@CouryC, Tripelef etc -- On my MK, I can confirm the problem was the power supply as Pasky and some the members point it out... took out the old power supply but there is no way to dial up the power meeting without opening the unit since the meter cable is solder to the old power supply and I do not know how to solder those cable into the new power supply. I got it to 5 volts and that is where it will stay. The MWP606 fit in the case but there is no where to secure it to the metal base of the MK so I'' have to remember to be careful.. Hope that this fixes your issues as well.
I am using this power supply which was recommended by some of the members on the HAS tread - MWP606http://www.ebay.com/itm/360127247409
I am using this cable with the (shield upgrade) recommended by RGB with a Scart switch.http://www.ebay.com/itm/Nintendo-NES-Fa ... Swl8NVdJn9