Attn: Paul/WTomRe: Power up problem

On Jun 13, 10:09=A0am, brian (br...@xxxxxxxxx) wrote:
As of late, if I unplug my PC I can not power back up unless I jump across the
black/green pins on the 20 pin mb connector and them press my start button.

Under mormal shutdown conditions in which I power off it restarts fine..
it's only when I unplug it this happens.

W_Tom Replied
According to what was posted, the power supply is typically not the
problem. Problem is more likely in another section of the power
supply 'system' - the supply controller. Doing what Paul has
suggested will help trace that problem to its source. Another test
uses the multimeter to measure voltages on the orange, red, purple,
and yellow wires both before and when that switch is pressed (after
unplugging). Also useful is to measure voltages on green and gray
wires as power switch is pressed after an unplug. Report both the VDC
numbers and how those voltages responded as power switch is pressed.
Numbers in volts and seconds will make useful replies. Time, cost,
and labor to do what Paul has suggested and to obtain these numbers
will be less than 'swapping a supply only on a whim'.


from paul
The power supply is divided into two pieces. One tiny power supply, creates
+5VSB. +5VSB is used to power the motherboard logic, including the logic
handling the power switch. +5VSB must be present, in order for the power
supply to be started.

The second part of the power supply, has the 3.3, 5.0, 12V, -12V on it.
A voltage used to make the +5VSB, may also be used to operate the supervisor
for the other rails. If +5VSB is defective or shorted out, you might well
not see operation of the other half.

For reference, this is the only ATX power supply schematic that I've found
that is available for free.

http://www.pavouk.org/hw/en_atxps.html

This could also be related to the condition of the CMOS battery.
Use a multimeter, and check the CR2032 coin cell. A good value
is around 3 volts or so. Below 2.4V might cause a problem with
remembering the settings, or keeping the RTC clock running.
Replace the battery, and see if the symptoms change. It could
be, that your battery is completely flat, and that is preventing
the computer from starting normally.

Paul

Thanks to both of you for your replies. I have not been able to take any voltage measurements yet,
But to follow up"

Is it fair to say that the startup switch itself is not bad, if it were, it would not start
even when grounding the green wire on the 20 pin connection?

Also it seems to me I can rule out the CMOS battery or I would be losing date time and other info in my bios
if I lost power and the CMOS battery were dead.

I forgot to mention, this is an HP PC with a mb with no off/om rocker panel on th PSU. Also when this first
started happening simply unplugging the 20 pin connector and reconnecting it resloved the issue.

Luckily for me I don't lose power too often.

Thanks to both of you foe your replies.

Brian



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