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  #1 (permalink)  
Old 12-08-2011, 06:23 PM
Rboats
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Default HP Pavillion a712n desktop problem


How to remove on/off button and troubleshoot or replace. Currently it
sticks when pushed in, it would sometimes pop back to regular "on"
postion and power up and process..now it will power up but won't
processs, sometimes get the error screen that that starts the countdown
to start in normal mode but after countdown to zero..nothing happens,,
I'm not a comp wiz but a all around DIY'er with everything else so now
it's computer time. Just don't want to destroy any components while
trouble shooting. Think I just need to replace On/OFF button. Any help
greatly appreciated. Thanks,Randy



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  #2 (permalink)  
Old 12-08-2011, 08:40 PM
rb
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Default Re: HP Pavillion a712n desktop problem


For an ATX power supply you need a 'momentary contact switch' such as
this one-->
http://www.radioshack.com/product/in...entPage=search



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  #3 (permalink)  
Old 12-08-2011, 10:36 PM
Paul
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Default Re: HP Pavillion a712n desktop problem

Rboats wrote:
> How to remove on/off button and troubleshoot or replace. Currently it
> sticks when pushed in, it would sometimes pop back to regular "on"
> postion and power up and process..now it will power up but won't
> processs, sometimes get the error screen that that starts the countdown
> to start in normal mode but after countdown to zero..nothing happens,,
> I'm not a comp wiz but a all around DIY'er with everything else so now
> it's computer time. Just don't want to destroy any components while
> trouble shooting. Think I just need to replace On/OFF button. Any help
> greatly appreciated. Thanks,Randy


The front panel of your computer, will have four or five twisted pair
wire things, coming from the panel to the motherboard "PANEL" header.

On my computer, the wiring looks like this. Separate wire pairs,
and much easier to deal with when maintenance is required.

http://imgs.inkfrog.com/pix/sceusa/CASE_FRONT_wires.jpg

What you'd notice, if that was the case, is that the "RESET" and
"POWER" switch connectors, are the same shape, and are 1x2 connectors.
Both the RESET and POWER switches are "momentary contact" type.

And that means, you can unplug the "POWER" one, unplug the "RESET" one,
and push the "RESET" one into place, where the "POWER" one used to be.
Then, when using the front panel controls on the computer, the tiny
RESET button performs the power on/off function. You can forget about
the reset function, as it is optional for the moment. That's the
quickest way to get the computer running again, if the POWER
button itself is busted.

As the other respondent "rb" says, a momentary contact switch type
is what you want. The fun part, is getting it connected (if you want
to replace the button itself).

*******

On things like pre-built computers, instead of individual wire
pairs, you may notice a "monolithic block", like a 2x4 or a 2x5
or the like, which slides as one unit, onto the motherboard
PANEL connector. That's a little less convenient to deal with.
They do them that way, to speed up the manual assembly procedure
when constructing the computer at the factory.

To change the wiring in the polyester black shell, you can
lift a tab on the side of the block, to release the pin and
allow it to slide out. This only works, if the polyester shell
uses tabs of that type. In this case, you'd move the RESET pair
of wires, into the position the POWER pair used to take. Total
of four tab manipulations, two to release the POWER wires,
two to release the RESET wires, and then push the RESET wires
into the POWER holes. Front panel switches are not polarized,
so on a wire pair, it doesn't matter which lead goes in which
hole of the pair. (LEDs on that connector, *are* polarized, and
you have to be more careful if rewiring LED indicators in the
block.)

http://www.frontx.com/head_con.html

The "lifting of tabs" thing is only required, if the PANEL wiring
assembly is one monolithic block and the wire pairs are
not separable. If your computer actually has individual 1x2
connectors, the switching of the wiring will go much faster.

*******

You can find sellers on Ebay (likely in China), who will sell
a wire assembly and switch, ready to use.

http://www.ebay.com/itm/PC-Case-Fron...item3a6a4d2b34

That would work, if you had the individual wire pairs kind of
computer, as you could then install a new switch, and plug the
1x2 connector onto the appropriate pair of pins on the PANEL
header.

Radioshack isn't likely to carry an exact assembly like that,
but a local computer store may have them. I have several
computer recyclers in town, and that would be another place
to look for a reasonably priced solution. You could even bring
in the switch in your current case, for a visual match of
dimensions (better chance it will fit).

I leave the buttons hanging down from my current case. They're
not in the holes in the front panel. That makes it easier for me
to remove the front panel to replace optical drives and the like.
My LEDs are actually mounted in the metal frame of the computer,
so when the panel comes off, there are only "light pipes" in the
plastic, to couple the light from the LED, into the front panel
indicators. That way, my panel has no wires at all on it any more.
But I do have an unsightly power and reset switch, hanging down
from the sides of the computer :-) For that quality, ghetto look :-)

It could be, that by easing the switch out of the panel,
and leaving it hanging down, the switch won't bind and will
work smoother. You never know...

