About DC Supply Voltage
If you repair any electronic circuit board and found that the supply voltage is lower than usual then there are two possible causes. If the supply line is 12 volt but you only got 8 volt at the vcc pin of an IC, you will know that it is either the IC itself have problem or the supply line can’t sustain itself when there is a current draw. To confirm which one is the cause, just touch on the IC to check if it too hot to be touched or not. If it is very hot you know that it is indeed the IC itself that have drained the extra current causing the supply voltage to drop. If the IC remain cold then the problem is in the components along the supply line. It could be a bad filter cap (that have high ESR) ,leaky diode and etc.
If the supply is coming from a voltage regulator IC like 7812/7805 then there is also a possibility this IC could breakdown when under load.