derek0606 wrote:
What should I do to check my power supply; should I hook up a voltage meter to the connector I was using?
IMHO, PC PSUs are inherently "cheap". I have a 1000W mainframe PSU that produces 150A at 5V, yet still manages to produce stable +/-12V and -5V rails. Each rail is user adjustable by means of externally accessible trimmers, and each rail has a pair of load sense wires that allow the PSU to automatically compensate for IR losses in the cables.
By contrast, a PC PSU is typically a compromise. The rails are not independent. Instead they all are derived from the same secondary winding (except for the +5VSB standby supply). "Regulation" is typically achieved by sensing a weighted average of the heaviest rails, +5V and +12V. This means that, if the +5V rail droops, then the +12V rail rises by about 4 times the amount.
Here is the circuit diagram and description for a typical ATX PSU:
http://pavouk.org/hw/en_atxps.htmlSee the voltage sense resistors R20, R21, R25 and R26. Pin 1 of the PWM controller, TL494, is maintained at 2.5V by feedback action.
The regulation formula is:
5.0V * 3K01/(3K01 + 3K01) = V12 * (3K09||150K||5K6) / (27K + 3K09||150K||5K6) + V5 * (3K09||150K||27K) / (5K6 + 3K09||150K||27K)
This reduces to:
2.50 = V12 * 0.0678 + V5 * 0.327
For this PSU, if the +5V rail increases by 50mV, say, then the +12V rail will fall by 241mV.
This means that a CPU which is powered from the +5V supply will cause the +12V rail to vary significantly in tandem with its own level of activity. I can easily demonstrate this with a CPU cooler such as CPUidle and a hardware monitor such as Motherboard Monitor 5.