Here is a picture of the motherboard. It looks quite fancy to me. It must have been an expensive motherboard back in the day, but sometimes solving problems isn't the easiest thing to do.

I was most suspicious of that coin battery previous owner has soldered to one of the dallas chips and that is why I considered getting new dallas chip if ones exist that still hold charge.

I says it is non volatile RAM, which means it should store data when the system is off. As such, I would say it has a battery in it. I would change it just as a precaution.

For the DS1287, I would buy a more modern DS12887+ (not a DS12887A, as I don't think they are compatible).

I like that it has a Weitek socket as well. Weitek 4167 are not cheap, but I would love to do some testing with one some day 😀

Baoran wrote on 2020-10-13, 18:01:

Is there a battery inside dallas DS1225Y or is it just a ram chip?
I have an early 486 full size AT motherboard that has 2 dallas chips DS1287 and DS1225Y, so I am wondering if I need to change both of them or is just changing DS1287 enough. I have had the motherboard for over 2 years now and I am torn between trying again to make it work or throwing it away.

Also are DS1287 still being made? I see them being sold on ebay as "new", but I don't know what the chances are of them still having working battery inside if I bought one.

Yes there is a battery inside DS1225Y but they are no longer made according to Maxim (who bought Dallas), the DS1287 has been replaced with the DS12887. If you buy one get a DS12887 not a DS12C887.
The C mid part number denotes 113 bytes SRAM where the non-C is 114bytes. The A suffix denotes a Clear CMOS function.
Many of us have frankensteined a Dallas by adding an external battery, is quite common.
I suggest Digikey to get your Dallas chips, have bought many from them and never got one with a dead battery or some chinese remarked date coded one.....

Horun wrote on 2020-10-13, 22:23:

Yes there is a battery inside DS1225Y but they are no longer made according to Maxim (who bought Dallas), the DS1287 has been re […]
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Baoran wrote on 2020-10-13, 18:01:

Is there a battery inside dallas DS1225Y or is it just a ram chip?
I have an early 486 full size AT motherboard that has 2 dallas chips DS1287 and DS1225Y, so I am wondering if I need to change both of them or is just changing DS1287 enough. I have had the motherboard for over 2 years now and I am torn between trying again to make it work or throwing it away.

Also are DS1287 still being made? I see them being sold on ebay as "new", but I don't know what the chances are of them still having working battery inside if I bought one.

Yes there is a battery inside DS1225Y but they are no longer made according to Maxim (who bought Dallas), the DS1287 has been replaced with the DS12887. If you buy one get a DS12887 not a DS12C887.
The C mid part number denotes 113 bytes SRAM where the non-C is 114bytes. The A suffix denotes a Clear CMOS function.
Many of us have frankensteined a Dallas by adding an external battery, is quite common.
I suggest Digikey to get your Dallas chips, have bought many from them and never got one with a dead battery or some chinese remarked date coded one.....

Do you think it might be that I have problems with the motherboard because DS1287 has that battery holder connected but DS1225Y doesn't have one?

Yes that could be an issue ! The DS1225Y does store data (some 64k worth) so if battery in it is dead it will not save that data if computer is turned off. What that Dallas chip stores is unknown but must be important or they would NOT have included it in the board design. Makes me think about a old board that used a floppy configuration utility that stored data in a separate cmos like the DS1225Y and not the main BIOS CMOS. Not sure if that helps but am guessing you could fix it like the DS1287 with and external battery.

Passive cache, a modified AT in excessive use of PAL and GAL, TTL chips, motherboard to work with 486 in 16 and 32 bits mode, and pair of intel chipsets to hook into to create ISA and EISA bus and to add to the insult, 8x 30 pin SIMMs, only 2 banks, basically cheap.

A good board should have chipsets and a nice cache controller included tend to work well and quicker, more compatible, 4 slots of 72pin SIMMs.

I tend to find these a problem with some boards like this unless they were designed properly.

Cheers,

Horun wrote on 2020-10-13, 23:36:

Yes that could be an issue ! The DS1225Y does store data (some 64k worth) so if battery in it is dead it will not save that data if computer is turned off. What that Dallas chip stores is unknown but must be important or they would NOT have included it in the board design. Makes me think about a old board that used a floppy configuration utility that stored data in a separate cmos like the DS1225Y and not the main BIOS CMOS. Not sure if that helps but am guessing you could fix it like the DS1287 with and external battery.

