For now, I'd be tempted to just replace the RTC module, you can still buy them new with fresh batteries from places like rs-online. Maybe save the old ones and have a crack at modifying the depleted ones to use an external battery when the life of the computer isn't relying on not breaking it.

When they stop making them, then is the time to really worry about modding the old ones.

Edit: of course if you need to desolder the original from the motherboard, I'd put in a socket in before pushing in the replacement, as mentioned in the post below

I've been replacing those modules and with replacement, i have added a socket for it as well in place.

One could dremel and add other battery solution to those modules, but i haven't bothered to do that... yet...

Yes, if it isn't already socketed, the adding a socket when replacing it would be an obvious choice.

The modules are very expensive when bought new, it makes no sense for me not to add a battery to one. Cheap stuff on ebay is already past most of their life and will die sooner or later.

Tiido wrote:

The modules are very expensive when bought new, it makes no sense for me not to add a battery to one. Cheap stuff on ebay is already past most of their life and will die sooner or later.

Are you saying that the cheap ones listed as "New" on eBay are "new old stock" that may have dead batteries on arrival?
No attempt at sarcasm or anything, I genuinely would like to know.

When you look on the date codes you see they're some late 90s things or maybe early 2000s but usually at least a decade into their life. The ones you can buy from any big electronics distributor are generally only few years old.

Tiido wrote:

When you look on the date codes you see they're some late 90s things or maybe early 2000s but usually at least a decade into their life. The ones you can buy from any big electronics distributor are generally only few years old.

Right, cheers, good to know. I haven't looked that deeply into it. Only briefly searched to see if they were still for sale. My pentium board uses one, but that still seems to work. I am also considering a 386 board I've seen, and I expect it to have a dead RTC, which is why I am looking into options.

$20 AU from rs-online delivered isn't really that expensive, compared to price of the boards and processors that you are using them on.

A brand new one will probably last another 10-20 years.

I wouldn't buy one off ebay, simply because they are probably scavenged off old boards and you have no way of knowing how much charge is left in the battery.

I've got two of the cursed things, and I intend on modifying them and adding CR2032 sockets. Not looking forward to desoldering them from their motherboards, though.

Couldn’t the Dallas be replaced by some custom circuitry? Did anyone ever reverse engineer them? I mean it’s „only“ an RTC. How hard can it be. 😉

root42 wrote:

Couldn’t the Dallas be replaced by some custom circuitry? Did anyone ever reverse engineer them? I mean it’s „only“ an RTC. How hard can it be.

DS12887 drop-in replacement

Easiest/cheapest option for me was just to desolder the old one and add a DIP socket (got like 20 of them for $5 on ebay), then install a replacement Dallas chip. ($7) Plus, once you have a DIP socket installed, you could add a custom daughter board on to easily hack something together with a custom battery if needed.

Pro tip, you can get brand new manufactured DS12887A's off of Digikey for $10 if you don't like the Chinese ebay option..

Anyone know if the DS12887 is compatible with DS1287?

LunarG wrote:

Anyone know if the DS12887 is compatible with DS1287?

It is compatible.

Not looking forward to it but when my 1 and only dallas chip fails I'm doing the CR2032 hack.
With my soldering skills (or lack of) seems like the safer option and permanently solves the problem.

chinny22 wrote:

Not looking forward to it but when my 1 and only dallas chip fails I'm doing the CR2032 hack.
With my soldering skills (or lack of) seems like the safer option and permanently solves the problem.

Yes, soldering skills can be an issue. I have a 486 board that needs a new keyboard controller. I have the controller, but I need to get a better soldering iron (a soldering station actually) before I dare tackle that.
Last soldering job I did was to change the volum pot in my Akai drum machine, but I somehow think that's less fragile than a motherboard 😁

I know replacing the RTC with new replacement would look neat and tidy but in my opinion its going to go flat again in the future and that means busting out the soldering iron and replacing it again.
I did the cut and grind on my board which wasn't too hard, I don't have a dremel but I did find a small cheap grinding attachment from the hardware store that goes in any cordless drill. It was a slow process but it did the job, I was able to pull the original battery out then solder a new battery holder in place.

It worked out especially handy one time when my computer wouldn't boot/post just blank screen, in a last ditch effort to get it working again I pulled the battery out to reset the bios then put it back in and voila! the computer worked again.

Wow. This looks... interesting. Remind me never to buy a board with a Dallas RTC...

I'd take a board with Dallas RTC anyday over a motherboard using a Ni-CD battery to power the RTC circuit !