Power supply problem?

[glatt]

My home PC is having intermittent problems. How can I tell if it's something like a power supply that I can fix?

I don't remember the model. It's a 5 or 6 year old Dell desktop that was very good in its day. Sometimes, when I go to turn it on, I push the power button, and nothing happens, except the button flashes amber. It's supposed to turn solid green. There are 4 diagnostic lights on the back, and none of them light up, which according to the diagnostic stuff on the web, means the PC isn't plugged in, or it's got some pre-BIOS error. (I think that's what it said, but it was 2 weeks ago that I looked it up.)

When I unplug the PC for 5 minutes or so, and then plug it back in, it has started up again when I push the power button. My wife just called and said that she tried that trick and it didn't work.

I'm guessing, with no knowledge and little evidence, that it's a problem with the power supply. My experience working inside computers is limited to adding RAM to this very same PC about 3 years ago. I have some confidence, but I have very little experience with electronic circuitry. I own an auto ranging digital multimeter. Is there any way I can see if it is the power supply? And if it is, are they easy to replace?

I should add that a couple weeks ago, it got infected with some virus or other malware, and I spent an evening of running scans over and over before they fixed the problem. I thought it fixed the problem, but maybe not?

[elSicomoro]

It sounds like the power supply...I have a similar problem with an old Dell Latitude laptop that I have. Does your battery recharge at all?

From looking inside mine, it seems like an easy repair, but I've never done it with a laptop before, so I might be talking out my ass.

[glatt]

No battery. It's a desktop.

I just looked up some instructions online for testing a power supply. It's fairly involved. But I can print them out and give it a shot.

[tw]

Originally Posted by glatt

I just looked up some instructions online for testing a power supply. It's fairly involved.

Procedure is simple. First, do not disconnect or remove anything. Buy or borrow a digital meter. Set to 20 VDC. Measure a purple wire from PSU where it connects to the motherboard. It should read about 5 VDC. Report that number to three digits.

Measure the green and gray wires both before and when the power switch is pressed. Report those 3 digit numbers.

And finally, set the system so that it is accessing as many peripherals as possible. For example, download from the Internet, while playing complex graphics (ie a movie) on the video controller, while powering multiple USB devices, while playing a CD, while playing sound loudly, while ...

Measure any one yellow, oranage, and red wire while all these devices are powered. Also report those three numbers. The next reply will actually report what is and is not defective without doubt.

A power supply tester is virtually useless. Cannot report many power supply failures. Do not report about other parts of the power supply system. No numbers mean a reply can only be speculation.

[glatt]

I already disconnected everything from the PSU by the time I read your post, tw. I was unable to get any readings at all from the female connectors of the PSU. I think the prongs of my multimeter are a little too fat to fit inside them. I did do the hot wiring thing from the 3rd pin to the 4th pin. That's supposed to run the fan. I plugged the PSU in, and the fan ran for about 5 seconds and then stopped. I tried unplugging and replugging several times, but the fan doesn't run.

Your idea to leave everything connected and take measurements while the system is running all the peripherals won't work here because it won't start up.

I"m going back in, and I'm going to see if I can figure out a way to get a measurement from those pins.

[elSicomoro]

Sorry...I misread your post. Thought you said it was a laptop...I'm not even drinking yet!

Changing a power supply in a desktop is pretty easy...I've done it, and I'm not the most savvy of computer people.

[BigV]

Hey glatt.

I have a power supply tester. I could loan it to you, or you could find a local shop that can test it, kind of like some auto parts stores that will test your alternator or battery for you. Replacing one is very straightforward if you decide to do that.

By the way, my tester is dead simple to use. you unplug it from the computer, plug it into the tester and read the lights.

wait.... I just went to go find it so I could take a picture for you... I can't find it. I will have to withdraw my offer to loan it to you until I can find it. I'm sorry.

[BigV]

One man's "virtually useless" is another man's "good enough".

I've had good results using the tool, since I value my time at a rate high enough to warrant replacing a powersupply as a unit compared to evaluating it component by component.

[glatt]

Turns out I either don't know how to use my auto ranging meter, or it's crap. It won't settle down on a known value even when I try it on a working battery.

So I wen old school and just bought a cheap analog meter from Radio Shack.

