Craziest thing!! The old computer that assorted spare kids use for surfing and homework has shown signs of a dead CMOS battery. The only thing is - I can't find the battery on the board -(An Asus ISA-486S) Any ideas anyone? Thanks Theo

I have looked at two diagrams of that board and cannot see any sign of a battery. There are two possibilities. Either it has a battery permanently wired into the Motherboard. Look for something like a ribbed capacitor on its side with wires at each end. There is also the possibility that the battery is a actually integrated with the BIOS chip. If that is the case and it is the battery then you are stuffed I am afraid. Couple of sites that might help. http://th99.dyndns.org/m/A-B/30319.htm http://www.cyberdelix.net/tech/isa-486s.htm Stuart

Some older models used a Dallas or similar (Houston, Odin) chip package instead - something like this often difficult to remove or replace - might see if you can connect a (so called) 'external battery' if that's the case I'm not insensitive, I just don't care.

jboy maybe very correct, according to this diagram, the clock chip at the top left looks identical to what he posted on his link, I think you may be stuffed on this one. B4 you criticize a bigger man, walk a mile in his shoes. That way, you're a mile away, and you have his shoes.

Yeah, those things can be a pain. I don't see connectors for an external battery on that schematic, but it can't hurt to look. If they exist, likely near the internal battery and marked 'Ext.Batt.', maybe a '+' for polarity. I'm not insensitive, I just don't care.

Yep, that is the DALLAS DS1287 RealTime Clock chip. It has the CMOS Clock, the CMOS data area and the battery. Life about five years. Look at the board and the DS number carefully and see which one you actually have on the system board. The real old ones used a DS1278 which you can no longer get. This was replaced by the DS12887 which you can still get. Normally a DS12887A (with its extra pin) can be used to replace it. Cost of these parts are usually around $25 to $40. But I have seen them for less. I have even seen them in Radio Shack stores that still carry computer parts. So while hard to find, its not impossible. The actual part on your board might be a Houston Tech HT12888 or HT12888A which are harder to find. Check this application note One thing to be careful about, their shelf life is the same as their life in the system. If they have been setting on the shelf for a few years, then that much of their usable life is gone. And as noted in the article, it can be a real problem getting a replacement to work right. Sometimes takes a CMOS dump and restore program to get them going correctly.

Thanks for the help. Yep, you're right guys. The offending bit is a MK48T87B-24 Timekeeper RAM and is probably not worth repairing. Thanks for your quick help. Theo