Friday, 5 August 2016
Dallas DS12887A NVRAM PC CMOS External Battery Hack
If you have ever dealt with vintage electronics you'll know the feeling when you see a self-contained NVRAM battery module installed into whatever it is. Is the internal battery exhausted? Will the device still operate without it even if it's replaced?
Well this time it was the turn of a Shuttle HOT-433 motherboard dating from around 1997 and it featured a Dallas DS12887A RTC and NVRAM module. Thankfully being a PC motherboard they are tolerant of a battery failure so i should be able to replace the module and we'll be up and running again.
But then i thought, i know these Dallas RTCs have been hacked open before to gain access to the internal battery so i thought i'd give this one a go and see if i could get the board back up and running without waiting for a new DS12887A to arrive in the post.
So the first procedure was to desolder it and prepare it for surgery, here it is inserted into a IC socket to protect the pins and i have already begun to file down the top of the case to find the battery.
After more filing i eventually revealed one of the battery terminals.
At this stage i also noticed a second terminal just showing through the potting compound circled here in green. Measuring across the large terminal and this small terminal i found 1.2v of a very flat 3v lithium cell.
The next step i broke off the two small welds that attach the large negative battery terminal to break the connection to the internal battery, allowing me to wire in a new connection to an external CR2032 battery clip.
After this was done i installed a socket to the motherboard to allow easy future replacement of the DS12887A RTC.
Once installed the motherboard of course required me to reset the clock and CMOS settings and now the motherboard is working perfectly again.
One that was done and everything proved to be working i applied hot-glue to protect the wires and we're done!