Paul

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  #4 (permalink)  
Old 12-08-2011, 11:36 PM
philo
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Posts: n/a
Default Re: HP Pavillion a712n desktop problem

On 12/08/2011 05:36 PM, Paul wrote:
> Rboats wrote:
>> How to remove on/off button and troubleshoot or replace. Currently it
>> sticks when pushed in, it would sometimes pop back to regular "on"
>> postion and power up and process..now it will power up but won't
>> processs, sometimes get the error screen that that starts the countdown
>> to start in normal mode but after countdown to zero..nothing happens,,
>> I'm not a comp wiz but a all around DIY'er with everything else so now
>> it's computer time. Just don't want to destroy any components while
>> trouble shooting. Think I just need to replace On/OFF button. Any help
>> greatly appreciated. Thanks,Randy

>
> The front panel of your computer, will have four or five twisted pair
> wire things, coming from the panel to the motherboard "PANEL" header.
>
> On my computer, the wiring looks like this. Separate wire pairs,
> and much easier to deal with when maintenance is required.
>
> http://imgs.inkfrog.com/pix/sceusa/CASE_FRONT_wires.jpg
>
> What you'd notice, if that was the case, is that the "RESET" and
> "POWER" switch connectors, are the same shape, and are 1x2 connectors.
> Both the RESET and POWER switches are "momentary contact" type.
>
> And that means, you can unplug the "POWER" one, unplug the "RESET" one,
> and push the "RESET" one into place, where the "POWER" one used to be.
> Then, when using the front panel controls on the computer, the tiny
> RESET button performs the power on/off function. You can forget about
> the reset function, as it is optional for the moment. That's the
> quickest way to get the computer running again, if the POWER
> button itself is busted.
>
> As the other respondent "rb" says, a momentary contact switch type
> is what you want. The fun part, is getting it connected (if you want
> to replace the button itself).
>
> *******
>
> On things like pre-built computers, instead of individual wire
> pairs, you may notice a "monolithic block", like a 2x4 or a 2x5
> or the like, which slides as one unit, onto the motherboard
> PANEL connector. That's a little less convenient to deal with.
> They do them that way, to speed up the manual assembly procedure
> when constructing the computer at the factory.
>
> To change the wiring in the polyester black shell, you can
> lift a tab on the side of the block, to release the pin and
> allow it to slide out. This only works, if the polyester shell
> uses tabs of that type. In this case, you'd move the RESET pair
> of wires, into the position the POWER pair used to take. Total
> of four tab manipulations, two to release the POWER wires,
> two to release the RESET wires, and then push the RESET wires
> into the POWER holes. Front panel switches are not polarized,
> so on a wire pair, it doesn't matter which lead goes in which
> hole of the pair. (LEDs on that connector, *are* polarized, and
> you have to be more careful if rewiring LED indicators in the
> block.)
>
> http://www.frontx.com/head_con.html
>
> The "lifting of tabs" thing is only required, if the PANEL wiring
> assembly is one monolithic block and the wire pairs are
> not separable. If your computer actually has individual 1x2
> connectors, the switching of the wiring will go much faster.
>
> *******
>
> You can find sellers on Ebay (likely in China), who will sell
> a wire assembly and switch, ready to use.
>
> http://www.ebay.com/itm/PC-Case-Fron...item3a6a4d2b34
>
>
> That would work, if you had the individual wire pairs kind of
> computer, as you could then install a new switch, and plug the
> 1x2 connector onto the appropriate pair of pins on the PANEL
> header.
>
> Radioshack isn't likely to carry an exact assembly like that,
> but a local computer store may have them. I have several
> computer recyclers in town, and that would be another place
> to look for a reasonably priced solution. You could even bring
> in the switch in your current case, for a visual match of
> dimensions (better chance it will fit).
>
> I leave the buttons hanging down from my current case. They're
> not in the holes in the front panel. That makes it easier for me
> to remove the front panel to replace optical drives and the like.
> My LEDs are actually mounted in the metal frame of the computer,
> so when the panel comes off, there are only "light pipes" in the
> plastic, to couple the light from the LED, into the front panel
> indicators. That way, my panel has no wires at all on it any more.
> But I do have an unsightly power and reset switch, hanging down
> from the sides of the computer :-) For that quality, ghetto look :-)
>
> It could be, that by easing the switch out of the panel,
> and leaving it hanging down, the switch won't bind and will
> work smoother. You never know...
>
> Paul



Good answer

the reset button is not a good idea anyway

if the machine is having problems,
if the power button is depressed the system should go into a safe shut
down...

and if it's totally locked up
just killing the ac should do the trick

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  #5 (permalink)  
Old 12-09-2011, 02:22 PM
rb
Guest
 
Posts: n/a
Default Re: HP Pavillion a712n desktop problem


In a nutshell...the ATX power switch works by momentarily shorting the
connection between two pins on motherboard which sends a signal to turn
on the PC. A sticky or broken switch can cause a 'no start' or a 'reboot
loop' condition.

To remove switch:
Shut down PC, disconnect power cord.

