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Resolved Question

How to change the CMOS battery on an old computer?

Jun 1, 2013 7:27AM PDT

I have an old computer that I occasionally use and today I found that the CMOS battery is now dead. I opened the case and thought I'd find a small 3 volt battery that's common to so many motherboards but I didn't find that. I'm very sure that the motherboard is a Shuttle Hot 541. But when I checked the internet for info on where the battery is and how to replace it, I found nothing. Here is a photo of the board http://mail.lipsia.de/~enigma/neu/pics/mainboard_i430fx66.jpg I'd appreciate any help in changing it out. Thanks

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chafer444 has chosen the best answer to their question. View answer

Best Answer

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Thanks
Jun 1, 2013 8:21AM PDT

I actually found this page earlier this afternoon, but I wasn't sure about that post until I read the one from Bob. Putting them together helped clear it up.

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Here's a place to get a Dallas DS12887a
Jun 1, 2013 12:02PM PDT
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(NT) Thanks I'll check it out.
Jun 1, 2013 12:20PM PDT
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Answer
That's in the ds1287a chip.
Jun 1, 2013 7:44AM PDT

You can google for datasheets but the ds1287a device has a battery in it. These should be good for over 10 years.

That board looks familiar. You might see a sticker with make and model on one of the slot connectors.
Bob

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Thanks
Jun 1, 2013 8:43AM PDT

I did find the datasheet and I looked on the internet for Dallas Semiconductor. I checked their website for this product and it came up with no hits, because it looks like the ds12887a is a replacement for the ds1287a. I Googled it and got a number of hits. Since I've never bought anything like this before I'm a little unsure of where to go. One of the hits was Amazon and there were several different prices. I'll speak to a person I work with, but if you have a place that you'd recommend I'll check it out. This seemed so much easier when I thought I'd be changing a 3 volt battery.

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Sorry but it appears I need to fill in for the missing item
Jun 2, 2013 1:10AM PDT

This device was put out because there was pressure to reduce parts and costs in those models of the PC. Folk back then were getting upset about yearly battery replacements and back then some makers were using proprietary battery packs or making it non-user serviceable.

So Dallas Semiconductor saw an opening for a RTC that included it's own battery and could work without external power for over 10 years. In those models there is no battery to replace.

It's a shame the make/model and documentation on this board is not supplied as I may be able to check if there is a way to add a battery.

Are you sure this board works? It's way past it's shelf life and socket 7 boards were twitchy even back then.
Bob

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Yes the board has been working
Jun 2, 2013 5:13AM PDT

very well until yesterday when I noticed the time on the clock was wrong and then I saw that the computer no longer knew it had an A drive. I figured this was a symptom of the CMOS battery going bad. On my newer computer when the CMOS battery went bad I noticed the computer did some odd things, but they went away once the battery was changed. This old computer is 17 years old, but it doesn't get used very often which is likely why it's lasted so long. I wish I had more detailed documentation on the motherboard. I dug up the receipt that listed all the parts that went into the computer, but didn't see anything which would give more details. Although in my searching yesterday I found this diagram which appears to match my system http://stason.org/TULARC/pc/motherboards/S/SHUTTLE-COMPUTER-INTERNATIONAL-INC-Pentium-HOT-541.html#.UauUAthwe6E

I want to make sure I understand, I should be able to buy an RTC and replace it on my own and hopefully fix all of this?

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I can't answer that question.
Jun 2, 2013 5:33AM PDT

These boards have been out of production for a very long time. In fact, in a move to reduce costs that part is usually soldered in. I can't answer if you will find the part and have the tools and skills to replace it.

If there is a chance, close JP11 and then remove JP11's jumper. Maybe it will reset and work for a bit longer. I don't see the old option of another battery to stand in.
Bob

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I took another look
Jun 2, 2013 7:44AM PDT

at it and tried pulling on the RTC, it didn't seem to budge, so it probably is soldered in. As for the JP11, I thought I located it, but the item I was looking at seems to be soldered to the board too. I noticed on the board were some other things with JP's so I looked for JP11 on the board. I saw that printed next to the RTC and the BIOS chip. The item next to the print "JP11" is two pieces of metal pointing straight up. I know that's not the right technical jargon but it's the best I can do. I'm not sure what I can or can't do from this point on.

It is odd that last night when I was looking for the RTC to check on prices, I got the idea that anyone could buy one and replace it like it was RAM or something else, but I guess that's not true.

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You're a newbie
Jun 3, 2013 12:33AM PDT

I get the feeling this maybe too much for you. You can try and all that, but according to your answers it will be rather new experience. You're getting to do techie type stuff for the real fix, though it maybe simple techie fix. I mention that as anything you may try could cause further issues or problems. i will part with a possible fix, provided you can do it and if you really want that PC to work again. Understand, if there is any data on that old PC you want you can swap the HD into an adapter or ext. USB case to retrieve data. If on the other hand, that PC is specific to some task, then maybe my fix will do.

You need to be absolutely sure of the specs of that DS12887A chip. From two(2) legs that are part of it will be the +/- voltage outputs. There you solder on some small wire leads, to be +/- then attach to battery harness or cradle. You now have fresh batteries and apparatus to exchange those when dead. Otherwise, you would need a new DS12887A replacement chip for old one. Yours is probably soldered-in and thus you need to unsolder and place a IC socket in its place. Then mount new chip ordinated properly and set it up as usual. As you can see it gets complicated if your talents don't match the task. Some techs may simply solder an IC socket over the old DS12887A, making sure of no shorts and mount the new chip on top or battery setup. -OR- Looking at the spec sheet I see pin 24 is Vcc(voltage +) and pin 12 is ground(-) this is where I attach +/- wires if done that way. The battery setup is supplying ext. power directly to the chip as the old int. RTC one is weak or dead. The spec sheet Vbat reference is for the int. RTC battery.

*NOTE* anyone can correct me if i got the pins wrong here.

http://www.datasheetcatalog.org/datasheet/maxim/DS12887A.pdf
http://pdfserv.maximintegrated.com/arpdf/Packages/24pin700milmodule.pdf

http://www.mouser.com/Search/Refine.aspx?Keyword=700-DS12887A

If too much, get another newer, faster, powerful all you ever wanted mtrbd. to replace old one. Your old setup is at least 10yrs. old and not much can be had from it unless you deem otherwise.

tada -----Willy Happy

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About JP11.
Jun 3, 2013 12:39AM PDT

It's not to be removed but a jumper block placed over it, the machine powered up, then down then remove the jumper block then power up and set the CMOS settings and hope they hold.

These models were built for a purpose to avoid adding what folk were gripping about back then and had a 10 or so built in life span. As I noted, the socket was unusual to find because that's added cost so again, not much for me to add here.

Your replies tell me that you must have inherited or found this old gear. I'm sure there are socket 7 boards for sale out there. But more current machines are under 99 bucks now so it's rare to see anyone try to save such an old PC.
Bob