Finally you can see the circuit board for DC power.
Desolder your old DC jack following the This Guide "How To Desolder Components"
"How To Desolder Components"
Another and much better guide to desolder and re-solder a power jack is DC power jack repair guide. Do-it-yourself instructions.
The credit goes to Laptop Freak.
I did not use desoldering pump. Instead, I bought desoldering braid from RadioShack for about $5. Soldering before desoldering works pretty well, though.