That laptop, I believe it's built into the motherboard. There is a seperate board that comes off the motherboard that connects to the battery, but do not mistake that for having anything to do with the DC-DC circuitry. It's just serving to connect the battery to the motherboard (and i believe that daughterboard also has your CMOS battery, your card reader, and a USB port).
One thing that I just remembered (that might not apply to your particular problem) is that I saw a few Thinkpads back in the day that you had to clear their CMOS settings by pulling the battery to get them to charge a battery. I dont know why, and it probably doesn't apply to your case, but it never hurts to try.
But if all else fails, and your're sure your adapter is good, hit up eBay for a board.