Battery is either practically dead, or there's a "clear CMOS" jumper on, or the motherboard expects a slightly different model of Dallas RTC - check if it has pin 21 and if so make sure the socket doesn't connect it to ground.

jmarsh wrote on 2024-06-06, 22:49:

Battery is either practically dead, or there's a "clear CMOS" jumper on, or the motherboard expects a slightly different model of Dallas RTC - check if it has pin 21 and if so make sure the socket doesn't connect it to ground.

I have had a thorough look for a clear CMOS jumper, but was unable to locate. Thanks for the pointer about it expecting a different RTC, I'll check that out. It currently has a ds12887 installed.

Sounds like a dead Dallas battery to me. I assume the date code is from the 90s or no?

Dan100 wrote on 2024-06-06, 23:14:

I have had a thorough look for a clear CMOS jumper, but was unable to locate. Thanks for the pointer about it expecting a different RTC, I'll check that out. It currently has a ds12887 installed.

If it's really a DS12887 and not a DS12887A (or another variant), it doesn't have a reset pin so the only answer is that it's flat.

jmarsh wrote on 2024-06-07, 00:15:

Dan100 wrote on 2024-06-06, 23:14:

I have had a thorough look for a clear CMOS jumper, but was unable to locate. Thanks for the pointer about it expecting a different RTC, I'll check that out. It currently has a ds12887 installed.

If it's really a DS12887 and not a DS12887A (or another variant), it doesn't have a reset pin so the only answer is that it's flat.

I'm a bit of n00b, but how do you know which Dallas RTC chip you need? I have both of the attached chips, but I don't know which pin out is correct or which one I should be using. Also, can you check the voltage across a couple of pins with a multimeter?

Dan100 wrote on 2024-06-07, 03:32:

I'm a bit of n00b, but how do you know which Dallas RTC chip you need? I have both of the attached chips, but I don't know which pin out is correct or which one I should be using. Also, can you check the voltage across a couple of pins with a multimeter? 20240607_132741.jpg

The one is from 1995 and the other is 2000. Those batteries are dead.

The "C" variant adds a century byte to the RTC.
The "A" version, as previously described, has a pin for the CMOS RESET jumper. A non-A will work on a board expecting an A, but the CMOS RESET jumper won't work. An A will work on a board expecting a non-A unless the would-be CMOS RESET pin is constantly shorted, making the Dallas chip non-functional.
The "+" variant is lead-free and is the only new version available.

Go to Digi-Key and buy one. The DS12C887A+ is the cheapest, and is what I use, although they are within a dollar of each other and cost about $13.
If you accidentally buy an A and it isn't compatible, I think you could break off the affected pin???

jakethompson1 wrote on 2024-06-08, 00:23:

The one is from 1995 and the other is 2000. Those batteries are dead. […]
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Dan100 wrote on 2024-06-07, 03:32:

I'm a bit of n00b, but how do you know which Dallas RTC chip you need? I have both of the attached chips, but I don't know which pin out is correct or which one I should be using. Also, can you check the voltage across a couple of pins with a multimeter? 20240607_132741.jpg

The one is from 1995 and the other is 2000. Those batteries are dead.

The "C" variant adds a century byte to the RTC.
The "A" version, as previously described, has a pin for the CMOS RESET jumper. A non-A will work on a board expecting an A, but the CMOS RESET jumper won't work. An A will work on a board expecting a non-A unless the would-be CMOS RESET pin is constantly shorted, making the Dallas chip non-functional.
The "+" variant is lead-free and is the only new version available.

Go to Digi-Key and buy one. The DS12C887A+ is the cheapest, and is what I use, although they are within a dollar of each other and cost about $13.
If you accidentally buy an A and it isn't compatible, I think you could break off the affected pin???

Thank you so much for taking the time to explain that to me! You're too kind.

jakethompson1 wrote on 2024-06-08, 00:23:

The "A" version, as previously described, has a pin for the CMOS RESET jumper. A non-A will work on a board expecting an A, but the CMOS RESET jumper won't work. An A will work on a board expecting a non-A unless the would-be CMOS RESET pin is constantly shorted, making the Dallas chip non-functional.

They still function, they just forget everything (except the date/time) when the power goes off. That's why it's hard to tell from a mostly-flat battery.

Still not as bad as someone swapping a Houston Tech RTC into a board not meant for one - the Houstons have no built-in crystal so if the MB doesn't have one connected to pins 2+3, the RTC doesn't tick...

jmarsh wrote on 2024-06-08, 05:24:

jakethompson1 wrote on 2024-06-08, 00:23:

The "A" version, as previously described, has a pin for the CMOS RESET jumper. A non-A will work on a board expecting an A, but the CMOS RESET jumper won't work. An A will work on a board expecting a non-A unless the would-be CMOS RESET pin is constantly shorted, making the Dallas chip non-functional.

They still function, they just forget everything (except the date/time) when the power goes off. That's why it's hard to tell from a mostly-flat battery.

Still not as bad as someone swapping a Houston Tech RTC into a board not meant for one - the Houstons have no built-in crystal so if the MB doesn't have one connected to pins 2+3, the RTC doesn't tick...

That's almost what happens to the motherboard I have. It appears to remember the date, but I'll purchase one from the site above and that will give me the answer.