Question Cannot Access BIOS with new Dallas RTC installed (Socket 5 Motherboard)

Aug 5, 2021
2
0
10
0
Hi,

I have an old computer for work which broke and I am trying to get it set back up. I have replaced RAM, motherboard, and CMOS battery (old Dallas DS12887) and I finally get it to POST.

What's interesting is that when I insert the new replacement DS12887+ into the socket that I soldered onto the board, I no longer get the errors "CMOS Battery Failed", "Memory Size Decreased", "CMOS Time & Date Not Set", but I cannot hit F1 to enter the BIOS setup. If I plug in the old failed DS12887, I get the error messages that I listed above, but I am able to enter the BIOS settings.

The original problem that I ran into is that when I plug a Seagate IDE HDD into the board, the CPU doesn't POST. My thought was to try to replace the CMOS battery, configure the boot sequence in BIOS, save the configuration and this would allow me to use the HDD and boot from it on startup. Since I am using a new motherboard, it's a reasonable assumption that the BIOS may need to be configured. It appears that since the CMOS errors are gone, the Dallas RTC chip that I used to replace is fine, but I am curious as to why I can't get into the BIOS to configure the HDD.

I'm not sure whether to focus on the CMOS battery or the HDD. I'm running out of things to try. UGHHHH! Any and all questions and suggestions are welcome.

By the way, the motherboard I am using I believe is a Socket 5 Intel Premiere/PCI II (PLATO, I think). BIOS is AMIBIOS American Megatrends, Inc. Version 1.00.12.AX1.

The only reason I want to fix it is because all of the integrated boards that plug into the motherboard are ISA boards and they do various functions on a piece of equipment in our R&D lab. They are all custom boards and there's no easy replacements. I want to get this CPU up and running, while we work on delivering a suitable modern day replacement, which is both expensive and more importantly time consuming.

Thanks!
 
Last edited:
from quick google search:
Some PCs, after replacing the clock, will not properly initialize the new one. Apparently, some
BIOS versions expect the RTC to be partially initialized before it is placed on the motherboard.
Only the manufacturer of the motherboard will know how the clock needs to be initialized. PCs
with marginal power supplies, especially if they have a large number of drives, cards and/or
memory, may cause the new clock to fail. The clock can fail immediately, or within a few days or
weeks.
http://dgmag.in/N1/Online/advanced/48629.pdf

if you still have old RTC chip, you can hook up to it external battery
https://www.jelora.fr/post/2019/05/14/Reparation-puce-RTC-Dallas-DS12887-ou-equivalent.html
 
Last edited:
Yup, the Dallas RTC includes essentially some NVRAM and I suspect it has to be either preformatted the way the BIOS expects, or else has some default values stored in it from the factory. The normal way is to scrape off the top and glue a coin cell holder right on the top.

I would be very hesitant to use AAs like in Kerberos' link unless they were Energizer L91 cells, which never leak (or if they do never produce a corrosive substance)

Core 2 boards with ISA slots weren't too rare but Socket 1151 ones are https://www.tomshardware.com/news/spectras-new-lga1151-motherboard-1992-pci-slots
 
Aug 5, 2021
2
0
10
0
Gotta love that design! no wonder it is out of existence. I didn't like having to solder it off of the board to replace. I'll get out the Dremel and try to do the fix to expose the terminals and glue on a CR2032 battery holder. I'll send out an update after.
 
Actually, your 430NX Neptune chipset was the very last one to use the Dallas RTC because the very next year in 1995, Intel went to the PIIX southbridge on 430FX which integrated RTC functions including a small amount of RAM to hold the CMOS settings, driven by a coin cell battery.

The big story then of course was that Intel finally got so fed up with the data corruption bugs in the 3rd party RZ1000 and CMD640 IDE controllers that they integrated their own IDE controllers into the southbridge for the first time. To this day, drivers for those two older disk controllers disable all of their performance-enhancing features to workaround the data corruption issue, making their performance even worse (they were bad enough already as they were PIO-only, so another 30% performance drop hobbled them badly).
 

ASK THE COMMUNITY