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Dell pc psu voltages


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#1 rickyict

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Posted 02 May 2009 - 10:28 PM

I have a Dell PC manufactured 03/07 that will turn on - fans runs, hard drive spins up but front light stays amber, no post, no beeps, no signal to the monitor. I figure it is either power supply or motherboard or maybe (big maybe) hard drive taken out by virus. First decided to test psu. Checked voltages at each pin (24 pin connector) and all were right on with the exception of 1. Pin #8 (gray wire on psu side of connector) which shows the status of power supply only shows +4.75 volts when charts show it should read +5. All others were correct (within +/- .03 volts). I wasn't sure if this -.25 volts was within the allowable limits for this signal. I don't have another psu with this same configuration to test. If this is acceptable, my next guess is the motherboard. But I want to rule the power supply our first.

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#2 fairjoeblue

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Posted 03 May 2009 - 12:31 AM

"Static" testing a PSU will give you an idea if the it's working but to know if it's working right it needs to be tested with a load on it.
A computer draws the most power from a PSU when it's starting.
Testing without a load only shows how much juice ot has BEFORE a draw is put on it.

The problem is Dell PSU are usually proprietary so you can't use just any to test it or the motherboard.

I suggest taking it to a shop & having it tested .
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#3 dpunisher

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Posted 03 May 2009 - 04:08 AM

Dells have been using ATX spec connectors for awhile now. I generally find it a waste of time to check each pin on the main connector. Turn the PC on and measure the 12V and 5V on a spare molex. You have to measure voltages with some load on the PSU. On old PCs that still use the 3.3v rail you might run into a problems with that diag, but usually the 5v rail will be off as well as the 5v and 3.3v share the same volt regs.

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#4 Platypus

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Posted 03 May 2009 - 06:34 AM

Pin #8 only shows +4.75 volts when charts show it should read +5. All others were correct (within +/- .03 volts). I wasn't sure if this -.25 volts was within the allowable limits for this signal.

Yes, that's not a problem for the Power Good signal.

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