Yeah, sorry about that. This is only my 2nd computer to build and I've
never had a problem like this.
All that 'try this and try that' could have been identified in less
than two minutes with a 3.5 digit multimeter - a $20 tool sold in most
every 'guys' store - and sometimes sold on sale for only $10. .
In your case, voltage on the purple wire (from power supply to
motherboard) is t measured when power cord is connected (and power
switch not pressed). That should measure more than 4.87 volts DC.
Next is green wire that must be more than 2 volts before power switch
is pressed AND less than 0.8 volts when switch is pressed.
Green wire will probably be first indication of trouble. Assuming
the green wire has not shorted to something else inside the power
supply, then power supply is not defective. Later we can confirm this
if (when) power supply is removed.
Lastly, measure voltage between two wires from power switch. This
should be well about 2.4 volts when switch is not pressed and drop to
near zero when switch is pressed. If yes, then we have traced the
problem directly to power supply controller on motherboard.
OK. Previously noted was that green wire inside that power supply
could have shorted - therefore override the power supply controller.
Lastly we verify this rare problem does not exist. Disconnect AC
power cord. Power supply disconnected from motherboard and meter put
into current measurement maybe at 2 amps DC. Now connect power supply
again to AC receptacle. Put meter probes from green wire to any black
wire. Power supply fan may start running. Switch meter to lower
current ranges until a current is measured. This green wire current
must measure less than 0.01 amps or 10 milliamps. If so, then problem
is definitely in power supply controller. If that green wire current
is significantly more than 10 ma, then something inside power supply
has shorted.
Since inputs to motherboard controller are OK (power switch wires
and purple wire), and since green wire current is not excessive, then
motherboard controller must be the problem. We have followed the
evidence to identify a defect. Now inspect power supply controller
area of motherboard for a physical problem (ie standoff shorted to PC
trace, a crack, or a bulging capacitor). However most all problems
leave no visible indication.
In maybe two minutes using the meter, a suspect is identified
without wasting all that time and money swapping parts.
Meanwhile, numbers from meter readings may provide other useful
information when posted - making replies also more useful.
