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GA-486MA/S motherboard CMOS battery replacement

W

Wayne G

New Member
Joined
Jul 24, 2021
Messages
6
Location
Melbourne, Australia
Can someone help with the location/type of battery for this old board? I've read the manual and cant find where/what type of CMOS backup this board has.
I've removed the board from the tower and can't see anything that looks like one.
I'm running an old Intel 486 DX4 100 Overdrive CPU which starts ok but the BIOS memory doesn't save on exit and hard drive settings are lost.
Cheers Wayne
 
On your motherboard, do you see the BIOS chip (271024)? Right next to it is another block-ish chip (24 pin) DS12887, which is your RTC and battery all rolled up into one (datasheet here). Although there are some hacks that involve carving into the resin potting compound, the straightforward approach is to replace the chip itself (and add a socket for it for the next time). The DS12887 is in current production; buy a fresh one, not one from eBay, unless they can guarantee the manufacture date. Glitch (on this forum) also makes kits with replaceable coin cells.
 
Thx Chuck, cant see those numbers on the chips. I made a typo on the board and couldn't edit it. It is actually GA-486AM/S VER 2.1A. It has an Award software chip L4779500 & a blockish chip labelled BENCHMARQ bq3287MT.
 
I think you've pointed me in the right direction Chuck, thanks heaps. (Would have helped if I had of given you the correct M/B part number in the first place!) I searched the BENCHMARQ and it's an RTC with battery inbuilt. Fortunately it's on a socket. I'll order a replacement and hopefully the hard drive settings will save then. Cheers Wayne
 
The bq3287MT was (no longer made) TI's DS1287 clone. So a DS12887 should still be fine. Since the TI chip has long been EOL, finding a good one of those where the battery isn't depleted may be a little daunting. A fresh new DS12887 or Glitch's little PCB with coin cell would be the preferred route.
 
Thanks Chuck, I found a couple of 'new' BQ3287's yesterday and ordered them. Hopefully batteries aren't shot. It will take about 3 weeks to get way down under from the US to me.
I'll let you know how I go. If no good I'll go down the other path.
 
So they're probably compatible? I haven't tried to use one yet, but heard from at least one person that they'll work.
 
That’s interesting on the datasheet where it shows drop in replacement for IBM 5170. Has anyone attempted that? Would that be a good solution for the hard to find batteries? I’d think that would be safer too, less risk of leaks from some triple A or even the stock style battery.
 
Thanks for the help everyone. I found a couple of 'new' 3287's online and thought I'd try them first. Same issue, hard drive info not saved when I exit BIOS. As Chuck said, batteries probably shot by now too. Another member messaged to say he does modified chips with external battery so I'm waiting for a price for one of them.
 
Thanks everyone for your input. I decided to take to the chip with the Dremel. Succeeded in exposing the old battery and connected an external one across pins 16(-) & 20(+). All started working for awhile. I then shutdown and tried to restart. CMOS is now happy and data is retained but the C drive started clunking & clattering and fails. Anyone know a common cause and if the old hard drives can be repaired?
It's a Maxtor 7420AV.
 
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