Our Tektronix 2402A GPIB controller would not boot. The BIOS uses a Dallas DS1287 RTC which has an internal battery which was dead. The BIOS defaults are not correct for operation and upon exiting the BIOS settings the system reboots, so it checks and determines that the battery is dead and again loads the defaults. I found an excellent repair page for the Dallas DS1287 (external site).

I found it easiest to cut into the sides of the module with an X-Acto knife and then scrape down to the pins with a small screwdriver. You can use the X-Acto knife to cut under the ground pin to separate the battery and solder new wires onto the pins. I used a 3V coin cell that I mounted on top of a pair of unused ROM sockets.