Strange problems

I'm trying to fix my cousins' computer and it's doing things I've never seen before:

Firstly, it's a system they built a couple years ago, and it's always worked fine.

Occasionally when I boot up the computer, I get a BIOS checksum error, so I checked the battery; it's fine. I reset the bios using the jumper & it let me boot it up.

(It runs WinXP Home)

I boot it up, messed around online for a few minutes and thought it was all good -- Unfortunately after the computer sat for several minutes, these strange lines showed up on the monitor and the computer froze completely... Nothing works. I had to use the power supply switch to actually get it to shut down, as even holding the "normal" front-panel power button down for several seconds didn't shut it down.

That's not the only strange thing: If the computer is shut down properly (or via the front-panel power button), it keeps power going to the USB ports, their USB speakers, mouse and keyboard all continue with power unless I actually shut off the power supply with the PSU switch.

It's an MSI Motherboard K9N6PGM2 with on-board video and audio, 2GB RAM, an 80 GB HD.

Any ideas at all? I've been repairing computers for many years now, and have never seen anything like this -- I'm at a total loss... Any ideas at all?

-Don

 

My first visit would be to the PSU, if you do not have one you can buy relatively cheap PSU testers. They start at around $10- but will give you a fair idea if your PSU is working OK, ebay have a big selection.

 

How did you do that? You can't do it with a multimeter unless you can put the battery under a realistic load. I would replace the battery. They are inexpensive so the loss is minimal if that is not it.

That is normal!!! The ATX Form Factor standard requires +5Vsb standby voltage be applied to various points on the motherboard when the computer is powered off but the power cord is still connected. The exception is IF the PSU is equipped with an optional master power switch and it is set to off - then the standby power is removed as well.

This standby power is necessary for the front panel power switch as well the various "Wake on..." features provided. These include Wake on LAN, Wake on Modem, Wake on Keyboard and Wake on Mouse. And in order for Wake on Mouse or Keyboard to work, since most are USB these days, the USB ports must be live when in standby (powered off) mode.

So I would start with a new battery. Be sure to UNPLUG from the wall first to remove all voltages. Do not touch the new battery with your bare hands as skin oils promote corrosion and attract dust. After replacing the batter and connecting power, boot directly into the BIOS Setup menu and verify/set date and time and check that all drives are properly identified. If fine, Save and Exit to boot normally. If still having problems, then it looks like the PSU to me. In any case, ensuring good power is the next place to look.

Here's my canned text on testing PSUs.

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range ". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed ". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Swapping in a known good supply is a tried and trued method of troubleshooting, used for years even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with a known good one and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the required voltage tolerance ranges:

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And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user serviceable parts inside a power supply.
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I also have a similar PSU tester with LCD readout and indeed one of the 12v rails is bad, so I shall replace the PSU when able.

I know that there are various points on the mobo that require power for the front panel, but I have never seen a motherboard supply power to anything hooked into USB while the power is off like this one is. Standby power doesn't normally supply power to the USB ports. (Like in this case the keyboard and usb speakers).

Nevertheless I thank you all for your replies - Hopefully I'll be able to replace the PSU soon; but as it's my cousins' computer, I must wait for them to get one..

 

That is absolutely wrong! That is the whole point of standby power! I explained it above. This voltage IS present on several points, INCLUDING the motherboard's standard USB ports whenever the computer is shut down, but still plugged in, and if equipped, the master switch is set to on. This is required by the ATX Form Factor standard, which I posted a link to, so if the BIOS is so configured, you can power up the computer simply by pressing a key on your USB motherboard or wiggling your USB mouse! And this standby voltage has been a requirement ever since the AT Form Factor standard was replaced by the ATX Form Factor standard in 1995!

Just because you have not seen it, that does not mean it is not there. You can't see voltage by looking at the plug!

Go get yourself a corded USB laser mouse. Many have a LED that remains lit at all times when plugged in to show the computer is in standby. Your speakers have nothing to do with it. Power to the port does not mean audio is present all the time. But for the record, I have a set of JBL speakers that have lit LEDs when the computer is in standby mode.

And your computer does not have a designated USB port just for speakers - that would hardly be "universal ", would it? So I say again,

If there is no power to the USB ports when in standby mode, it is because someone turned it off! And that is rarely done, except for notebooks that do so to conserve battery power. And note as I said above, in order for Wake on Mouse or Wake on Keyboard, those options must be enabled in the BIOS. That does not turn on or turn off power, it only turns on the Wake option - the power is still there.

For future reference I would suggest before you make contradictory statements, you do some research. A simple Google search might keep your foot out of your mouth. And if you confirm your belief, post a link to substantiate it. With no effort, I found this August 2004 Microsoft Knowledge Base article, MSKB 878467 - Your Windows XP-based computer does not resume from standby when you move your USB mouse or press a key on your USB keyboard. With a little more effort, I am sure I could have found earlier proof.

 

Good luck with replacing the PSU, and don't skimp on it, not in regards to watts but on terms of quality.
hawk22