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Old December 27th 08, 11:55 AM posted to alt.comp.hardware.pc-homebuilt
spodosaurus
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Posts: 410
Default PC power on - start, stop, start, stop, etc - eventually powersup

wrote:
On Dec 26, 7:03 am, spodosaurus wrote:
I have a problem that has only recently started (to my knowledge) and I
can't seem to solve it. ... once the system is warm (and sometimes
even from cold) a shutdown then start gets the compute spinning its
fans, powering off, spinning fans, powering off, and repeating this
cycle from 1-10+ times before actually POSTing. Once it POSTs, it's
all fine.


Fans spinning up and system not posting is a classic symtom of a
failed or
failing power supply. Also a failing power supply controller. Also a
video controller problem, etc. Most things replaced and swapped
would not address those symptoms and are classicshotgunning. In some
cases, if it fixed failure, it really only cured symptoms.

First establish what is and is not working. That means numbers and
simpler facts. Havinig swapped a power supply, nobody still knows if
either power supply is good or bad. Swapping determined nothing
useful. A perfectly good supply can be defective in another machine.
And a perfectly defective power supply can boot another computer.
Without numbers from a supply when powered off and as powering on,
then nobody knows if the power supply is good. With VDC numbers from
a 3.5 digit multimter, then a power supply's state is known AND in
seconds, also known is other power supply 'system' components such as
the supply controller and power switching.

By wildly speculating, a most likely reason for failure is a power
supply controller. Without numbers, every answer will only be
speculation.

Measure VDC on the green, gray, and purple wires (power supply to
motherboard) both before and when switch is pressed. Record those
numbers. Once the system does boot, measure VDC numbers from any one
of red, orange, and yellow wires. Only with numbers can we eliminate
power supply, its controller and other power supply system components
from the list of suspects. Only then do we have something on a list of
accomplishments. Only then move on to other potential problems. Only
then has labor provided numbers so that others can reply with useful
assistance.

Most items 'fixed' may have been eliminated immediately in the
minute a multimeter was learning numbers. Get the mulitmeter so that
a next reply is informative.


Hi,

Thanks for the reply.

My voltages were all within 5% of nominal voltages on both PSUs - I
tested these before I did anything else. I had a PSU test okay with my
digital multimeter before, but there were fluctuations on the +5VSB line
that were causing problems that were only detected by a PSU tester that
was inaccurate and only reported to one decimal place, but it did update
frequently enough that I could see the +5VSB fluctuations. Just in case
there was a +5VSB issue, I switch the rear usb power from that line to
+5V using the motherboard's jumpers without success.

Ari

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