Thanks kindly for all of the replies to my previous question. I've read
twice through each reply - some will take another run-through tomorrow to
really absorb, since I do want to understand it all completely

But, I just did an experiment which tells me that the PS is probably not
the problem. I borrowed a Compaq and pulled its working ATX PS. The
resulting behavior was the same - power on for a moment only.

Does this pretty much say that the PS is not the problem here? What
should be my next step in diagnosis?

From the reply by w_tom1, it seems I must check all the pins. Tom says to
check for shorts - but I have only a 9v analog powered multimeter, so I'd
think I can't use the ohm meter, except on 12v circuits, yes? Or do I use
the voltmeter and look for what pins stay mostly flat on voltage and
which pins might spike? Or does the analog meter (an old Radio Shack one)
respond too slowly to tell me anything?

Thanks again for all replies.

"Al" wrote in message
. ..
Thanks kindly for all of the replies to my previous question. I've read
twice through each reply - some will take another run-through tomorrow to
really absorb, since I do want to understand it all completely

But, I just did an experiment which tells me that the PS is probably not
the problem. I borrowed a Compaq and pulled its working ATX PS. The
resulting behavior was the same - power on for a moment only.

Does this pretty much say that the PS is not the problem here? What
should be my next step in diagnosis?

From the reply by w_tom1, it seems I must check all the pins. Tom says to
check for shorts - but I have only a 9v analog powered multimeter, so I'd
think I can't use the ohm meter, except on 12v circuits, yes? Or do I use
the voltmeter and look for what pins stay mostly flat on voltage and
which pins might spike? Or does the analog meter (an old Radio Shack one)
respond too slowly to tell me anything?

Thanks again for all replies.


The computer would start but then go only into standby mode (with the
power indicator being always yellow, never green). After a few days of
that behavior, it would then start only for a moment, and only with a few
spins of the ps fan (there is no CPU fan). Pushing the start button again
would have no effect - unless I removed the power cord and let it sit for
a minute or two. Then I'd replug and the pattern would repeat, with only
a momentary start for the first button press.


If the above is you problem it is similar to a Compaq I have and never could
fix. I have to power down the unit for at least 60 seconds, (with the AC
switch or unplugging it from the wall - NO AC at all!!!) then hold the start
button and restore AC.

It is something in the BIOS power saver firmware according to support
services. Changing it would have disabled the power down/sleep of the
computer so I put up with the button holding for years.

So - from cold (no AC) hold the start button on the computer then apply AC
power.

PP

First thing to do is reset the CMOS - a corrupted CMOS setting can result
in all sorts of strange behavior.

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"Al" wrote in message
. ..

But, I just did an experiment which tells me that the PS is probably not
the problem. I borrowed a Compaq and pulled its working ATX PS. The
resulting behavior was the same - power on for a moment only.

!!!

Are the wires on the connector of the Compaq PS all the same colors in the
corresponding locations?

Compaq made a lot of proprietary power supplies with the voltages all in a
non-standard order on the connector, but they used the standard type of
connector so you can plug it into any ATX board. At least they made them so
the wire colors indicate this, so you can tell if you are alert.

Dell later did the same thing, and still does. I am told by one guy that
Compaq follows the standard now.


--

Reply in group, but if emailing add
2 more zeros and remove the obvious.

On Sat, 22 Jan 2005 04:36:30 GMT, Al wrote:

Thanks kindly for all of the replies to my previous question. I've read
twice through each reply - some will take another run-through tomorrow to
really absorb, since I do want to understand it all completely

But, I just did an experiment which tells me that the PS is probably not
the problem. I borrowed a Compaq and pulled its working ATX PS. The
resulting behavior was the same - power on for a moment only.

Does this pretty much say that the PS is not the problem here? What
should be my next step in diagnosis?

Are you plugging ALL the wires back into everything?

A) I would just have PSU into MOBO and remove everything else (except
the front panel switches / LEDS) then test again (even remove addon
cards).

You don't need yer voltmeter yet as there's little to see.

Keeping it simple.

1) Test the PSU on the bench and see if it runs (loop test etc, fan
spins etc). If it won't run on the bench it won't run in the PC.

