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Compaq Deskpro 386/25e CMOS battery location?

J

jetmike747

Member
Joined
Apr 3, 2011
Messages
18
Location
NYC, New York
Hey everyone, I'm new to this site, but after much research and not being able to find an answer I thought I'd turn to you guys.

So here's what's going on, I recently picked up a Comaq Deskpro 386/25e from ebay cause it was the first computer I ever used as a kid.

So before it comes I make a DOS 6.22 boot-able floppy and get a hard drive compatible with the system (original was taken out). Long story short, I'm able to boot DOS from my floppy and install DOS and Windows 3.1 on the hard drive.

Now the problem is wen I boot the system I get a:
"162 System Options not set insert diagnostic diskette and press F1 to continue"

After some research I found out this means that CMOS battery is dead. So I go ahead and find the program to make a compaq diagnostic disk (don't ask me how I found it lol) and all goes well, I boot from the disk and go into the BIOS of the machine. Problem is without a good cmos battery the computer won't save the bios settings,and won't "see" the hard drive, therefore I can't boot from it. This is a common problem with old compaqs so I thought I'd just change the CMOS batt and I'll be good to go.

Except I can't find the CMOS battery for the life of me.

I was able to find motherboard diagrams online, and you can see the 386/20e (one model down) has a connector for the battery, but the 25e doesn't.

386/20e http://bk0010.narod.ru/hardware_specs/m/C-D/30869.htm

386/25e http://bk0010.narod.ru/hardware_specs/m/C-D/30868.htm

20e has it in the top left, but I looked at my mobo, and only the speaker connector is present.

Any help would be appreciated, I've been pretty frustrated with this and found myself looking inside the computer for a good 15min and couldn't find it :mad: lol.

Thanks for looking!
 
The 386-25e shows a Real Time Clock (RTC) module, lower left on the diagram. So, you don't have a battery. You have a RTC to deal with. You will need to replace the RTC or search this site for instructions on how to "carve" into the old RTC and apply an external battery. Average price for a new Dallas RTC is about $20-$25 on eBay. However, if you have access to a Dremel kit and are able to use a soldeing iron you can easily fix it yourself.
 
I was wondering what the real time clock module was, but when I saw it was on the 20e motherboard also I figured it was something different. If the 25e doesn't have a battery, but instead a RTC, how come the 20e has both? Sorry if it's a dumb question, I'm new to this stuff.

Quick search on the internet and found this:

http://www.kahlon.com/itemdetailpg.asp?itemid=931883

Could the clock and the battery be one unit on the 25e?
 
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jetmike747 said:
I was wondering what the real time clock module was, but when I saw it was on the 20e motherboard also I figured it was something different. If the 25e doesn't have a battery, but instead a RTC, how come the 20e has both? Sorry if it's a dumb question, I'm new to this stuff.

Quick search on the internet and found this:

http://www.kahlon.com/itemdetailpg.asp?itemid=931883


Could the clock and the battery be one unit on the 25e?
Click to expand...

Good question but I don't think so. I not an expert on the Comp, but I would have to say its just the nature of the beast. The last 386 that I had was a clone (long, long ago) and it had a small riser on the mobo to attach 2 'AA' batteries. Point is, it wasn't marked or in the manual. So, you may want to go over that board real good and make sure that you're not missing something that may not be documented. Just a long shot but worth the effort. The reason your other mobo has both is to enable to save your BIOS settings. The 25 mobo has all settings programed into the BIOS.

Here's a link from a forum member: http://www.vintagecomputer.net/cisc367/386-486-era_APlus.pdf
 
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The real-time clock originally used a Motorola MC146818 IC (why it's called "CMOS" is beyond me--there are other CMOS devices on board), which required an external battery (and crystal). So motherboards had an external battery header. The Dallas (or compatible) RTC modules basically took the 146818, bent some pins up and attached a lithium cell and a crystal and potted the whole mess in a block of epoxy. Some motherboards had both an external battery header as well as an on-the-motherboard NiCd or lithium coin cell.

Later motherboards skipped the crystal and battery header (or on-the-motherboard battery) and used the DS1287 module directly instead. It was an effective cost-cutting move and guaranteed at least 7 years of operation before the RTC module's battery failed.

What this means is that if you have a battery header (and 32KHz crystal) on your motherboard, you can substitute a MC146818 for the module and hook up an external battery. If you don't have a battery header and just an RTC module, you either need to replace it or do some surgery on it to add a replacement cell.
 
I have A Deskpro 386/20e and it uses a Dallas 1287 or 12887 RTC. Yes, the battery is encapsulated in the RTC. If your uses the same RTC, you will have to remove the drive bay that holds the floppy and hard drives to get at it.

It's also possible to use a Dallas DS12885. It allows the use of an external battery, but you have to bend up some pins and add the wires for the battery and an external oscillator.

I tried to modify a DS1287 but was unsuccessful and wound up damaging the thing.
 
Thanks for all the input every body! I've learned a lot from all of you and truly appreciate it.

So I now know that my RTC has a clock crystal and battery in one. I found this online:

http://www.kahlon.com/itemdetailpg.asp?itemid=931883

looks to be like a direct replacement. My only question is, is the RTC module soldered directly to the motherboard or in a socket? Cause if it is on the mobo (like the 386 portable), it's going to be a pain replace it if I buy one from the link above. Chuckster if you could remember if it is or not, it would help greatly, I just setup the computer nicely and don't want to take it out and apart to look at it.

