mpc 500 power supply issues!!!!

hey guys i bought a used mpc 500 from this guy and its having some power supply issues. whenever i plug the power supply to a wall outlet, and take out the batteries, it doesnt work. can it be the powersupply is faulty?

yo, i had this problem, i noticed my batteries kept dieing while plugged it, what i did to trouble shoot is pushed the status button, it tells you weather you are running on battery, or plug, if you are plugged in it will say 12.00v, so push the status button, and move the wire around, or try different outlets, when i was moving my plug wire around i noticed a nick in the wire right by the plug box, so i had to pry the box apart, splice the wires and fix it,. now my plug looks hella gehto, but it works...

ok cool thanx man. ill look into it. hey do you know of a good mini synth that goes well with the mpc 500 but under 150 dollars?