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A7N8X Motherboard Low Temperature Sensitivity, CMOS Checksum Error
Followups-To alt.comp.hardware
A7N8X Motherboard Low Temperature Sensitivity, CMOS Checksum Error SHORT VERSION: If room ambient temp drops below 25C, system is so instable it can't even complete a POST. If system is running when room temp drops, it then starts to act erratic (odd Explorer pauses and Prime95 errors), powering off then back on a dozen seconds later, fails resulting in only ""CMOS Checksum Error" and automatically booting to floppy, running awdflash. Once ambient temp rises to 32-24C, system always POSTS and runs fine. In-between these temps, failure to get beyond "CMOS Checksum Error" and errors in Windows, go up in frequency as temp drops. Multiple troubleshooting attempts have been made (Clear CMOS, BIOS flash, swap hardware, remount board in case, strip down system, etc), problem appears isolated to motherboard itself. Different BIOS, bios defaults, etc, have been tried. System is not overclocked. What are the potential cause(s) and the best methods to check these? LONG VERSION: A7N8X Deluxe Motherboard rev 2.00 Socket A, nForce2-400 Current BIOS 1008 Athlon XP2400 512MB Kingston PC3200 Fortron 400W Power Supply ATI AIW 128 Pro 1 HDD, CDROM, Floppy, (typical non-power-user PC) Approximately 1 year old, system remained unchanged for that period of time and had (guessing) about 800 hours of on-time, it was not used very much, and AFAIK, nothing demanding, it had an easy life so far. All settings were conservative, default values, no overclocking and minimal BIOS changes. Board appears to be very sensitive to temperature, but not too hot, rather too cold. If case thermometer (not motherboard integrated temp sensor but a separate digital probe) reads below approx. 27C, then powering on system from soft-off state results in system displaying the following message: "CMOS Checksum Error" Then system proceeds to do an Award BIOS recovery by booting to awdflash if appropriate floppy is already in the system. There is no option to do anything else, the BIOS setup is not accessible and the attempt to boot floppy is automatic, not a normal "boot to floppy" event as would occur with any normally-working system that has a boot floppy in it. Clearing CMOS and/or loading setup defaults does not resolve this. If the ambient temp is right at 25C or slightly higher, multiple attempts at powering off, then on, will result in system posting with setup defaults for FSB & multiplier, successfully doing so at a rate of roughly 1 in 5 tries, more often as room temp rises, less as temp falls. Even if system is manually set to same speeds or very low speed (6X multiplier for CPU and 100MHz FSB and memory), after saving these changes (or not) the system will not proceed with POST again, it takes several tries to get system to post, again displaying the "CMOS checksum Error" each time. Unplugging power supply from AC had no effect, nor did clearing CMOS. I've not pinned down the EXACT temp, since it gets progressively worse and the range is fairly tight, but it roughly corresponds to 25C-32C being fail-pass thresholds, certainly within 10C temp rise it goes from unable to POST to working fine. This has been deliberately reproduced (later) by cranking up an air conditioner, it is clearly low-temperature related, but first the steps prior to this conclusion... It does sometimes POST after saving the changes, but if then powered off it may not POST the next time... seems to still be marginal regardless of the BIOS settings, since even loading setup defaults and clearing CMOS didn't change the roughly 1-in-5 success rate. Every time it fails, the video does come up and it does attempt to boot to floppy, it never just acts dead, always has video display. Every common troubleshooting procedure I could think of was tried to no avail. Certainly more than mentioned here but due to the length of the post I'll try to list what seems most relevant. Initally suspecting BIOS corruption, I'd flashed the board with same bios version, which at the time seemed to work, but later it was discovered that the difference was instead that the ambient temperature was higher than previously, because soon enough the temp had dropped and system again failed to do anything more than "CMOS Checksum Error". The next time I had a chance I flashed the next, newest bios version, with no change. I'd been suspecting the often rumored "nvidia bios corruption" problem, which seems to occur from exiting the bios too quickly when saving settings, but this was not the case with this board. Later it was noted that doing NOTHING to system other than leaving it sit until ambient temp rose, would return system to 100% stable state. Even overclocking quite a bit it passed several different stress tests at 32C room temp, but once temp falls again, still not stable even at 6 x 100. I could understand if it these were arctic conditions but such a drastic change within a span of 10C seems quite unusual. Indeed, several other systems in same room do work fine at same temp. Also notable is that if the temp is barely high enough to get it to post and boot, running a stress test like Prime95 results in errors within a minute or so, yet with ambient temp 10C higher the system not only passes same Prime95 test for 24 hours, but can even pass it running at 50% higher FSB, Memory clock, and CPU frequency. Trying to isolate the problem I'd changed power supplies 3 times with known/proven good 400W+ units, unplugged nonessential cards, swapped video and memory, ran in minimal configuration and checked every mechanical connection as well as possible (including pulling/inspecting/reinstalling the EEPROM and jumpers), all with known good/working parts. It seems that the motherboard itself is simply intolerant of quite mild temperature drop. Normally I'd just replace it but this is quite puzzling, unique for such a small temp span, and I'd like to get to the bottom of it. There are no visable problems with the board, capacitors look fine and no visable cracking or other physical abnormalities, though I don't have the means to check this with a microscope, especially since a motherboard is a bit wider than most 'scope's reach. Since this is a very popular motherboard and I've not heard of anyone else having this problem (or perhaps they just didn't isolate the cause as low temp?) I wonder if this is an isolated flaw, but the closest examination I could make showed nothing unusual and it does work fine, never this problem (or any other that I'm aware of) once room temp rises by 5-10C. The system case is very well ventilated, ambient room temp never causes interior air temp to go up much except immediately adjacent to heatsink, as expected. I thought about the battery but voltage on it reads OK and it shouldn't explain the instability after booting and running Windows. I don't recall if I ended up putting a different battery in it or not but will do so just for the heck of it. One possibility I'm wondering about is whether one or more of the capacitors are dropping their ESR as the temp falls, if one or more are marginal and this is the cause. It might be a bit difficult to easy check this though, I'd though about possible touching a small light bulb to each in turn, individually warming them to see if that made any difference, but that could take quite a long time, especially if multiple caps are involved, since it could be necessary to wait till each cooled to try, isolate the next cap. It also seems difficult to determine their core temp without getting the outside can quite hot, as any non-destructive temp reading would be of the outer can. It seems a rather crude way of warming them too but I'm drawing a blank as to how to individually warm a capacitor without also warming the surrounding area, or at least minimizing that as much as reasonably possible. I could instead touch the leads with a solderin iron but would prefer to leave the solder alone if possible. I suppose I could take the opposite approach and warm up the board then use freeze spray on each cap, but that doesn't seem a very good approach either, since it might easily (probably would) lower the cap temp too much, introducing further failures that aren't present at 27C, not until much colder, and it again seems difficult to thoroughly chill the core of individual caps without changing surrounding area temp by this small 10C thermal margin. Another possibility I'd considered is temporarily placing a tantalum cap in parallel with (as many suspect caps as possible), since tantalums should be much more tolerant of low temp (IIRC), but this also seems to be a lengthly, tedious process that would best be avoided if anyone has a better idea? Even if I don't solve this problem I wanted to at least get this bit of info out there, that at the very least this one board is effected by a relatively small temp change, but due to the type of problem I wonder if it's more frequent, a CMOS Checksum Error is not all that uncommon and "some" of the occurrences of a Checksum Error might be misdiagnosed... and some boards not even getting far enough to post "CMOS Checksum Error" might do so if they were a little warmer. |
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