Dallas battery replacement ?

Discussion about old PC hardware.

Dallas battery replacement ?

Postby Intel486dx33 » 2019-1-30 @ 06:12

Should I use an external battery or replace the Dallas battery ?
If so, What Dallas battery model do I need ?
The Socket has 24-holes for 24-leg Dallas battery.
12-legs on each side.
Which side is "+" and which side is "-"
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Re: Dallas battery replacement ?

Postby dkarguth » 2019-1-30 @ 06:42

Most of these computers use either the discontinued Dallas DS1287, or the newer Dallas DS12887/DS12887a. They are listed as "interchangeable" by the manufacturer, but they sometimes don't work correctly on some motherboards. On the socket, there is a notch out of one side that corresponds to the correct orientation of the chip. You will notice this is universal for all DIP sockets, there is a notch out of the chip that matches up with the socket. Also, that Dallas chip is not just a battery, it also has your Real Time Clock chip and some memory for storing BIOS settings.

You have several options with replacement. You can go on ebay and buy a DS12887 for around 5-10 dollars on average, and it might work. I say "might", because if it is an old chip, the battery might already be flat. Another option is to check out this link:
https://www.ebay.com/itm/GW-12887-1-DS1 ... :rk:2:pf:0
It's a replacement for the DS12887 that rather than using an internal battery, it uses a button cell on top of the chip to power it.

I'm not sure what is going on as far as the external battery option. My best guess is that you might be able to install a dallas ds12885 with an external battery? the ds12885 is identical to the ds12887 except for the internal battery. In fact, the DS12887 actually contains a full DS12885 with some of the pins bent up!
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Re: Dallas battery replacement ?

Postby keenmaster486 » 2019-1-30 @ 06:53

Ugh, once upon a time I used a Dremel tool to cut into an old Dallas RTC chip in just the right manner such that the battery terminals became exposed. I then soldered wires to them and connected them to a two AA battery pack for 3 volts. I also had to use the Dremel to sever the connection to the existing battery.

Don’t ask me how I did it or even how I knew how to do it at the time... I was crazy to even attempt it but it worked! That same PC is still working today and retains its CMOS settings.
I flermmed the plootash just like you asked.
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Re: Dallas battery replacement ?

Postby Murugan » 2019-1-30 @ 06:55

TBH I would go for the external battery. Have 3 pc's like this now and it works like a charm.

OR

https://www.classic-computers.org.nz/bl ... y-chip.htm
My retro collection: too much...
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Re: Dallas battery replacement ?

Postby dkarguth » 2019-1-30 @ 09:52

The only problem is that the dallas chip contains the actual RTC and the SRAM that stores the BIOS settings. If he doesn't install a dallas chip and installs a battery instead, it has the battery but is still missing the RTC and CMOS chip. Or am I missing something here?
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Re: Dallas battery replacement ?

Postby tayyare » 2019-1-30 @ 10:31

I bought this just a few months ago (in August) for a 486:

https://www.aliexpress.com/item/Free-Shipping-1PCS-DS1287-1187-DS1287-DIP18/32620558261.html?spm=a2g10.10010108.1000001.7.5047185fGqxp3N

It worked out of teh box and still works.
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Re: Dallas battery replacement ?

Postby dionb » 2019-1-30 @ 10:33

dkarguth wrote:The only problem is that the dallas chip contains the actual RTC and the SRAM that stores the BIOS settings. If he doesn't install a dallas chip and installs a battery instead, it has the battery but is still missing the RTC and CMOS chip. Or am I missing something here?

That depends on the type of Dallas chip.

The DS1287/12887 Realtime are just RTC and battery, the DS1387 Realtime RAMified is RTC, battery and 4k SRAM. The two are not interchangeable -if you put a DS128(8)7 onto a board expecting a DS1387 it won't boot. That's relevant, as there are drop-in replacements available for the DS128(8)7, either newly produced RTC modules by Maxim, or homebrew combinations of a simple RTC with a coin-cell battery holder. I'm not aware of any such replacements for the DS1387, there you have one option only: grab that dremel and mod the existing module to take a new battery. Which is what I'm going to do this evening ;)

TS, if you don't have the RTC that was on the board, you need to find out which was on it originally.
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Re: Dallas battery replacement ?

