a voltage reading from a pin[test point] in a power supply board that is lower than the marked value usually indicates a bad capacitor. this capacitor is connected between the pin and common ground[-],usually electrolytic. try replacing this capacitor with the same capacitance and voltage ratings.
replace the power supply unit. this should be an easy job because the psu uses plugs that are simply inserted in and out.the plugs and sockets are also clearly marked corresponding to each other.replacement psu are quiet inexpensive and easy to obtain .