• Please review our updated Terms and Rules here

Compaq Portable III CMOS battery replacement

N

NTICompass

Member
Joined
Aug 4, 2021
Messages
21
Location
Rochester, NY
I have a Compaq Portable III (286), just like in this thread, and it needs a new CMOS battery. My motherboard does not have a DS1287 chip, it just has the LTC-7P-MP-F-S2 battery.

The LTC-7P-MP-F-S2 battery is no longer available, and I don't know what a good replacement is. Here is a picture of it (not mine, but the same): https://mobile.twitter.com/Foone/status/1416175186055864321

It's a 3.4V battery, with 4 legs. Why does it have 4 legs? Can I just replace it with a CR2032 or something? I assume I can use 3.6V or even 3V without issue... right? Which of the 2 pins on the board would I need to use? Is there another viable replacement?

EDIT: Found another thread with a possible solution: https://www.vcfed.org/forum/forum/ge...120#post887120 Looks like you can just throw on a 3.6V battery! Also it shows where to attach the wires!

EDIT 2: Do I need a 3.4V or 3.6V battery? Or can I use a "normal" 3V CR2032? What would be the easiest battery holder to add to this system?
 
Last edited:
I see a chip labeled "CDP6818E", looking this up it seems to be the RTC/CMOS chip. So, I could replace this with a DS1287?

I'm honestly not the best at soldering/de-soldering, so personally I think soldering 2 wires to add a new 3.6v battery would be easier for me than to de-solder the 24pin chip and solder in a socket.
 
Yup, that's the one--just the Harris version of the Motorola original. I was presenting the DS1287 as an alternative if you didn't like the idea of external batteries. But if the RTC is soldered in and not already in a socket, it's not worth the trouble.
 
Now that I think about it, replacing the RTC with a DS1287 (can I use a DS12887 or do I need to "battery mod" an DS1287?) may be "cleaner" than attaching an external battery. I have a friend who could do the (de-)soldering work if needed (I'm not sure if it's socked already, I don't think so, but I'll need to check).

I just want the CMOS setting to be able to save. Currently, I need to boot up the diagnostic/setup disk every time I want to use the machine, it won't boot correctly until I reset/save the CMOS settings.

Thanks for the advice! I'll have to decide on a path to progress on here :)
 
I actually got this working! I decided the easiest route would be to use a 3.6v battery. So, I got one of these: https://www.ebay.com/itm/393034276229

Then I took some pin headers and was able to stick them in the holes where the battery originally was and just hot glued them in, didn't need to solder. Using some jumper wires, I was able to stash the battery under the board where the drives are and connect the wires. Now the CMOS settings actually save!!!

Here's a picture from another thread where to hook up the battery: https://www.vcfed.org/forum/filedata/fetch?id=1032331&d=1571819513 (Yes, it works with only these 2 pins, the other 2 are not connected).
 
You must log in or register to reply here.
Back
Top