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Thread: where is the Cmos battery on an ancient motherboard?

  1. #1
    Junior Member
    Join Date
    Jan 2020

    where is the Cmos battery on an ancient motherboard?

    Since 1997 I've built 6 computers for my self and I have kept 4 of them including my current 8 core i7 9700k system. One of the computers I've have held on to is my first build
    233MHZ pentium MMX . It has a swapable drive one with win 95 the other is dual boot win 3.11 and win NT 4.0 , a Cd burner, a 3.5 and 5.25 floppy .
    So this machines spends most of it's days in the back of my closet but once in a while i break it out and fire up. so a couple of days ago I fired it up and got an error message reading
    "CMOS battery fail bios set to default"
    So the system will boot but I can't save any changes to the bios.
    Now I've changed many cmos batteries over the years but this board does not have a typical 2032 battery . I can't find the battery at all, and it's not even mentioned on the manual. I"m beginning to suspect that the battery can not be changed.
    The model is Asus P55t2P4 and it's an old style AT motherboard.
    HAs any one ever worked with old systems like this ?
    I tried keeping the computer running over night in case the Cmos battery was rechargeable but it didn't work .
    If anyone has any insight how to change the battery let me know. I would hate to see the beginning of the end for this vintage system.
    Last edited by Dannyzomb; 06-17-2020 at 02:01 PM.

  2. #2
    Administrator Steve R Jones's Avatar
    Join Date
    May 1999
    Largo, FL.
    near the upper left corner you'll see a black box on the board that has stamped on it "DALLAS, DS12B887, REALTIME, 9702A2, 088165, & pic of Alarm Clock". This is the CMOS Clock and the battery is integrated within. The entire chip must be replaced should the battery fail. Research has indicated some manufacturers has these removable/plugged into a socket.

    And this site show many pics of the show the chip with Dallas on it.
    "Vegetarians live up to nine years longer than the rest of us...Nine horrible, worthless, baconless years."

  3. #3
    Junior Member
    Join Date
    Jan 2020
    Thank you Steve , this is good information on the link. Problem is I can't figure out how to remove the DALLAS chip.

  4. #4

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