I think I have a bad PCpower supply. It turns on and runs but the
attached motherboard will not operate.
After testing some other known-to-work power supplies, I think that
the power good line on the supply in question is not working. Other
working supplies put out +5VDC on this line while this supply puts out
nearly nothing.
I just need to confirm that +5VDC is what should appear on the power
good line. Googling around hasn't provided any good info on this.
Voltage on Power Good must exceed 2.4 volts. Significant also is that
number to three digits. If this does not occur, typically voltages on
any orange, red, or yellow wire is defective. Green wire orders power
supply on. Supply has about 2 seconds to measure orange, red, and
yellow voltages. If OK, gray (Power Good) wire goes to less than 0.8
to well above 2.4 volts
Now, if power supply controller does not see power good, then power
supply controller will turn off power supply. So, first see what one
of orange, red, yellow, and purple wires do both before and when power
switch is pressed. Purple should remain above 4.87 at all times (and
also related to number on Power Good wire). Other voltages should
rise from zero until power supply controller cuts them off. Any one
voltage that does not increase as the power switch is pressed implies
where to look for the problem.
Other possibility is that a failure exists in the power supply
controller or Power Good driver is defective. With power supply
disconnected from motherboard, connect the meter in DC volts, shunt a
paper clip from green wire to black wire, then record that voltage.
Repeat same experiment with meter in Ampere mode between that Gray
(Power Good) wire and any black (ground wire). When a paper clip
connects green wire to black wire, then current on Power Good should
significantly exceed 0.02 amperes (20 mA). Set meter to highest
current. Short the green wire (Power On#) to ground, then slowly
decrease meter scale until a useful current number is read.
That Power Good wire must output more than 2.4 volts and 0.02
amperes. Those numbers will report things significant. And then post
those numbers here to learn other facts. Those numbers may be
reporting more than you realize.
