Many other computers from the 90s used them as well. Throughout their lifetime, they do keep good time. Their lifetime is also quite long. Modules that are well over the stated lifetime of ten years may continue to keep time for another five years or so. The only serious drawback is the battery inside the module does eventually fail. When it runs down, you are left with the task of finding a new module and then justifying the purchase price against the actual value of the computer itself.

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The usual reason for these errors is a flat CMOS battery. In most machines this problem is easily rectified, simply requiring an over-the-counter 3 to 6v battery replacement on the motherboard. However the process is not always quite so hassle-free.

Along with the real time clock this chip also holds the CMOS battery, all entombed together in a compact plugin unit. Rather neat perhaps, until the battery goes flat in which case the whole chip needs to be replaced! That is assuming you can get the part in the first place.

Not easy when dealing with a computer over 20 years old. Every time I booted up the machine, I was greeted with the errors above. I needed to do something about it! Almost immediately I found an article written by someone who had the same issue and had published a solution. It involved hacking away parts of the chip, then rewiring an external battery onto it. Following the web article I hacked away the chip material with a small serrated knife. I found the substrate quite soft and easy to cut into.

Photo 2. Exposing the contacts inside the DS chip After these pins were exposed, breaking the connection to the internal battery was easy. All that remained then was to simply wire up a button battery holder to the exposed metal.

My hack job can be seen below. Photo 3. Dallas chip with new external battery After making sure the solder was firmly connected it was a matter of inserting a 3v lithium button battery into the holder photo 3 , replacing the chip on the board and screwing the PC cover back on.

Photo 4. No errors, just a straight boot-through as it should be. All in all, the repair took about a hour and was pretty straightforward. All power to the Internet and particular thanks to Peter. Wendt who wrote up the procedure.


DS12887 - DS12887 Real Time Clock Datasheet

Now the battery is dead, configuration is lost after relatively short time again and you get error-codes constantly. A really new, fresh and unused chip is hard to get. Even its successor DS is pretty hard to get and darn expensive. At that point you wish you could add an external battery. There are no provisions for one. Not yet. The Action: Have a look at the graphics below..



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