wrote:
On Friday, February 12, 2016 at 8:21:47 PM UTC-8, David Farber wrote:
Jeff Liebermann wrote:
On Tue, 9 Feb 2016 10:17:14 +0000, Adrian Caspersz
wrote:

On 09/02/16 04:24, Jeff Liebermann wrote:
The hardware monitor is more commonly called the "power
good" line on an ATX power supply. It's suppose to be near +5V so
your +1.5v indicates that the power supply is not happy.
https://en.wikipedia.org/wiki/Power_good_signal

Agree with the caps diagnosis, I'd also follow the +5V standby
supply into the board with a meter while changing power state.

However, the +1.5V line, is that the CPU voltage voltage? 1.298V
looks in the ballpark for the CPU in that unit.

Try watching what the ATX power good gray wire does on a working
computah. There's small delay between turning on the power and when
the line goes high. Normal operation is a logic high which means
roughly +5VDC. +1.5V is definitely out of spec. I would venture a
guess that it's really oscillation or pulsing on the power good
line, which happens to average out to about +1.5V on a DVM.

Having the measured +1.5v be similar to the CPU voltage is
coincidence. Recycling the above Wikipedia page:
The ATX specification defines the Power-Good signal as a
+5 volt (V) signal generated in the power supply when it
has passed its internal self-tests and the outputs have
stabilized. This normally takes between 0.1 and 0.5 seconds
after the power supply is switched on. The signal is then
sent to the motherboard, where it is received by the
processor timer chip that controls the reset line to the
processor.

Cheaper and/or lower quality power supplies do not follow
the ATX specification of a separate monitoring circuit;
they instead wire the power good output to one of the 5 V
lines. This means the processor will never reset given
bad power unless the 5 V line drops low enough to turn
off the trigger, which could be too low for proper
operation.

I guess the easiest test is to just replace the PS with a known good
PS and see what happens. Checking the PS with a PS tester is also
useful. I have a really old and crude one but am considering
getting something like one of these:
https://www.google.com/search?q=atx+power+supply+tester+lcd&tbm=isch

Just to make sure we're talking about the same thing, I said:
"The only hardware issue I can find is that in the system bios,
there is a value in
the hardware monitor called, +1.5V and it hovers around 1.29V."
From what I understand, it's supposed to be 1.5V, not 5V.

I did swap the power supply with a working unit and the same thing
happened.

I used an ESR tester to test the caps on the motherboard and power
supply. They were fine.

Finally, I noticed that during an anti-virus update, the computer
froze up again. I uninstalled the anti-virus software (Avast) and it
hasn't locked up since. A few days later I installed AVG, and it's
still running fine. I also disabled the EIST service in the bios but
I'm not sure if that mattered at all.
http://www.intel.com/content/www/us/...000005723.html

What I never did figure out was why it took two power button pushes
to restart the computer after a freeze up. It reminds me of what
happens when you first apply AC to a computer (before even hitting
the power button) the power will briefly come on and then shut off.

Thanks for your replies.
--
David Farber
Los Osos, CA

ESR meters will not necessarily give a valid reading. SMPS need
really good caps so an ESR reading of 'good' may not, in fact, be
good enough. I was working on a PC power supply today only because it
is used in a very special computer and the manufacture is phasing it
out but our people intend to use them a few more years. One of the
caps I pulled read nothing on the meter but when I probed the board
where it was, the reading was 'good'.

Consider solid polymers if available. Otherwise I go for the highest
ripple current and longest hours rating. THEN price comes in to the
picture. My time is way more expensive than any capacitor I put in.

'Lytics on a motherboard over 5 years old are suspect and probably
need to go.

G²

Hi G^2

All very good points. I ran into this situation a few years ago and got some
very good advice here.
https://groups.google.com/forum/#!search/farberbear$20esr$20motherboard$20caps/sci.electronics.repair/-INdlCsyeJI/TqPCHmynoEUJ

Most notably the fact that many of the caps are in parallel and the ESR
readings should be much lower than out of circuit.

However, I see this present situation as perhaps two different problems
which a

Is the freezing problem really only software related?

Is the power up glitch ONLY after a freeze up a flaw or a feature?
Even when cold in the morning, it starts up fine if the night before it
powered down normally.

I'll go ahead and check out Jeff's suggestion:

"Will you please find a scope or voltmeter, attach it to Pin 8 (power
good) line of the ATX connector and see if there are any long delays,
oscillations, or complaints on this line that might inspire the
motherboard to shut down? Everything I read hear (except the
auntie-virus stuff) points to a power related problem. If the +1.5v
line is low, it might be defective RAM sucking excessive current from
the Vdd power line. Run a RAM test and see if you get it to fail."

Message to Jeff:
What exactly should I see on my scope at Pin 8 and am I monitoring this
constantly or only when I power up the machine? Also note that I did swap
all four RAM sticks with new ones and the same thing happened (before I
changed AV programs).

Thanks for your replies.
--
David Farber
Los Osos, CA