In order to get to the DC jack, you must take the motherboard out, and in order to take the motherboard out, you must completely disassemble the entire laptop and take all the parts out one by one.
The following disassembly instructions should apply to all KDS Valiants and most other KDS laptops, because they are very similar inside.
STEP 1: Remove the battery.
STEP 2: Remove the hinge covers and the power button panel. The hinge covers simply slide out.
STEP 3: Remove the keyboard. The keyboard is held in place with two screws and a cable.
STEP 4: Remove the screen. You have to take the screen apart. It's made of two plastic covers. And the screws are hidden between the two. Unplug the cable from the laptop, and unscrew those 4 or 6 screws that hold the screen in an upright position. Then you can take a small piece of tape and stick the screws to your screen's frame, so you don't lose them. Put the screen aside, and let's dig in.
STEP 5: Remove the hard drive. The hard drive is held in place with three screws. When you unscrew them, just lift the hard drive. The hard drive is connected to the motherboard with pins that stick out of the bottom of the hard drive near the screws. Try not to touch the pins and the metal surfaces on the motherboard. If a little dirt or grease gets on the connection between the hard drive and the motherboard, then your laptop won't start up. Store the hard drive on a hard, flat, clean surface far away from magnets and loud speakers.
STEP 6: Take the case apart. The KDS laptop case is made of two parts. All the electric components are screwed to the bottom part. If all 12 screws are removed on the bottom of the laptop (outside), then the top part simply lifts up. Tilt it and unplug the cables. You have to unplug the speakers first. Then unplug the mouse pad. And then lift the top cover all the way. If it doesn't want to come off, look for more screws... Maybe you did not unscrew all of them. There are two tiny screws in the battery compartment which won't let you separate the top. You'll have to use a really small screw driver to unscrew those. (You may want to get a small tape and stick the screws to the laptop case on the outside, so they won't roll all over the table and you won't lose them.)
STEP 7: Remove the electric board that has the power switch. (It's the one sitting on top of the CD drive.) This part is fastened to the case with two black screws. Lift it UP. It may be a little bit hard to lift, because as you lift it, it disconnects from the motherboard.
STEP 8: Remove the floppy drive. The floppy drive is held in place with one black screw. Disconnect the floppy drive's cable and then pull the floppy drive in while you lift it gently. Put the black screw back into the hole where it was.
STEP 9: Remove the small electric board which lies between the floppy drive and the battery. It's held on to the case by two black screws. You already unscrewed one of them when you removed the floppy drive. After you unscrew the other one as well, pull the board upward. Again, it may be a little bit hard to pull. As you pull it, it disconnects from the motherboard.
As you take parts out of the laptop one by one, place them upright on a big flat surface. Make sure that no screws fall out.
STEP 10: Unscrew the CPU cooler. It's fastened to the motherboard with four shiny screws. Don't remove the screws, just unscrew them.
STEP 11: Unscrew the CD-ROM drive. Look for three black screws that hold the CD drive in place. Don't remove the screws. Just unscrew them.
STEP 12: Remove the motherboard from the laptop case. Lift the motherboard in the middle tilting it and then pull it out.
STEP 13: The CPU cooler and the fan is located under that big shiny metal piece. It's pinned down with four long screws. Just lift up the cooler and unplug the fan from the motherboard. This will reveal the CPU. (KDS laptops used single-core 800MHz Intel Pentium III processors. This was the latest technology in 1999, but today it's extremely old and outdated.)
STEP 14: Remove the CD drive. The CD drive is pinned down with three black screws--two long black screws and a short one which is hidden.
STEP 15: Once the three screws are removed, the CD-ROM and its frame slide out.
STEP 16: You can now replace the DC jack!
For assembly, just follow these same instructions going backwards.