I don't think I could find myself soldering on a old computer board cause of the fear of breaking it. The computer means a lot to me, and it took me a while to get it. If it's directly soldered on it looks like I'm going to have to just boot DOS from the floppy and access my hard drive from there, although I'd love to have the machine working like it did when I was a kid.

Once again everybody thanks for the input and reading my post!
 
Hey druid sorry didn't see your post while I was writing. That looks to be much cheaper from the link I found lol thanks for that. Now all I need to know is if it needs to be soldered on or not, cause if it does, I'm trouble!
 
jetmike747 said:
Hey druid sorry didn't see your post while I was writing. That looks to be much cheaper from the link I found lol thanks for that. Now all I need to know is if it needs to be soldered on or not, cause if it does, I'm trouble!
Click to expand...

Not a problem. I know what you mean though, I had to replace the modules in both the Commodore PC20-IIIs I have and it involved removing EVERYTHING in the box to get to it. Even if it had been in a socket it was under the drive stack and you couldn't get at it without removing all the drives. I removed the old one and put a socket in so, at least, whomever bought it wouldn't have to take the whole damn motherboard out to replace it.
 
Druid6900 said:
Not a problem. I know what you mean though, I had to replace the modules in both the Commodore PC20-IIIs I have and it involved removing EVERYTHING in the box to get to it. Even if it had been in a socket it was under the drive stack and you couldn't get at it without removing all the drives. I removed the old one and put a socket in so, at least, whomever bought it wouldn't have to take the whole damn motherboard out to replace it.
Click to expand...

Damn. That's nuts, especially having to take everything out. At least you put the socket in for next time. I mean I have done soldering in the past and I'm pretty comfortable with doing basic things, but soldering on a module with a lot of pins on an old motherboard of a computer I tried really hard to find in good working condition I'm not too comfortable with lol. So I'm hoping, really hoping it's in a socket.
 
jetmike747 said:
Damn. That's nuts, especially having to take everything out. At least you put the socket in for next time. I mean I have done soldering in the past and I'm pretty comfortable with doing basic things, but soldering on a module with a lot of pins on an old motherboard of a computer I tried really hard to find in good working condition I'm not too comfortable with lol. So I'm hoping, really hoping it's in a socket.
Click to expand...

Well, if it's not, there are people on here that are qualified to remove the RTC, install a socket, put the new RTC in and test it for you for a reasonable rate.
 
Well, if it's not, there are people on here that are qualified to remove the RTC, install a socket, put the new RTC in and test it for you for a reasonable rate.
Click to expand...

Thanks druid, I'll keep that in mind if I ever need work done to it in the future!

It's in a socket.
Click to expand...

Thanks chuckster, hearing that just made my day. I ordered the module from the site druid suggested, and I'll keep you guys updated on how the install goes. How long do you think this module will last for? I may just order another so I can keep this machine going and save it for my kid one day like my dad did for me lol. Will the battery die if it's not inserted in a machine?
 
Well, according to the specs on the 1287, it has a shelf life of about 10 years and an operational life of between 5 and 7 years. The 12887 does a bit better than this, I believe, but, check back with me in 7 or 8 years and I'll let you know if the ones I've used are still working LOL. Your Mileage May Vary :)
 
Well, according to the specs on the 1287, it has a shelf life of about 10 years and an operational life of between 5 and 7 years. The 12887 does a bit better than this, I believe, but, check back with me in 7 or 8 years and I'll let you know if the ones I've used are still working LOL. Your Mileage May Vary
Click to expand...

Haha that sounds like a plan druid. Well I may just order the second one, and modifiy it to someday to hook up an external battery to it like a member here did. But thanks again everyone for all your help, because of you guys, another vintage computer lives on! :D lol. I'll keep you guys updated with how the installation goes.
 
jetmike747 said:
Well I may just order the second one, and modifiy it to someday to hook up an external battery to it like a member here did.
Click to expand...

If you are going to keep it around for a while, store the second 12887 in the freezer and the internal battery will stay fresh and the "count-down" won't start until it thaws.

And, yes, I'm serious.
 
Druid6900 said:
If you are going to keep it around for a while, store the second 12887 in the freezer and the internal battery will stay fresh and the "count-down" won't start until it thaws.

And, yes, I'm serious.
Click to expand...

hey sorry about the delay druid, haven't been on in a few days, but I have to admit, that makes complete sense lol slowing down the reaction inside the battery by reducing the temp by putting it inside the freezer....brilliant lol

looks like im gunna have to clear a little bit of space in my freezer for an RTC lol :D

you don't think the cold could have any effect on the rest of the chip?
 
jetmike747 said:
you don't think the cold could have any effect on the rest of the chip?
Click to expand...

Well your car sits out in sub-zero weather (probably colder than a freezer) and your radio doesn't crap out or your electronic ignition or {fill in other electronic parts in your car}.

I'm pretty sure it'll be fine when you finally take it out and warm it up in the microwave :)
 
Druid6900 said:
Well your car sits out in sub-zero weather (probably colder than a freezer) and your radio doesn't crap out or your electronic ignition or {fill in other electronic parts in your car}.

I'm pretty sure it'll be fine when you finally take it out and warm it up in the microwave :)
Click to expand...

Guess you got a point there :D. Or when you see those insane overclocking vids with liquid nitrogen/helium cooling. I think it'll be just fine lol
 
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