Fuses can be checked by using an ohmmeter (aka, multimeter). Place the meter in the lowest OHMS range, connect the leads across the fuse and if it reads 0 ohms, the fuse is good. (NOTE: remove all power from the system before doing this!) The problem is identifying which components on the motherboard are
fuses. If you look closely, you will see part names written in white ink (generally) on the circuit board. Fuses will usually begin with "F" (i.e., F1, F5, F11, etc.). A picture of some fuses from a T22 is here:http://www.kawakami-ca.com/images/t22_main_fuses.jpg
The T61 will use similar looking fuses. That said, your problem may be more serious than a fuse. If the system does not operate with either a known good AC adapter or a battery, then that means two
separate fuses would have to be defective. There's one that protects the DC input jack and another one that protects the battery. This usually means that there's some other power problem on the motherboard. If that's the case, look closely at all of the components to see if you can detect any catastrophic failures like the one circled in this photo:http://www.kawakami-ca.com/ibm_t2x/let.jpg
The other components outlined in blue are also fuses. You should also look for any parts that may have come loose from the board. This could entail removing
the entire motherboard as there's also parts soldered on the back side.