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Replacing the Dallas real time clock on a 486 mobo

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First post, by retro games 100

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Mobo: UM8810PIAO, PCB revision 2.1, UMC chipset. It uses a Dallas real time chip, and its markings are:

DS12887A
9515A2 059577

I bought one of these on ebay:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewIt … em=250523279682 (Quantity remaining: over 100)

You get 2 chips, cheap as chips. And they work! I pulled the existing socketed chip off the board using a pair of pliers. I pushed the replacement(s) down using my fingers. The CMOS settings save OK. I pulled the mains plug out of the wall, waited 5 minutes, then retested the mobo. No problems. The replacement chips are marked with:

DS12887A
0419B1 340859

DS12887A
0432B1 342629

Now that this simple operation has worked, the real task is to break open the replacement chips, and replace the internal battery. But at least I can operate on them, knowing that I'm hacking in to spare chips, and not the original one.

Reply 1 of 1, by retro games 100

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I did another test, this time using a slightly different 486 mobo, a UM8810PAIO, revision 2.0. This mobo also has a Dallas real time clock, but it's labelled DS12887. (The first Dallas chip from the O.P. was labelled DS12887A.) I tried a "new" DS12887 dallas chip in it, but it failed to work. (I think this "new" Dallas chip bought from ebay is faulty - the BIOS POST message complained about the battery being dead.) I then tried an old DS12887A dallas chip. That worked! So, it appears that you can replace a DS12887 chip with a DS12887A chip.

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