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Thread: replacing a dead TimeKeeper on a 386 mobo

  1. #1

    Default replacing a dead TimeKeeper on a 386 mobo

    Hi All,

    New member here!

    Anyways, I recently aquired a Commadore 386 PC and it has a dead ST MK48T87B-24 TimeKeeper NVRAM battery chip that is soldered to the board.
    I recently cut it out and unsoldered the remaining pins from the PCB and I was looking at a replacement chip.

    Does anyone have any experience with replacing these NVRAM chips with alternatives such as the Dallas ones or external battery versions such as the ones sold on www.exxoshost.co.uk --> https://www.exxoshost.co.uk/atari/la...w/falc_rtc.jpg

    If I understand it correctly, any of these options should work as a direct drop-in replacement ?

    Thanks.

  2. #2
    Join Date
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    .....
    Last edited by pkhoury; July 12th, 2019 at 06:53 PM.
    IBM Computers: 5150 (16-64K, 64-256K), 5160, 5161 expansion unit (several of these), 5170 (regular and Tempest) PS/2 Mods 30, 40SX, 50Z, 55SX, 60, 70, 77 (Lacuna & Bermuda), 80, 85, 90 XP.
    Vintage ThinkPads: 300, 360C/CE/CSE, 365X, 701C/CS, 720C, 730TE (tablet), 750C/P (color and tablet models), 755C/CE/CD/CDV/CX, 760ED, 770, 560/E, 600E/X.
    Vintage UNIX workstations: 2/120, 3/75, 3/60, SS 2/5/20, Ultra 2 Enterprise, HP 715/100, several RS/6000s ............And a bunch of other stuff

  3. #3
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    Did you destroy the module in the process of removing it? I've got a bunch of NVRAM/RTC repair boards that allow for the replacement of the top encapsulation with a small circuit board that contains a replacement crystal and battery in a cell holder:



    Something like that would work on the MK48T87, though the label would be wrong. I believe the 48T87 is mostly compatible with the DS12887, though in the one board I've repaired with a MK48T87, I had to use a 1287-compatible replacement as it wouldn't work with a newer 12887. I've got repair modules for those as well, and fully assembled/tested GW-12887-1 modules.

  4. #4
    Join Date
    Dec 2007
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    Texas Hill Country
    Posts
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    I've seen those before. I tried to be slick and picked up a small supply of DS12887 for some PS/2s and other systems. Semi-NOS (2013 IIRC).

    How much are your replacements, glitch?
    IBM Computers: 5150 (16-64K, 64-256K), 5160, 5161 expansion unit (several of these), 5170 (regular and Tempest) PS/2 Mods 30, 40SX, 50Z, 55SX, 60, 70, 77 (Lacuna & Bermuda), 80, 85, 90 XP.
    Vintage ThinkPads: 300, 360C/CE/CSE, 365X, 701C/CS, 720C, 730TE (tablet), 750C/P (color and tablet models), 755C/CE/CD/CDV/CX, 760ED, 770, 560/E, 600E/X.
    Vintage UNIX workstations: 2/120, 3/75, 3/60, SS 2/5/20, Ultra 2 Enterprise, HP 715/100, several RS/6000s ............And a bunch of other stuff

  5. #5

    Default

    Quote Originally Posted by glitch View Post
    Did you destroy the module in the process of removing it? I've got a bunch of NVRAM/RTC repair boards that allow for the replacement of the top encapsulation with a small circuit board that contains a replacement crystal and battery in a cell holder:



    Something like that would work on the MK48T87, though the label would be wrong. I believe the 48T87 is mostly compatible with the DS12887, though in the one board I've repaired with a MK48T87, I had to use a 1287-compatible replacement as it wouldn't work with a newer 12887. I've got repair modules for those as well, and fully assembled/tested GW-12887-1 modules.

    Yes, the old chip has been destroyed. Right now I just have the empty holes on the board.
    Im currently waiting for a new 24 pin IC socket and the NVRAM from that Exxos Atari site..

    That said, Im interested in your solution too. How much for it? and where are you located?

  6. #6
    Join Date
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    Central VA
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    I'm in the US, the repair boards are $10 (board with battery holder and 32.768 KHz crystal installed, new Renata CR2125 battery included). I typically rebuild the modules for $25 for hobbyists.

  7. #7

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    Quote Originally Posted by glitch View Post
    I'm in the US, the repair boards are $10 (board with battery holder and 32.768 KHz crystal installed, new Renata CR2125 battery included). I typically rebuild the modules for $25 for hobbyists.
    I actually got the board to work again by using that exxos solution. (next time I find a machine to fix Ill try your chip)
    20190806_220019.jpg

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