Re: Really stumped: PS inoperative

On Apr 14, 2:09 pm, Haines Brown <bro...@xxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Yes, I suspected as much. Despite what I might have just reported in my
other message, with the PS power switch the green PS_ON wire reads
3.7V. When the front panel switch is depressed, the voltage drops to
zero. If I push the front button again, but hold it for a few seconds,
the voltage climbs back up to 2.5V. So it seems the latching mechanism
on the MB is not entirely dead.

The grey PWR_OK wire on the main power connector reads zero after the PS
switch is off for a while and when it is switched back on. If I now
press the front power button, it causes a little activity at this point,
but it quickly settles back to the 0.004V. This seems wrong. I gather
that the PWR_OK connection should be 5 V initially, and when the power
on button is depressed, drop down to 3.3V. I'm not getting anything like
that.

Important numbers are each wire voltage before and when the power
switch is pressed - as summarized in a previous post. For other's
benefit, what is happening here: isolated parts of that 'less than two
minute procedure' are eventually being performed.

What is called a 'latching circuit' is a power supply controller.
Power switch is only one controller input. Measuring that switch was
unnecessary if numbers from that two minute procedure were provided.
Again, numbers both just before and when power switch is pressed.

Irrelevant are voltages on green and gray wires without first
providing purple wire voltage (both before and when switch is
pressed). Purple wire provides power to the power supply controller
and can make that circuit work intermittently. Purple wire voltage
must measure above 4.87 VDC - and should be posted here because those
numbers may provide other information.

Before switch is pressed, green wire voltage must be well above 2.0
volts. When power switch is pressed, then green wire voltage drops to
below 0.8 volts. Last posts suggest that one part of the power
supply controller is working AND that the power switch is completely
OK. Two minute procedure made power switch testing unnecessary.

Moving on. Not provided were voltages on red, orange, and yellow
wires - each measured as the switch is pressed. Without what happens
on each wire and resulting numbers, useful information has been
withheld making the next paragraph an incomplete reply.

Gray wire must be something near zero before switch is pressed
(again, what was the actual number). When switch was pressed, what
happened to that gray wire voltage in the next 5 seconds? As I read
it, that voltage either starts to rise or never increases. Voltage
must be well above 2.4 volts within 2 minutes. That explains why
replacing a power supply would accomplish nothing. But without
specifically stating what gray wire voltage did and without voltages,
then too many possibilities still exist. No useful reply can be
posted without all those voltages in the two minute procedure.

I might bet one of the orange, red, or yellow wires will indicate
where to look next - what to suspect. But at least five other reasons
still exist which is why nothing more can be recommended until those
numbers are provided.

This paragraph is for others to learn from this discussion. A new
power supply solved nothing because the problem was not identified
first. A two minute procedure with a 3.5 digit multimeter that can
eliminate lost time and labor is "When your computer dies without
warning....." starting 6 Feb 2007 in the newsgroup alt.windows-xp
at:
http://tinyurl.com/yvf9vh

Among many things answered immediately in less than two minutes: is
the power switch good? Is the power supply defective? Are wires
properly connected? Nothing faster could have answered so much so
quickly.
.

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