I haven't seen any floppy configuration utility, but my main problem with the motherboard is that the floppy drives don't work properly no matter what IO controller card I try with it so there might be a connection. Do you have any idea how to connect a battery to that DS1225Y chip or if it can be replaced with something?

Ok on closer look that is an EISA board (sorry, I missed it first look) so the DS1225Y probably holds the EISA .CFG data. You should be able to get a standard SMC 37C75, 82C765 or equal FDC ISA controller to work to get the floppy working IF you can get into the BIOS. EISA has fall backs that support certain hardware natively, other add-on hardware (video cards, IDE controllers, etc) requires the use of the EISA configs to set IRQ, PORT, etc.
Digikey has replacement 1225Y's but are about $20. The battery is connected same as 1287.
Can you post a picture of the boards bootup screen and first page of the BIOS if you can get in ?

Horun wrote on 2020-10-14, 01:22:

Ok on closer look that is an EISA board (sorry, I missed it first look) so the DS1225Y probably holds the EISA .CFG data. You should be able to get a standard SMC 37C75, 82C765 or equal FDC ISA controller to work to get the floppy working IF you can get into the BIOS. EISA has fall backs that support certain hardware natively, other add-on hardware (video cards, IDE controllers, etc) requires the use of the EISA configs to set IRQ, PORT, etc.
Digikey has replacement 1225Y's but are about $20. The battery is connected same as 1287.
Can you post a picture of the boards bootup screen and first page of the BIOS if you can get in ?

I have not noticed any eisa related issues with the board. I don't have any eisa cards so I have just tested it with isa video cards and standard isa IO cards with winbond or goldstar chips. Hard drives work fine as long as dos is already installed because I can't install it because of floppy drives not working. When I try to read a floppy and use a: and then dir to see directory basically the directory listing is all garbled with random characters and it gets more garbled when I repeat dir command. Just using normal 1.44MB floppies and set the floppy drive type to 1.44MB in bios. There isn't really anything to configure in the eisa utility that is on the hard drive because I don't have any eisa cards. If the battery is not working in DS1225Y it made me wonder if it could be still that it somehow forgets what type of floppy drive is there and perhaps tries to access the drive as if it would be 720KB drive and that would explain the grabled directory listing. This is just guessing from my part because in bios I have clearly set the floppy drive type to 1.44MB

I have one more question. Are DS1225Y and DS1225Y-150+ same chips or at least compatible with each other? I found a place where I could order new DS1225Y-150+ chips.

DS1225Y and DS1225Y-150+ should be compatible. I believe the 150 is access speed of this NVRAM. The speed doesn't really matter and 150ns is the fastest you can get anyway. I've used a -200+ in a similar system without any problems.

Also if you don't use any EISA cards or if you only use EISA cards that are simple devices with no resources to configure (like EISA VGA) then you don't really need to replace the failed DS1225Y. The system should work just fine.

mpe wrote on 2020-10-15, 21:28:

DS1225Y and DS1225Y-150+ should be compatible. I believe the 150 is access speed of this NVRAM. The speed doesn't really matter and 150ns is the fastest you can get anyway. I've used a -200+ in a similar system without any problems.

Also if you don't use any EISA cards or if you only use EISA cards that are simple devices with no resources to configure (like EISA VGA) then you don't really need to replace the failed DS1225Y. The system should work just fine.

If DS1225Y isn't the problem, what could cause the floppy drives not to work with the motherboard?

I'd say no. But these early boards can be complicated and you'll only know for sure once you replace it.

Floppy not working usually suggests some problem with DMA.

Various DOS tools should be able to tell whether your floppy is configured as 1.44M or 720k. Do 720k discs work fine?

mpe wrote on 2020-10-15, 21:51:

I'd say no. But these early boards can be complicated and you'll only know for sure once you replace it.

Floppy not working usually suggests some problem with DMA.

Various DOS tools should be able to tell whether your floppy is configured as 1.44M or 720k. Do 720k discs work fine?

Everything else worked fine except floppy disk drives if I remember correctly. It booted fine from a hard drive that already had dos and all the software I ran from a hard drive worked fine. I couldn't really copy any new software to the hard drive though because of floppy drives not working.

I need to re-test things to make sure. Only 720K disks I own are original games so I don't remember if I tested any of those. I'll reply more later.