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CMOS battery mystery

A

Amigaz

Experienced Member
Joined
Jan 31, 2008
Messages
426
Location
Stockholm, Sweden
Recently got hold of a Commodore desktop pc with a 386DX 33mhz motherboard with symphony chipset made my Peacock
The weird thing is that it has a system clock but there's no place on the motherboard for a battery :confused:
The Ami bios complain that the CMOS battery is low and it refuses to save my bios settings even though I do a warm reboot, can anyone please solve this mystery

Here's some pics of the motherboard, there's no pins for an external battery either

boardwu7.jpg


Here's the clock circuits

clockff4.jpg
 
You see that black rectangle marked "Dallas" next to the AMI BIOS? That's your CMOS, RTC and battery all built into one.

It's not socketed, so, what you'd have to do is unsolder it, put in a socket and replace it with a DS12887 unit or, if you're a masochist, you could do the external coin battery mod to it. There is a link in one of the threads, just search for DS1287 and you'll probably find it
 
Druid6900 said:
You see that black rectangle marked "Dallas" next to the AMI BIOS? That's your CMOS, RTC and battery all built into one.

It's not socketed, so, what you'd have to do is unsolder it, put in a socket and replace it with a DS12887 unit or, if you're a masochist, you could do the external coin battery mod to it. There is a link in one of the threads, just search for DS1287 and you'll probably find it
Click to expand...

Damn, talk about cheap design

Solder? my solder skills go as far as replacing a CMOS battery :(
 
Where are you located? If near to someone with good solder skills, you could be in business. If you get the board to me in NJ, I've made this mod several times.
 
kb2syd said:
Where are you located? If near to someone with good solder skills, you could be in business. If you get the board to me in NJ, I've made this mod several times.
Click to expand...

Would appreciate your help but there's a small catch...I'm located in the country with lots of Volvo, Saab cars and Ikea furniture :razz:
 
Amigaz said:
So there's lots of those things I mentioned in sunny California? ;)

I thought my hints would lead you to Sweden where I'm located :cool:
Click to expand...

It kind of did!

If you do get your "dremel" or dentist's drill out, there is a slightly reduced modification to the 1287 I've got away with.
You only need to get to (and separate) the positive terminal of the internal battery ( grind away about 5mm above pin 20) when the bent-up pin is revealed work up & down it until you have an area big enough to solder to, then grind through the highest point to separate the piggybacked lithium battery. Just connect a wire, check with a meter that there are no volts on the wire relative to 0V (i.e. the battery really is disconnected) & if all OK, connect your new battery to that, and any handy 0V on the motherboard. You can solder a lithium coin cell holder (NOT the cell!) to a handy bit of ground plane.

The original mod mentioned elsewhere involves getting to both battery connections, this saves a bit of work & upps the chances of getting it right by 75%!

If you're not handy with a soldering iron, take it to someone who is!
 
If you decide to take the route of replacing the DS1287 (you find someone with soldering skills), note the following, which is based on previous threads in these forums.

1. The DS1287 and equivalents have a manufacturer specified shelf life of around 10 years.

2. If you source an unused DS1287, the battery within it is either dead, or close to it (because they were made so long ago).

3. If you source a device claiming to be a direct equivalent for the DS1287 (e.g. DS12887, BQ3287):
* Depending on date of manufacture, the battery within it is either dead, or partially depleted.
* As stated by the manufacturer, under some circumstances the device is not a direct replacement.

4. Also, the DS1287 (or equivalent) bought off-the-shelf will be empty of data. The BIOS on some motherboards require that the device be preset with certain data before it is fitted to the motherboard. I think that will be a rare situation.

If you want to read the detail, see thread http://www.vintage-computer.com/vcforum/showthread.php?t=7048

That all sounds negative, but based on the "DS1287" threads you'll find in these forums, there's a good chance that you will able to obtain an equivalent to the DS1287 with some life left in it, and it will work in your motherboard.

Personally, if I had a board with a dud DS1287, I'd be doing the modification where a battery and battery holder end up on top of the DS1287.
 
Based on my experience with the three DS12887s I bought from an outfit in Texas, I believe, when tested with a load battery tester, all three registered a full charge.

Two of them went into Commodore PC-20s and the third went into an IBM PS/2. The IBM required that a jumper be inverted and it worked fine after that. The two in the Commodores worked fine right off the bat and all three are still working fine.

