well there are many different styles of voltage regulators. there are simple ones consisting of just resistors or a series of diodes keeping a certain voltage in check. there are also electromechanical or coil voltage regulators which are large wraps of wire making a coil turning it into an electromagnet which then dissipates the power. then there are filters which sounds like what you are talking about. inside of a filtered circuit there are resistors and there are also capictors and inductors. the capacitors and inductors either work as an open circuit when they reach the desired voltage meaning they send no power through or they can work like a dead short at a certain voltage. in ac circuits these filters control frequency and also control the voltage and current. in dc circuits they only control voltage and current. so if any of those components go bad they will not work right. i would have to see a schematic of your circuit or the actual circuit board to tell you what might have went bad. oh and i am an electronic engineer lol