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asus a7v266 bios loss of memory
once again, problems with this donor board from the friend. if you turn off all power to the p.c. through the switch on the multiplugin extention cord, on the next boot up, it goes straight to the bios and all settings are gone, well i changed out the bios battery with a brand new one, and as long as you don't turn off that switch, it keeps memory, otherwise, it goes straight to the bios. i noticed with the side of the case off, that there is a green light on the motherboard, even though the fans aren't spinning when it is "off", so i am guessing this is keeping the settings? what could cause this bad bios chip? this board is an asus a7v266 E/AA with the bios version 1011 can i purchase a new chip? i know the battery is good, would it be better to scrap this piece and go with what i have in mine, an a7v8x? thanx for any information that you can share. James Johnson -- |
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In article , "James Johnson"
wrote: once again, problems with this donor board from the friend. if you turn off all power to the p.c. through the switch on the multiplugin extention cord, on the next boot up, it goes straight to the bios and all settings are gone, well i changed out the bios battery with a brand new one, and as long as you don't turn off that switch, it keeps memory, otherwise, it goes straight to the bios. i noticed with the side of the case off, that there is a green light on the motherboard, even though the fans aren't spinning when it is "off", so i am guessing this is keeping the settings? what could cause this bad bios chip? this board is an asus a7v266 E/AA with the bios version 1011 can i purchase a new chip? i know the battery is good, would it be better to scrap this piece and go with what i have in mine, an a7v8x? thanx for any information that you can share. James Johnson Settings are stored in two places. There is a CMOS memory in the Southbridge, and it is powered by standby power sources. That is the volatile memory you are having problems with right now. The BIOS chip itself can be used to hold information, and during POST, the BIOS can actually write to portions of the BIOS chip. That probably isn't the problem, so the BIOS flash chip is not at fault. In terms of backup power sources for the CMOS memory in the Southbridge, the circuit looks like this. This is a conceptual drawing only, not a real schematic... +5VSB ---+-------------------------|---+------+-- CMOS | dual diode | | RAM glowing +---|---+ X (Southbridge) green LED | | X --CLRTC +3.0V (CR2032 ----resistor--+ | jumper battery) GND When the PSU switch is "ON", the +5VSB is running. That is one source of power for the CMOS settings. If the PSU switch is "OFF", and/or the cord is pulled from the wall, the coin cell battery takes over. The "dual diode" pulls current from whichever source has more to offer. Now, if the previous owner of the board did a "clear CMOS" operation, without unplugging the computer, the dual diode can get damaged. The path from the CMOS battery has a resistor in it, so the current level can never rise too high from that path. But the path from +5VSB is unprotected, and shorting the CLRTC jumper can draw enough current through the dual diode to burn it. Once the dual diode is damaged, sometimes it is hard to get the settings to stay there. So, there are several possibilities. The coin cell battery holder is defective, and isn't making good contact with the battery. Or, there is a partial short, and the battery is being drained within a couple of days, and then when +5VSB is turned off, the settings are lost. The third possibility is the dual diode. Judging by this description, the instructions in the manual are _wrong_. There should be _no jumper_ on CLRTC while the computer is powered or there is a battery in the battery socket. This description talks about a "glowing filament", and that could be some component, like the dual diode, burning up. http://groups.google.com/groups?hl=e...1k%404ax.co m On several Asus motherboards I've examined, the dual diode has a label on it "K45" (visible with magnifying glass, but won't be readable if burned). It is three legged and looks like a small transistor. My previous posting has some info on sources for a replacement dual diode. Another poster I helped, replaced his dual diode with a pair of 1N4148 diodes, which while having less than ideal characteristics, will work too. You will need a soldering iron, solder, solder wick (copper braid for solder removal) to do the repair - if you can buy the part, maybe a TV repair place can do the work for you. Look right around the battery socket for the three legged device. That is logically the best place for Asus to put it. http://groups.google.com/groups?selm...0192.168.1.177 HTH, Paul |
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