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First ever attempt at repairing a Dalas type RTC battery today. ;)

I did one of these modifications a few days ago to my Compaq Deskpro 386/20e. I only drilled one hole in the side to access the positive battery terminal, and soldered to pin 12 for the negative. I have the CR2032 battery in a case, the wires of which I soldered to those spots. I checked that the battery case polarity matched the contacts on the module. The computer still says that there is no CMOS battery. What did I do wrong? Can I check success with a multimeter? I also have one other 20e that I need to modify once I get this first one corrected.

This is the video I followed.
 
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Bill-kun said:
I did one of these modifications a few days ago to my Compaq Deskpro 386/20e. I only drilled one hole in the side to access the positive battery terminal, and soldered to pin 12 for the negative. I have the CR2032 battery in a case, the wires of which I soldered to those spots. I checked that the battery case polarity matched the contacts on the module. The computer still says that there is no CMOS battery. What did I do wrong? Can I check success with a multimeter? I also have one other 20e that I need to modify once I get this first one corrected.
Click to expand...
This is normally a 2-step process:
1. Disconnect the (faulty/low) internal battery
2. Connect external battery

Did you do step 1 ?
For example, at [here], which covers the DS1287, a break is made in the connection to the internal battery's minus terminal.
 
I’ve had so many headaches and nightmares over the years with destroyed motherboards, I have gotten to the point where I’m actually relieved when I open a machine and find a Dallas chip instead of a leaking or exploded battery.

Sure, a Dallas is somewhat of a pain, but would you rather spend a few minutes carefully cutting that chip open, or spend hours repairing damaged traces on a board that may be too far gone anyway?
 
modem7 said:
This is normally a 2-step process:
1. Disconnect the (faulty/low) internal battery
2. Connect external battery

Did you do step 1 ?
For example, at [here], which covers the DS1287, a break is made in the connection to the internal battery's minus terminal.
Click to expand...
No, I did not disconnect the internal battery. I wanted my first attempt to be the minimum work possible, so that there was the minimum possibility of me screwing it up.

I disconnected the module again in order to redo the soldering. I plugged it back in a booted. The boot screen, before it prompted me for the diagnostic disk, said that the time had been lost and the BIOS settings were not set. Then it prompted me for the diagnostic disk and to press F1.

Previously, the boot screen said that the time had been lost, and prompted me for the diagnostic disk and to press F1. The BIOS did not say that the BIOS settings were not set. So it seems to be getting some amount of power from the battery. After going into the diagnostic, it asked me if I had disconnected the battery since I had last gone into the BIOS. When I said no, it replied that the BIOS had lost power anyway, and to contact the dealer or hardware help person.

Even if I pressed Ctrl-Alt-Del to reboot (keeping the power on), the BIOS still said it lost the clock time, and it still prompted me for the diagnostic disk. But I could choose to not insert the diagnostic disk, but instead a normal boot disk or even boot from the hard drive by pressing F1.

I don't know how, but now after several iterations of rebooting and changing the BIOS settings to what they should be, the clock and BIOS settings are finally sticking now and it's no longer saying I need to set them. (Unless I try tomorrow and I start all over again with it saying the clock is not set and the BIOS settings are not set.)
 
Bill-kun said:
No, I did not disconnect the internal battery. I wanted my first attempt to be the minimum work possible, so that there was the minimum possibility of me screwing it up.
Click to expand...
The minimum work required includes disconnecting the internal battery, otherwise you end up with two batteries in parallel, the bad one at a low voltage, and the good one at a high voltage. (Comparatively speaking.)
The low voltage battery will drag down the voltage on the other battery.
 
I booted up after letting it sit overnight. It kept the time but not the BIOS settings, and reported error 162, system options not set (run set up), insert diagnostic diskette.

I’ll disconnect the original battery and see if that fixes it.
 
I drilled straight through the whole wall above pin 16 to break the negative connection to the original internal battery. I set the correct time and date and other stuff, then turned it off and let it sit overnight. I checked this morning and it had kept the time and all settings.

Easier than I thought.

picard ah ha.jpg
 
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