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Replace Dallas RTC battery without desoldering?

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First post, by precaud

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The answer is a qualified yes. As long as you have clear access to the side of the chip that has the terminals that need to be exposed, it is actually quite easy to do with the chip in place. You only need to be able to see what you're doing, and get the Dremel tip into the body of the chip without touching anything else. The material in these Dallas chips is quite soft, so the Dremel is easy to control..

Not having to desolder the chip turns this into an easy process. I did the DS12887 in an Intel Plato board this afternoon in a little over an hour. If it weren't for the 1/2 hour cure time needed by the epoxy, it would have taken about 40 minutes.

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  • DS12887a.jpg
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    DS12887a.jpg
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    The Pin 1 side is marked by a dot in the corner. The terminals to expose are on the other side.
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    Fair use/fair dealing exception
  • DS12887b.jpg
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    DS12887b.jpg
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    79.01 KiB
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    The green arrow shows the narrow land that needs to be cut open to disconnect the internal battery.
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    Fair use/fair dealing exception
  • DS12887c.jpg
    Filename
    DS12887c.jpg
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    101.5 KiB
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    Epoxy the CR2032 holder with the + pin touching the + terminal on the chip, as shown.
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    Fair use/fair dealing exception
  • DS12887d.jpg
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    DS12887d.jpg
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    158.8 KiB
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    Then solder it, and a wire from the - pin, to the chip terminals.
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Reply 1 of 2, by JudgeMonroe

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I’m glad this worked out for you! I just know if I tried it the Dremel would slip and tear up the board. Maybe I can mod the one I desoldered though. I have plenty of cr2032 saddles.

Reply 2 of 2, by precaud

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JudgeMonroe wrote:

I’m glad this worked out for you! I just know if I tried it the Dremel would slip and tear up the board. Maybe I can mod the one I desoldered though. I have plenty of cr2032 saddles.

Thanks. I've done lots of board-levels repairs, and this one is neither difficult nor high-risk. The mass of the board actually stabilizes the cutting. What makes Dremmeling (a new verb?) dangerous is when the workpiece is not secured, or when the material is inconsistent, and the bit grabs and gets tossed around when it encounters different densities/materials. This is like cutting through butter. I kept the rpm's very low.

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