I asked my technicain guy to mend a switched mode power supply today where a resistor had burnt out going open circuit because somebody abbused it trying to do stuff it wasnt meant to do.It was quite funny because he took the old resistor out,out a new one in,soldered one end then the other and promptly gave himself a shock as the power supply started up again using the charge in the resevoir capacitors,still we live and learn,its a good job it wasnt an invertor or he might not have learnt from his mistake.