Image Map Image Map
Page 1 of 3 123 LastLast
Results 1 to 10 of 21

Thread: New way to replace ailing Dallas RTC chips?

  1. #1
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    266

    Default New way to replace ailing Dallas RTC chips?

    I stumbled on this while taking a look around eBay:

    https://www.ebay.com/itm/GW-12887-1-...4AAOSwFLBab95j

    It seems like a few easy-to-get RTC chips have been modified and able to be powered with a coin battery.

    It seems nice, but I'm slightly skeptical if it would work in-situ.

  2. #2
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    33,666
    Blog Entries
    18

    Default

    Take a look on this forum--they're the product of our very own Glitch.

  3. #3
    Join Date
    Jan 2010
    Location
    Central VA
    Posts
    4,796

    Default

    Hi there! If you wait for the Tindie listings to be approved, they're $20 instead of $25

    The module is made from a real DS12885+ purchased brand new from a major components supplier. The little PC board is my own design, it carries the 32.768 KHz crystal and 3V lithium cell that's normally buried in epoxy on the DS12887. So, in that sense, it's 100% functionally the same as a new DS12887, except you don't have to throw it out in 10 years.

    As to "if it would work in-situ," it depends on if the circuit you're plugging it in to will work with the DS12885. For everything that originally had a DS12887 installed, the answer should be, "definitely yes." For systems that use a DS1287, the answer is, "maybe." I've personally tested them in about a dozen different systems, and so far I think two haven't liked the DS1287 -> 12887 upgrade. I do have a very few GW-1287-1 modules that use NOS D1285 (the IC inside a real Dallas DS1287), but the DS1285s are harder to find in DIP packages. You can rework an old DS1287 with one of the bare repair boards -- I haven't done a writeup on this yet, but it's not too difficult.

  4. #4

    Default

    While we're on the subject, will a DS1287 work as a replacement for a DS12887? What's different between the two?

  5. #5
    Join Date
    Jan 2010
    Location
    Central VA
    Posts
    4,796

    Default

    Quote Originally Posted by Plasma View Post
    While we're on the subject, will a DS1287 work as a replacement for a DS12887? What's different between the two?
    "Sometimes." The DS12887 has differences, I don't recall them off the top of my head. The Dallas/Maxim datasheet says the 12887 is a "direct replacement" for the 1287, but experience shows that it's not a 100% solution. I haven't looked deeply enough into the problem systems to state whether it's an electrical timing issue or a software issue or what. I do know on the one PC motherboard that wouldn't take a GW-12887-1 in place of a DS1287, the POST debug card showed a failure in initializing the CMOS registers.

  6. #6
    Join Date
    May 2006
    Location
    Melbourne, Australia
    Posts
    6,535

    Default

    Quote Originally Posted by glitch View Post
    The Dallas/Maxim datasheet says the 12887 is a "direct replacement" for the 1287, but experience shows that it's not a 100% solution. I haven't looked deeply enough into the problem systems to state whether it's an electrical timing issue or a software issue or what.
    There is a 'RTC Module (Dallas Semiconductor, et al) FAQ' document floating about, and that includes:


  7. #7

    Default

    @glitch

    Kudos for your very fine work.

  8. #8
    Join Date
    Jan 2010
    Location
    Central VA
    Posts
    4,796

    Default

    Quote Originally Posted by modem7 View Post
    There is a 'RTC Module (Dallas Semiconductor, et al) FAQ' document floating about, and that includes:
    Heh, modem7 to the rescue, as usual So it sounds like it's purely a software issue. In any case, I've been saving the dead DS1287s I've replaced and will eventually rework those with GW-1287-1 repair boards, so there will be *some* stock of ready-to-go DS1287 replacements.

    I will be writing a submit-your-results compatibility matrix for the GW-12887-1 in line with the new TestFDC Registry. Not that we can test every single system in existence!

    Quote Originally Posted by lyonadmiral View Post
    Kudos for your very fine work.
    Thanks! Hopefully it makes others' vintage computer repairs easier

  9. #9
    Join Date
    Oct 2014
    Location
    near frankfurt/m, germany
    Posts
    1,012

    Default

    Same idea as here: https://www.exxoshost.co.uk/forum/vi...hp?f=20&t=9344

    It was done for ATARI Falcon 030, but as it is also just using the DS12887...

    Until now some Falcon users only drill the existing chip open until the battery contact plus pole is reached and solder a CR2032 battery holder plus to it, and holder's ground to mainboard ground.

  10. #10
    Join Date
    Jan 2010
    Location
    Central VA
    Posts
    4,796

    Default

    Yeah, you can totally just glue an external holder on, I did that in the past with a DS1387:

    http://www.glitchwrks.com/2017/07/27/ds1387-rebuild

    I think the repair board makes for a neater repair.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •