Thursday, October 20, 2005
The Search for a Replacement CMOS Battery
This is the kind of thing that keeps me up at night. Seriously!
I can't get stupid things like repairing my old worthless computer out of my head and yet I can't remember to call my neice on her birthday. Ugh
Anyway
Call it an RTC battery, Call it a CMOS battery, If you found this post and don't know me then you are probably pulling your hair our trying to find ways to get an old machine stop giving you a "real-time clock" error. I will use the terms RTC and CMOS battery interchangeably. If you know the difference, please post a comment explaining as much.
The "real-time clock" is a clock kept in your computer's BIOS. It doesn't really have much to do with your operating system, but is kept in memory on your motherboard. The mother (aka "main") board also stores some basic input/output system (BIOS) info that is critical to the operation of your computer.
The issue that arises is that the board needs power independent of the ac power source to store this information. So your computer has a small lithium battery that provides enough juice to the motherboard to retain that info in memory when you turn off or un-plug your computer.
So what happens to a lithium battery after about 10 to 12 years? It dies.
A CMOS bat on an old machine I keep around died, and I had to go about the process of learning how to replace it.
Now, I knew what an RTC battery was, so I knew what to look for and how to start the process of replacing it.
First it is important to note that your operating system will probably never report a CMOS problem. You will see error messages before you get into Windos, Mac OS, or whatever. These pop up on the bios boot screen. You will have seen one if you've every tried to start your PC without a keyboard attached, or started your pc with a "non-system disk" in the floppy drive.
If you get an error message like "RTC is out of sync, CMOS checksum error, or (duh) replace CMOS battery" you might have a need to replace your CMOS battery.
On most recent computers, this is a super easy fix, but it does require you to open the case and not break anything on the inside of your PC. If you aren't comfortable with that, just take you computer to a repair shop. Its pretty much always a good idea to take your laptop to an experienced repairperson, unless you don't care if you break it. Laptops are more difficult to disassemble and repair, but it can be done sucessfully.
So for not-a-laptop, you will want to figure out what kind of motherboard you've got. The link below is a sort of gateway to a gallery of older MoBo's. If you can't ID your MoBo just from looking at it, take a peek at this site and try and find yours by simple recognition.
http://rtgo.hopto.org/th99/
You will also sometimes be able to ID the Motherboard from the information that is displayed on screen when your computer first boots up.
The RTC battery usually looks like a coin and lays horozontally on the MoBo. Sometimes they are suspended on legs but usually they sit in a holder soldered to positive and negative poles on the board. If you see a coin thingy about quarter-sized in a holder, you are in good shape. There should be a way to pop it out and put a new one in. If that is the case, you're set. You'll find a replacement by checking the numbers on the old battery. Find your replacement on-line. Its out there somewhere and that is probably what a repair shop would do anyway.
Occasionally the battery is solderd to the board. This presents a bit more of a problem. If your battery is soldered down and you can't use your computer anymore because of it, consider throwing it in a nearby dumpster. Its probably 10 years old anyway. If you're like me and you just can't part with it yet, you'll have to do a bit more work.
I was personally dealing with an old Packard Bell Legend 10CD. Its a 486 with the PB450 MoBo. My RTC battery was the Rayovac 3V BR1225. It was suspended horozontally above the board and the legs were soldered onto the board.
I found the part (with legs) on-line fairly easily, but I don't have any soldering equipment, so I searched for another solution. After some reading, it became obvious that it didn't matter what battery I used as long as I hooked it up correctly and it produced 3V of output.
Now the makers of this and other old boards were wise enough to give me a way out without any soldering. They left me a 4-pin jumper that works as an input to the CMOS memory. It is there specifically as a way to replace the RTC battery without soldering.
Instead of ordering an expensive (and potentially non-existant) external lithium CMOS battery, and instead of ruining my computer by f'ing up the solder-job. I chose to buy a AAA battery holder from Radio Shack for $1.69. I then took the 4 pin connector of an internal CD audio cable and fastened it onto the positive an negative wires (red = +) coming out of the battery holder.
I checked my MoBo specs and pluged the 3v battery pack (1 AAA battery = 1.5v) up to the board (connecting red to pin 1 is almost always the rule) and to my relief it worked. Now that old 486 turned 586 is working again and it only cost me $1.69 and 2 AAA batteries.
And that is pretty much what I did yesterday.
I can't get stupid things like repairing my old worthless computer out of my head and yet I can't remember to call my neice on her birthday. Ugh
Anyway
Call it an RTC battery, Call it a CMOS battery, If you found this post and don't know me then you are probably pulling your hair our trying to find ways to get an old machine stop giving you a "real-time clock" error. I will use the terms RTC and CMOS battery interchangeably. If you know the difference, please post a comment explaining as much.
The "real-time clock" is a clock kept in your computer's BIOS. It doesn't really have much to do with your operating system, but is kept in memory on your motherboard. The mother (aka "main") board also stores some basic input/output system (BIOS) info that is critical to the operation of your computer.
The issue that arises is that the board needs power independent of the ac power source to store this information. So your computer has a small lithium battery that provides enough juice to the motherboard to retain that info in memory when you turn off or un-plug your computer.
So what happens to a lithium battery after about 10 to 12 years? It dies.
A CMOS bat on an old machine I keep around died, and I had to go about the process of learning how to replace it.
Now, I knew what an RTC battery was, so I knew what to look for and how to start the process of replacing it.
First it is important to note that your operating system will probably never report a CMOS problem. You will see error messages before you get into Windos, Mac OS, or whatever. These pop up on the bios boot screen. You will have seen one if you've every tried to start your PC without a keyboard attached, or started your pc with a "non-system disk" in the floppy drive.
If you get an error message like "RTC is out of sync, CMOS checksum error, or (duh) replace CMOS battery" you might have a need to replace your CMOS battery.
On most recent computers, this is a super easy fix, but it does require you to open the case and not break anything on the inside of your PC. If you aren't comfortable with that, just take you computer to a repair shop. Its pretty much always a good idea to take your laptop to an experienced repairperson, unless you don't care if you break it. Laptops are more difficult to disassemble and repair, but it can be done sucessfully.
So for not-a-laptop, you will want to figure out what kind of motherboard you've got. The link below is a sort of gateway to a gallery of older MoBo's. If you can't ID your MoBo just from looking at it, take a peek at this site and try and find yours by simple recognition.
http://rtgo.hopto.org/th99/
You will also sometimes be able to ID the Motherboard from the information that is displayed on screen when your computer first boots up.
The RTC battery usually looks like a coin and lays horozontally on the MoBo. Sometimes they are suspended on legs but usually they sit in a holder soldered to positive and negative poles on the board. If you see a coin thingy about quarter-sized in a holder, you are in good shape. There should be a way to pop it out and put a new one in. If that is the case, you're set. You'll find a replacement by checking the numbers on the old battery. Find your replacement on-line. Its out there somewhere and that is probably what a repair shop would do anyway.
Occasionally the battery is solderd to the board. This presents a bit more of a problem. If your battery is soldered down and you can't use your computer anymore because of it, consider throwing it in a nearby dumpster. Its probably 10 years old anyway. If you're like me and you just can't part with it yet, you'll have to do a bit more work.
I was personally dealing with an old Packard Bell Legend 10CD. Its a 486 with the PB450 MoBo. My RTC battery was the Rayovac 3V BR1225. It was suspended horozontally above the board and the legs were soldered onto the board.
I found the part (with legs) on-line fairly easily, but I don't have any soldering equipment, so I searched for another solution. After some reading, it became obvious that it didn't matter what battery I used as long as I hooked it up correctly and it produced 3V of output.
Now the makers of this and other old boards were wise enough to give me a way out without any soldering. They left me a 4-pin jumper that works as an input to the CMOS memory. It is there specifically as a way to replace the RTC battery without soldering.
Instead of ordering an expensive (and potentially non-existant) external lithium CMOS battery, and instead of ruining my computer by f'ing up the solder-job. I chose to buy a AAA battery holder from Radio Shack for $1.69. I then took the 4 pin connector of an internal CD audio cable and fastened it onto the positive an negative wires (red = +) coming out of the battery holder.
I checked my MoBo specs and pluged the 3v battery pack (1 AAA battery = 1.5v) up to the board (connecting red to pin 1 is almost always the rule) and to my relief it worked. Now that old 486 turned 586 is working again and it only cost me $1.69 and 2 AAA batteries.
And that is pretty much what I did yesterday.
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