2) If 1) is ok then test it again in the PC with just the wires as A)
above

3) If 2) is ok (PC passes POST etc) Then switch off and add things
one-at-a-time (FDD and Power cable and power on, if ok then HDD and
power cable etc). If you get the machine back up and working you might
have an intermittent fault or a bad plug / cable / bad device.

The above has worked for me for the last 20 years (from when PSU's
were 63 W) ;-)

All the best ..

T i m

I don't believe I said anything about checking for shorts.
I said a certain behavior could indicate either a defective
supply, an overloaded supply, or a shorted voltage. We need
details of that behavior before we can move to the next step.

If you believe you have a short, then first you can say
which voltage is shorted. Again, that is what the meter would
have shown. The one voltage and did not rise is the suspect
voltage that would also cause other voltages to be shut off.
Again, which voltage? Given that information, then we can
continue to the next procedure.

The multimeter is not likely to be very good at detecting
shorts - depending on its design. Better meters will check
continuity with using less than 0.7 volts and less than 5
milliamps. No continuity meter better output the full nine
volts or even 3 volts. To the trivial current output by a
meter in conductivity mode, the entire computer is likely to
consume all that and more - therefore look just like a short.

Once we have information from previous readings, then we can
determine (without removing any power supply) if power supply
is overloaded, failing, or shorted.

Again, how to increase labor significantly. Remove the
power supply to test on a bench. Literally anything a bench
test is going to find - and more - is done with the supply
left in the computer.

Al wrote:
Thanks kindly for all of the replies to my previous question. I've
read twice through each reply - some will take another run-through
tomorrow to really absorb, since I do want to understand it all
completely

But, I just did an experiment which tells me that the PS is probably
not the problem. I borrowed a Compaq and pulled its working ATX PS.
The resulting behavior was the same - power on for a moment only.

Does this pretty much say that the PS is not the problem here? What
should be my next step in diagnosis?

From the reply by w_tom1, it seems I must check all the pins. Tom
says to check for shorts - but I have only a 9v analog powered
multimeter, so I'd think I can't use the ohm meter, except on 12v
circuits, yes? Or do I use the voltmeter and look for what pins
stay mostly flat on voltage and which pins might spike? Or does
the analog meter (an old Radio Shack one) respond too slowly to
tell me anything?

Thanks again for all replies.

In article ,
says...
Keeping it simple.

1) Test the PSU on the bench and see if it runs (loop test etc, fan
spins etc). If it won't run on the bench it won't run in the PC.



Tim, I'd read warnings that running the PSU with no load could ruin it.
Do you mean I should attach some load, or that I should turn the PSU on
for only a short duration? Or were the warnings overly cautious?

In article ,
lid says...
Are the wires on the connector of the Compaq PS all the same colors in the
corresponding locations?

yes, I'd heard about Dell's approach, so I asked on the Compaq group and
had gotten that tip. The Compaq had a white, which was lacking on the
Gateway - and the Compaq had one pin with 2 wires going to it - otherwise
they were the same

Also, some web vendors list the Compaq 152769-001 as ATX

"Al" wrote in message
. ..
In article ,
says...
Keeping it simple.

1) Test the PSU on the bench and see if it runs (loop test etc, fan
spins etc). If it won't run on the bench it won't run in the PC.



Tim, I'd read warnings that running the PSU with no load could ruin it.
Do you mean I should attach some load, or that I should turn the PSU on
for only a short duration? Or were the warnings overly cautious?

You should use a load, running it unloaded shouldn't damage anything, but
the voltages you see will likely be all wrong.

A power supply with no load OR with all outputs shorted
together causes no power supply failure, assuming the power
supply was properly designed. Furthermore, if someone says a
bench test with no load will ruin the supply, then that person
did not even learn power supply fundamentals.

You want to discover if a power supply is defective. That
means either tested in or outside the computer, you must still
obtain numbers. The multimeter is still required.
Furthermore, a power supply that appears OK on the bench can
still be defective. Power supply must be fully under load to
be tested.

No load is also why those power supply testers are myopic.
They cannot test when a power supply is most likely to
demonstrate its failure.

Furthermore, not all power supplies require a load to be
tested. This 'load' requirement is unique to each power
supply design. How much load is required is also a function
unique to each supply.

Keep it simple. Even on the bench, a test is insufficient
without a meter. With the meter, a better test is conducted
with supply still inside the computer - under load.

