Picked up the meter in Kmart.
Here's the results, machine off, after using shutdown in windows:
purple 5, green 5 grey 0
I waited 5 minutes and without touching any buttons, tested again,
purple 5, green 5, grey 0
Pressed the front power switch, green power LED lights but
machine does not power on. Got these voltages as fast as I could
(within about 30 seconds anyway)
purple 5, green 4.9 grey 0
I'm not sure if I full understood your instructions regarding the
"when" to test- if I should do more, please let me know.
Likewise, if you see a glaring problem already.
A meter should be reporting at least three digits. Reason why an
analog meter is insufficient: we need more than one digit. If only
one digit displayed, then the meter switch should be switched to 20
volt DC range. 0 could be OK or too high. Is zero 0.2, 0.6, or 0.75?
Assuming those numbers are 5.00, 4.90, 0.00, etc: When power switch
is pressed, then power supply controller should drop green wire
voltage to near zero (well below 0.80 volts). Power supply controller
is not telling power supply to power on if voltage remains well above
2 volts.
Power supply controller has to inputs: power switch and purple
wire. Purple wire remaining at 5.00 volts is OK. Now connect meter
to two points where power switch connects to motherboard. Voltage
between those two points should measure something less than 5.00
volts. When switch is pressed, then that voltage should drop to zero
(well less than 0.80 volts). If yes, then other power supply
controller is getting good inputs. We move on.
If both power supply controller inputs are OK, then power supply
controller is somehow defective OR something inside power supply is
creating so much current as to hinder (overwhelm) the controller's
'Power On' request. Final test is to use meter in current mode. This
typically means moving a lead from the Volt-Ohm hole to the Ampere
hole; and setting meter in a maximum current range (2 amps?).
Remove AC power cord. Then disconnect that 20 something pin
connector and other power connector (near CPU) from motherboard.
Attach meter leads to green and any black wire. Restore AC power to
power supply. Power supply will probably power on fans, disk drive,
etc
Now slowly reduce meter range switch so that zero increases to a
useful multidigit number. If that current is less than 0.01 amperes
(10 milliamps), then power supply is not overwhelming power supply
controller output - a good condition. Therefore problem is isolated
to the power supply controller located on motherboard.
Sidenote. Note when purple wire is and is not at 5 volts. Only
time you can add or remove hardware is when purple wire is zero
volts. That means removing power cord from power supply or AC wall
receptacle every time before making any changes. When power cord is
restored, then safety circuits on power supply controller are reset.
IOW if green wire responds to power switch right after power cord is
reconnected, then one possible suspect is the 'reset' safety lockout
circuit inside power supply controller. Removing and reconnecting
power cord resets that safety lockout circuit.
Learn what does and does not permit power switch to cause green wire
voltage to drop below 0.8 volts. Is it an intermittent switch? Does
purple wire voltage sometimes dip slightly below 5.00 volts? Or does
green wire drop for only one second after power switch if pressed?
Symptoms, when posted here, may also result in more useful
information.