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View Full Version : Need replacement or reworked D12887 CMOS battery



TravisHuckins
June 23rd, 2017, 06:50 PM
Just when I had my DOS PC the way I wanted it and then the Dallas D12887 dies... I think it's soldered on the board without a socket... ugh. Anyone have modded D12997s with a battery socket or something?

TravisHuckins
June 23rd, 2017, 07:35 PM
How odd... it started working again. I know I should still replace it but... at least I can save BIOS now.

Chuck(G)
June 23rd, 2017, 07:39 PM
I assume you mean the DS1287 or DS12887. There are plenty of instructional sites on reworking one with a new battery. It's not difficult. Alternatively, you can purchase a DS12885 IC, a 32KHz crystal and a battery holder and roll your own.

TravisHuckins
June 24th, 2017, 11:39 AM
I ordered a new ds12887 and a socket for it. Maybe I'll try and modify the old one with a battery holder but right now I just want to get it working again. The only thing that doesn't work when the CMOS is dead is the B drive. I can still play games at least. Having the system running for about an hour restores it for a while at least.

David_M
June 24th, 2017, 12:56 PM
I got one off ebay last year for one of my pentium machines and was surprised to see it had a date code that showed it was less than a year old. Fitting it was fairly simple using my desoldering station although without one it would have been a lot more difficult than with a a 2 layer board.
My efforts turn out to be for nothing though, a couple of weeks ago I powered it up and the onboard voltage regulator fried. I think I'll just drop a 386sx board into the case rather than try to repair the board again.


I ordered a new ds12887 and a socket for it. Maybe I'll try and modify the old one with a battery holder but right now I just want to get it working again. The only thing that doesn't work when the CMOS is dead is the B drive. I can still play games at least. Having the system running for about an hour restores it for a while at least.

TravisHuckins
July 16th, 2017, 01:32 PM
Got a socket put in and put the new ds12887 and it said the memory was reduced... did I get the wrong ds12887? What amount of ram would a Gateway 2000 P5-90 need?

I just looked at the site where I bought the new one and it said it was 114 byte... do I need the 128 byte one?

TravisHuckins
July 16th, 2017, 04:26 PM
Now something must really be messed up because I can't get it to post anymore and nothing on the monitor... nothing shows up on the screen... anyone have a service manual for a P5-90 anywhere? The hard drive works in another computer... as I stuck the drive into my 32bit windowd 7 machine and a booted right into MS-DOS.

TravisHuckins
July 16th, 2017, 04:45 PM
When I was trying to get all the hardware back in the floppy drive fell and hit the heat sink for the processor... could that have broken it?

TravisHuckins
July 16th, 2017, 06:10 PM
I seriously need some help here... I have no idea what to do...

zombienerd
July 16th, 2017, 06:24 PM
Start by removing everything from the board, and reseating. It's common to knock things loose when you're digging around inside.

Just had the same thing happen 20 minutes ago on an old Dell I was installing more RAM into. It booted, then crashed, then wouldn't POST.. Reseated the RAM, and it was all good.

Be sure to use new Thermal paste on the CPU.

TravisHuckins
July 16th, 2017, 06:32 PM
I reseated the ram and the DS12887 and still no post... hard drive starts up but still nothing on screen and no beep.

Chuck(G)
July 16th, 2017, 06:34 PM
So what happens if you pull the 12887?

TravisHuckins
July 16th, 2017, 06:35 PM
Absolutely nothing... as in no change from with it in.

And if anyone has the correct DS12887 that will work in this thing let me know. As I've mentioned above the new one didn't work right.

TravisHuckins
July 16th, 2017, 06:43 PM
Though I did notice that earlier when I was trying the replacement DS12887 that some of the pins had broken off and it wouldn't post. I could somehow have messed up the old dead one that used to at least post. If I try a good DS12887 maybe it will post again.


I ordered a 128 byte DS12887 so I'll try that. Hopefully it will post again.

And if not... if there's someone that could repair my system... I would love to speak with you.

TravisHuckins
July 16th, 2017, 07:30 PM
I would kill for a service/owner's manual for this thing... it might help.

TravisHuckins
July 16th, 2017, 09:47 PM
Be sure to use new Thermal paste on the CPU.

The heat sink did not come off... I'm worried if the blow damaged the processor itself.

Chuck(G)
July 16th, 2017, 09:49 PM
Most any system will post part way with the Clock+SRAM chip removed. I suspect that you're battling something more significant. Have you tried the original chip?

TravisHuckins
July 16th, 2017, 09:53 PM
That's what I have been doing. That's why I'm afraid that I somehow broke my cpu...

If I do have to replace the cpu do you think it would be a good idea to put a bit of a faster cpu in it? Like a 120mhz Pentium 1...

Chuck(G)
July 17th, 2017, 07:16 AM
You might have also broken a support chip or even a trace on the PCB. Obviously, the latter can be repaired; the former, not as simple.