You saw the power supply do something particular. But you
did not report back what you saw. Appreciate that you are
starving me of details that could solve your problem quickly.
Appreciate that without removing anything, we can pretty much
isolate the problem down to one of three components in a power
supply 'system'. So which voltages rise on power up? Which
voltages do not? And what are numbers for other voltages
that, for example, must always be there?

The secret to solving simple power supply problems so quickly
- first get the facts - the numbers. Others make it vastly
more complex by shotgunning (putting a power supply on a
bench). Procedure to identify the failed component of that
power supply system takes only minutes. But it means working
smarter - not harder.

Reason to pull a power supply: after a few minutes of meter
readings, then it is obvious the power supply has failed.

Al wrote:
Tim, I'd read warnings that running the PSU with no load could ruin it.
Do you mean I should attach some load, or that I should turn the PSU on
for only a short duration? Or were the warnings overly cautious?

In article , says...
You saw the power supply do something particular. But you
did not report back what you saw. Appreciate that you are
starving me of details that could solve your problem quickly.

Sorry, Tom. I started a new thread asking about the bulging capacitors in
the computer. From all the replies about bad caps (and because a known
working ATX PSU showed the same behavior as the original PSU), I quickly
became convinced that the bad caps were the problem, not the PSU.

Thank you for the help.

Appreciate that without removing anything, we can pretty much
isolate the problem down to one of three components in a power
supply 'system'. So which voltages rise on power up? Which
voltages do not? And what are numbers for other voltages
that, for example, must always be there?


as I understand it, pin 9 should always have 5v - but when I measured
between 3 (ground) and 9 I got the same as I always get anyhwere on the
back of the ATX connector: a short tiny movement of the analog meter. I'd
guessed that an analog meter's needle can't react quickly enough to
adequately display a momentary voltage, so I don't know what the voltage
really was. (It showed maybe .5 volt.)

Same procedure to identify defective PSU also identifies
other defective components in that power supply 'system'.
Some caps will be part of the power supply controller located
on motherboard.

Again, if pin 9 is the purple wire (I don't remember), then
we have the culprit - or at least a usual suspect. If bulging
capacitors are connected to that power, then short probably
has been identified.

To properly identify that capacitor connects to pin 9, your
meter must be a newer design - so that its voltage does not
blow through and maybe even overstress IC P-N junctions. IOW
the meter's continuity tester must output no more than 0.7
volts and must limit current to single digit milliamps or
less. Some older meters output too much voltage and may
measure continuity through ICs where current is not expected
to flow. A low voltage continuity meter will only report
actual connections.

Using that meter, identify every electrolytic capacitor on
motherboard that connects to pin 9. Are they bulging? Those
capacitors can be replaced very cheaply - typically for about
$1 per cap. (BTW make note of which capacitor pin is ground
and which connects to +5 since electrolytic are polarized and
sometimes are installed backwards both during manufacturing &
repair.)

Above assumes no other peripheral is also shorting that 5VSB
(and I am assuming that pin 9 is the purple wire because the
question was not answered). IOW disconnect all peripherals
such as IO cards, keyboard, etc just to confirm they too are
not shorting that purple wire +5 volts always on voltage.

Don't remember if anyone mentioned it. But you must remove
power cord from wall before removing anything inside the
machine. If not, that five voltage should be powering
components as you remove them - bad for electronics not
designed to be hot popped.

Al wrote:
Sorry, Tom. I started a new thread asking about the bulging capacitors
in the computer. From all the replies about bad caps (and because a
known working ATX PSU showed the same behavior as the original PSU), I
quickly became convinced that the bad caps were the problem, not the
PSU.

Thank you for the help.

Appreciate that without removing anything, we can pretty much
isolate the problem down to one of three components in a power
supply 'system'. So which voltages rise on power up? Which
voltages do not? And what are numbers for other voltages
that, for example, must always be there?


as I understand it, pin 9 should always have 5v - but when I measured
between 3 (ground) and 9 I got the same as I always get anyhwere on the
back of the ATX connector: a short tiny movement of the analog meter.
I'd guessed that an analog meter's needle can't react quickly enough
to adequately display a momentary voltage, so I don't know what the
voltage really was. (It showed maybe .5 volt.)