This sounds like typical power supply problems. these units have a stand-by power thats always active;even when unit is off. this allows the settings to be remembered by the u-con. (microprocessor) when you unplug the unit it will reset to factory default, thus erasing faulty power-supply data from improper voltages.(usually low readings) swollen capacitors on power-pcb will effect operation. recommend replacement of all electrolytic caps on power board. even smd's (surface-mounted-devices) can be leaky. they can be checked in circuit with an ESR meter. this is an analog sweep meter (needle gauge, not digital) that can detect faulty, leaky capacitors.