Postby dkarguth » 2019-1-30 @ 18:07

Ah, I understand now. Thanks for correcting me on that before I spread more bogus information! By the way, the Dallas DS1387 is simply a DS1385 with an internal battery. They literally just bent some pins up on the DS1385, plonked a battery on there, and then encaptulated it in expoxy. If you can find a DS1385, you can essentially make your own maintainable DS1387.

I looked up the motherboard, and the original diagram shows a symphony SL1287 in that socket, which is essentially a rebranded Dallas DS1287.

You seem to have the same motherboard being discussed in this thread: viewtopic.php?f=46&t=36523
The motherboard info page is this one: https://stason.org/TULARC/pc/motherboar ... F-3VL.html

Unfourtunately, I could not find the original user manual, so it was most likely one of thousands of generic motherboards produced over the years. I would start with trying a Dallas DS12887 to see if it works, most of the time it's a drop in replacement for the DS12887. There are some occurrences where it does not work, however, so your best option might be to go the 1287 + dremel route.

If you wish to find a replacement 1287 to hack on with a dremel, ebay is your friend. Same with the 12887, that's where I got mine.

Keeping track of all those model numbers is a pain, lol.
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Re: Dallas battery replacement ?

Postby Intel486dx33 » 2019-1-30 @ 19:02

Thanks for the reply's people. So I have a few options.
I have some questions:

1) Which way does the Dallas battery fit into the socket ? ( Which side is Positive on the socket ).
2) What type of coin battery can I use with the Dallas battery MOD ?
3) Some of these Dallas battery replacements have 14-legs on each side 24-legs total, as opposed to the socket on my motherboard which only has 12-legs holes on each side.
Will the Dallas battery with 24-legs it fit an work in my motherboard ?

Those 3D printed coin battery MOD's are really nice but expensive.
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Re: Dallas battery replacement ?

Postby dkarguth » 2019-1-30 @ 19:15

The battery in the Dallas chip is a 3v button cell. A CR2032 should do just fine. As for the orientation, normally you can tell 1 of 2 ways which way the chip is supposed to go. The one I have has a little semicircle shaped notch about 1/16 of an inch wide on the bottom of the chip near one of the ends. Other chips have a dot in one of the corners on the top of the chip. That dot/notch goes on the same side as the notch in the IC socket. You can see that notch in the picture you posted of the socket, it is the opposite side from the RAM slots.
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Re: Dallas battery replacement ?

Postby Intel486dx33 » 2019-1-30 @ 19:18

Okay, I got it.
Thanks everyone.
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Re: Dallas battery replacement ?

Postby dkarguth » 2019-1-30 @ 20:12

Np, always happy to help!
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Re: Dallas battery replacement ?

Postby GigAHerZ » 2019-2-26 @ 08:54

Quick tip: You can replace 12887 with 12885, which doesn't have a crystal nor battery. (Just a chip)

If motherboard supports (i'm in the middle of converting Acorp 5vx32), you can just replace it and motherboard will provide power and crystal clock. If you want, you can add the crystal and battery holder on top of 12885, therefore not needing to somehow prey the casing open or anything like that. ;)
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Re: Dallas battery replacement ?

Postby canthearu » 2019-2-26 @ 10:07

On an old PC CHIPS motherboard, I just modded the devices old 1287 chip with an external battery.

You will need a dremel, a soldering iron and a multi-meter (to check you have severed the internal battery properly).
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Re: Dallas battery replacement ?

Postby GigAHerZ » 2019-2-26 @ 10:43

canthearu, yes, i've done that as well.

Yet, with 12885 (which should be direct replacement to 12887 except battery and crystal, which itself should be direct replacement to 1287) you don't need to do anything except 4 pin soldering. It's just a classic PDIP28
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Re: Dallas battery replacement ?

Postby SirNickity » 2019-2-26 @ 21:28

As soon as I verify this fits, I'm sending it off to OSH Park. If it works, I'll publish the project and post the BOM, and you guys are welcome to make your own.

rtc.png
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Re: Dallas battery replacement ?

Postby Miphee » 2019-11-22 @ 21:18

Is the Dallas chip socketed on the IBM PS/2 55SX mainboard (57F1536)? I can't really tell and I don't have the machine yet. It looks socketed but I need confirmation, one even has a cable tie.
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Re: Dallas battery replacement ?

Postby blurks » 2019-11-22 @ 21:29

I had a 55SX. Can confirm it is socketed.
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Re: Dallas battery replacement ?

Postby Miphee » 2019-11-22 @ 21:32

Thank you!
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