The green wire that runs the fan is at 4.0 volts.
The purple wire is at 4.4 volts.
The red wires are at zero volts.
The orange wire is at zero volts.
The white wire is at zero volts.
The blue wire is at zero volts.
They gray wire is at zero volts.

All measurement were on disconnected wires with no load. I think the power supply is broken.

How do I find a proper replacement? It's a Dell Dimension 8400.

[tw]

Originally Posted by glatt

Turns out I either don't know how to use my auto ranging meter, or it's crap. It won't settle down on a known value even when I try it on a working battery.

So I wen old school and just bought a cheap analog meter from Radio Shack.

An analog meter is best relocated to a bin. Meter must be digital.

Now, assuming those numbers were from a digital meter, well, a power supply is actually two supplies. One to power a system that says even when the CPU can execute. It had to measure 4.87 or higher. A number determined, in part, by how a digital meter operates.

A defective supply can still boot the computer. Also important is to confirm purple, red, orange, and yellow wire voltages on the new supply after installed. Others have seen resulting failures even months later that could have been identified long before its warranty expires.

Best would be to return the analog meter. Then buy a superior product from Wal-Mart. Or even a $5 meter from Harbor Freight. Analog meters are useless. See that number 4.87? Analog meter cannot measure to three digits.

Back to the auto ranging meter. What does it measure for a 9 volt battery? It may have been bouncing because that was your problem. A failure that might have been identified even months ago when a defective supply was still booting that computer.

Best is to confirm voltages on all six wire are now correct. Identify a failed supply months or a year before it causes computer crashes.

[glatt]

Originally Posted by tw

Back to the auto ranging meter. What does it measure for a 9 volt battery?

I was really frustrated with it, so I tested it on a 6 volt lantern battery. It was bouncing around at almost zero volts the entire time. And I think it settled down at around zero volts for that good battery. I was certain I had the dial indicator set for reading DC voltage. This same meter works fine with AC home electrical service voltage when the dial is set to the AC setting. It's made by Extech and cost me around $40 several years ago. I think I hate auto ranging meters.

When I used the old school analog meter on the 6 volt battery, it read something like 5.5 volts. And I also used the old school analog meter on the outlet, and it read around 115v.

The computer works now, and it would be a hassle to unplug the cables, pull it out from under the desk and take the measurements you are suggesting. Plus, I'd feel the need to buy a third meter, because the analog one is admittedly not so accurate. (But at least it works and is exponentially more accurate than the auto ranging one I own.)

[tw]

Originally Posted by glatt

I was really frustrated with it, so I tested it on a 6 volt lantern battery. It was bouncing around at almost zero volts the entire time.

Meter may not have been on its DC settings.

An autoranging meter will default to measuring AC voltage. A 6 volt battery measured on an AC setting would bounce about until it settled at zero volts. Something to check before binning that meter.

Analog meter may be good for harsh environments such as modifying AC house wiring. Measuring a battery for life expectancy. Or learning why/if a car battery is defective. Keeps an autoranging meter from falling into a car's radiator fan. Then you do not have to use words not found in the dictionary - such as "whoops".

[zippyt]

grab an iphone pic of the part tag ,
go to Biglots , Circut city , etc,,,
find the geek squad ( or a Neardy looking Pc dude ) ,
show him the pic
if its a 350 watt PS Snag a 450 ( More available power )
count on about $45-65 ish ( yeah I bet V or TW can find 1 cheaper )
Its Not hard changing a PS , just follow the instructions ,
get one with the Fancy blue Led in it , it looks cool in the dark

[BigV]

? replacement location pretty easy, google glatt's friend /mongo:

http://www.google.com/search?q=Dell+...a329ff265db1bb

[glatt]

yeah, yeah, yeah...

I'm really clueless about this. Clearly, if somebody has the exact original part for sale, it's gonna work, but are there other options? Can I upgrade and get a more powerful one that might even be cheaper because it's more common? Will other ones work too? Several of the ones that show up on Google (with the same exact part number) are 300 watts, while mine is 350. Will that work? Doesn't sound right to me.

I found a seller on Ebay who sells new ones, but it will take a week to get here. My wife is keen to have it fixed tonight. I think I'm just going to take the old one to Best Buy tonight and talk to someone there to see if they have something that matches. If I have the old one with me, presumable I can check to make sure the connectors and wire colors are all the same.

Just for kicks, here's the sticker on mine.