Asus A7V600 boots to bios password-intermittent

Hello all, I built this unit for a friend about two years ago. Three times in 2009 this machine booted up to the bios screen asking for a password-we had never used one in the bios. The date did not change but the CPU was running at its slowest speed setting (1100Mhz). The mobo is version 1.0. It has 1.5GB (3X512) PC 2700 memory. We are running an Athlon Barton 2500+ with a Seagate 320Gb SATA HDD running XP Home with all the updates.
The first time this happened I updated the BIOS with the latest available from the Asus site and replaced the battery. The second time (3 months later), I reflashed the BIOS with the latest files again and reset/reseated everything. The last time (2 months ago) I reflashed the BIOS using version 1008 (9-02-04). The customer says that in between events the machine runs great. There are no other symptoms or problems.

If anyone has run across this or has any suggestions I would appreciate the input. Thanks for your time, VC.

 

You say 2 years ago but that's an old CPU. And the fact there is a BIOS from 2004 would seem to suggest the motherboard is a bit older than 2 years too. Were these "new" when you assembled them?

I think I would replace the battery again. Even though the date and time are holding, something is changing and replacing the battery does the least damage to the wallet. I have seen new batteries fail prematurely.

My worry is the something is wrong with the CMOS. The CMOS is a special semi-conductor memory device that, by design, remembers its data only when there is a specified "holding voltage" on a designated pin. Once the voltage is removed from the circuit, as soon as the voltage "decays" past some threshold, the data is lost. The voltage can be removed by pulling the battery, or by momentarily shorting the pin (and holding voltage) to system ground (typically by the using the "Clear CMOS" jumper). The problem is, the CMOS device is not user replaceable - that would be new motherboard time.

How is he turning off the computer for the night? Is the computer left plugged in to a "live" power source? Or does he pull the plug, or power off everything with a master power switch (perhaps on a surge and spike protector or power strip)? By leaving the PSU plugged into a live power source, the ATX Form Factor required +5Vsb standby remains present across many points of the motherboard, including the CMOS, so there would be no drain on the battery. For this reason, I recommend leaving the PSU plugged into a live power source (preferably an UPS) when the computer is not in use. Only remove power completely when doing maintenance inside the computer, or if going away on an extended trip/vacation.

I would also want to ensure the PSU is good. Here's my canned text on that:

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.

As mentioned, swapping in a known good supply is a tried and trued method of troubleshooting used for years, even by pros. Remove the "suspect" part and replace with a "known good" part 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:

http://i195.photobucket.com/albums/z181/Digerati_Bill/One-Time%20Upload/PSUTolerances.jpg​

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 agree with Digerati's excellent post,there's something wrong with the cmos flash memory or the battery connection.

 

Hello folks and thank you for your responses. I believe Digerati is correct. This unit was a budget build with known good used parts. After discussing the matter we are going to replace this mobo with a new quad core set up. Thanks again for your responses, VC.