Two 1287s that I pulled off a couple of 386 motherboards that weren't worth repairing (which, of course, I got AFTER I had received the 12887s) show a loaded voltage .2V down from a full charge.

YMMV
 
The DS1287 was made by Dallas Semiconductor, and that company was bought by Maxim. Maxim have an application note at http://www.maxim-ic.com/appnotes.cfm/an_pk/505 which discusses Lithium coin-cell battery life in products such as the DS12887.

In reference to using battery voltage as an indication of remaining charge, the note contains, "The voltage also remains stable during the battery discharge (Figure 2), so the voltage at the end of life is nearly the same as with a fresh battery. While a flat discharge curve is desirable for backup supply voltage, it does make predicting the remaining electrical capacity difficult."

And the "flat discharge curve" of the Lithium coin-cell battery is mentioned at various web sites.

Interesting application note. The only internal deterioration component they've included in the calculations is 'electrolyte evaporation'. So in Case I, they are indicating that because of electrolyte evaporation, if you keep a BR1632 coin cell at 25 degrees C, it will last 230 years, however, because in this case 1.2uA is being always being externally drawn, the life is reduced from 230 to 10.9 years. Hmmm. So an unused BR1632 put on the shelf and kept at 25 degrees C will still be usable in 200 years time!
Why aren't they factoring in self-discharge (loss because of internal resistance), which is what I presume is why various web sites state that Lithium coin-cell battery shelf life is approximately 10 years. Even some of the Lithium CR2032 batteries I have, have "Best before 2016" printed on the packet.
 
Today I got a full AT 386 @33mhz mobo I have bought....guess what...it has that darn Dallas clock/batt chip too...DOH!:hammer:

p1010364rv0.jpg


The little bugger:

p1010366el8.jpg


Have a friend at work who has solder skills...might bribe him to desolder the old chips and solder on the replacements you guys mention?

Thanks for all the advice and tips

btw. this full AT board is huge! can't have been cheap back in the late 80's when I think it was made....have a nice Targa full tower which will be it's new home as a vintage gaming rig for late 80's/early 90's games :)
 
But think of the alternative, one of those onboard ni-cad batteries
that has leaked acid all over the board and destroyed it :D


Amigaz said:
Today I got a full AT 386 @33mhz mobo I have bought....guess what...it has that darn Dallas clock/batt chip too...DOH!:hammer:
Click to expand...
 
mikey99 said:
But think of the alternative, one of those onboard ni-cad batteries
that has leaked acid all over the board and destroyed it :D
Click to expand...


Yeah, you're right....that's the Amiga disease, they must have chosen a battery manafacturer with the leakiest batteries

I could live with a dead Dallas clock circuit battery and just change the bios settings after a cold boot but when this crap circuit can't keep my settings after i warm reboot it's very annoying :rolleyes:
 
Update:

Have tested the huge full AT 386 motherboard which seem to work flawlessly but as I suspected the Dallas chip battery is dead
There's a 4 pin header as you can see on the top left on the motherboard...right over the com port heards, wonder if that's an external battery header? not sure if suck a thing exists on a motherboard when you have a Dallas chip..
Haven't found any any information of jumper settings on this beast...on neither Stason.org or any Total Hardware '99 mirro r :(
 
Many old PC's have the DS1287 in them, many were socketed. I reckon that's something to look for when considering a purchase. The DS1287 is in all the mid-90s Gateway computers I have. Some time back I snagged about 20 of the DS1287s and use them as replacements for the ones that are flat when purchaed. They are all goood pulls from previous computers and I have yet to find a bad one.
You know upon reflection those may indeed be socketed. It's hard to tell by looking as the DS1287 is wider than the socket. I remember thinking the same thing as when I went to pull the first one it was very stubborn.
I have also heard the degradation takes 10-16 years when the battery is on the shelf. Time will tell.
The Northgate 386 SuperMicro board uses the DS1287 and also shows a battery connector @ J1, also a 4-pin header, but I'm not sure how it would be utilized or if it even can be.
Hmm, my 286 showed low battery state the last time I turned it on. It has the the barrrel shaped lithium battery soldered to the board. I better yank that sucker before it starts leaking on me.
 
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