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Unable to power on Dell Dimension 4550

This is a discussion on Unable to power on Dell Dimension 4550 within the Other Hardware Support forums, part of the Tech Support Forum category. I'm working on a Dell Dimension 4550 for a client. The system will not turn on. With the power cable


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Old 03-15-2010, 05:35 PM   #1
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I'm working on a Dell Dimension 4550 for a client. The system will not turn on. With the power cable attached, there is a green light on the motherboard. The power supply tested okay. I also pulled the memory.

I removed the switch and replaced it with another used one (seller claims it tested fine). However, this made no difference. Can I use a jumper to test the switch? Which pins do I need to contact.

Any other thoughts on what might be causing this problem?

Thanks!

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Old 03-15-2010, 05:54 PM   #2
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The Mobo light being on doesn't mean the PSU is good. How did you test the PSU to assure that is is not defective?
Your problems relates to a failing/failed PSU. Do you have another PSU to try?

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Old 03-15-2010, 07:08 PM   #3
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I used a PSU tester but it's very basic (plug it in, flip a switch, and an LED glows), so I don't know that it's accurate in the case of a failing, but not fully failed, power supply.
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Old 03-17-2010, 03:03 PM   #4
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I have a more thorough PSU tester on order. When it arrives, I'll post the results.
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Old 03-19-2010, 10:05 PM   #5
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Tested the PSU again with the new tester. All of the lights lit except the one for -5V.

I've read that newer 24-pin PSUs often do not supply the -5V line. However, the PSU I'm testing is only 20-pin. So, is it likely that the non-functioning -5V is the problem?
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Old 03-20-2010, 08:05 AM   #6
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Tyree ask if you had another PSU to try. I still use a digital voltmeter, even so I still double check with a known workiing PSU. As you know, the Dell PSU is not your standard PSU unit. I use a standard 20+4 pin PSU that does not have the white -5v wire. I have got a later Dell to post and load the OS with this. If it does not post, I check the motherboard diagnostic lights and see if the motherboard light is amber and if the power switch light is amber, that leads to a bad motherboard.
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Old 03-20-2010, 08:15 AM   #7
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The best test for a PSU is a substitute.
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Old 03-20-2010, 09:48 AM   #8
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Thanks for the feedback. The motherboard has a single light, which is green. The unit won't POST, and I get nothing on the power switch light.

I'll see what I can come up with in the way of another compatible PSU and let y'all know what happens.
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Old 03-20-2010, 12:53 PM   #9
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These are the diagnostic codes for the led lights on the motherboard on the back of the PC.
http://support.dell.com/support/edocs/systems/dim4550/advanced.htm#1118998
I have seen the small flat ribbon with a black end coming from the power switch that plugs in towards the front of the motherboard come loose from someone else working on it.
Good Luck

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