the I/O cable or the motherboard itself.