Open PC case.

Remove front bezel covering (a tab or screw is usually located on every
corner of bezel).

Locate the power header(usually a double row of ~12 pins) on
motherboard. Two wires, usually green and white designate the power
switch leads. Disconnect them from motherboard.

Remove power switch from front bezel by removing the screws(if any) then
press power switch out of bezel. If it has no screws, it should snap
out.

A sticky switch could be caused by a bit of grit or grime stuck inside.
You can try cleaning the switch with a small amount of rubbing alcohol.
-Make sure the switch is completely dry before reconnecting to
motherboard header!-.
If cleaning does not work, replace the switch using a 'momentary contact
switch' such as this-->
http://www.radioshack.com/product/in...entPage=search



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  #6 (permalink)  
Old 12-11-2011, 10:26 AM
Paul
Guest
 
Posts: n/a
Default Re: HP Pavillion a712n desktop problem

Rboats wrote:
> Rboats;1320047 Wrote:
>> How to remove on/off button and troubleshoot or replace. Currently it
>> sticks when pushed in, it would sometimes pop back to regular "on"
>> postion and power up and process..now it will power up but won't
>> processs, sometimes get the error screen that that starts the countdown
>> to start in normal mode but after countdown to zero..nothing happens,,
>> I'm not a comp wiz but a all around DIY'er with everything else so now
>> it's computer time. Just don't want to destroy any components while
>> trouble shooting. Think I just need to replace On/OFF button. Any help
>> greatly appreciated. Thanks,Randy

>
> I pulled off the "broken" pushbutton and just left it with the little
> "tit" to try to start comp. Now I push the on button "tit" and it tries
> to start and just turns right off after 3-4 seconds. It just cycles like
> that. on 2-3 seconds then off 2-3 seconds then off. It just cycles like
> that til I kill the power source.
> so whats the problem anyone..I'm a novice here so please be kind......
>
>


It could be related to the switch remaining in the closed position.
The switch contacts are supposed to be released, after a short
push to start the computer. If the switch is smashed and permanently
shorted, that wouldn't happen.

But the thing is, before you pressed it, it wasn't making contact.
The computer did not try to start. Now, when you press the button,
the computer misbehaves. To me, that suggests a power supply problem.

So if I was fixing it, I'd pursue both possibilities.

1) Examine the power switch, as it comes from the front panel. Two
wires go back to the PANEL header. Using a multimeter set to the
ohms scale, probe the 1x2 interface of the switch, and see if
there is a permanent short (zero ohms) between the two pins. That
would tell you the switch is defective. The switch on a computer,
by definition, is "momentary ON", meaning normally it is an open
circuit or infinite ohms. Pushing the button, shorts the two signals
together for a fraction of a second. Releasing the button again, it
goes to infinite ohms.

If the switch state seems to be properly reflected on the multimeter
display, then you know it is not a switch problem.

2) The power supply could have become "weak". Maybe the +5VSB is no long
able to stay running, when the computer tries to operate. Maybe the main
part of the supply is weak. Or, it could be the PS_ON# signal is sitting
between logic zero and logic one, and that has been known to make the
main portion of the supply to behave weakly.

It can be difficult to assign blame in this case. Normally, you'd start
by assuming a faulty power supply (because percentage wise, they have
a higher failure rate than motherboards). The thing is, you can't tell
by looking at it, whether the motherboard is putting out a crappy PS_ON#
signal on the main power supply cable, or the power supply isn't listening
to the signal properly.

Swapping parts, is one way to test. Rather than waste the time on other
test strategies, I'd just swap in a spare ATX PSU and see if that helps.

If you're a "scientist type", then you'd study the PS_ON# signal. That
would require the purchase of an ATX power supply cable extender (20 pin
to 20 pin, foot long cable). You'd cut the PS_ON# wire in two, and that
gives access to current flow readings and voltage readings. I might use
two multimeters in that case, one in series to measure current, and
one set up to measure voltage with respect to ground. Then, I'd monitor
what happens when the motherboard doesn't want the supply on (logic 1,
greater than 2.0V level and hopefully, pretty close to 5.0V level), versus
when the motherboard wants the supply on (logic 0, less than 0.4V level,
and closer to zero volts the better the circuit is working). When making
logic 0 and logic 1 signals, the circuit will sink or source current,
which you would measure with the multimeter that is set to measure current.

If you wanted to evaluate the "drive capability" of the PS_ON# motherboard
hardware pad driver, you could add a resistive load to the circuit (place
load on the PS_ON# signal, on that piece of extension cable).

Those are the kinds of things you might do, to determine which end of the
link is at fault. Is the motherboard not able to drive a good signal ?
Or, is a good signal being driven, but the power supply has a defect that
makes it "blind".

As you can see, in the time it has just taken me to write that description,
I could have installed a spare power supply :-)

In any case, those are my two suggestions. If you have a multimeter,
check that the switch state is reflected properly on a multimeter
set to the ohms scale.

If you don't own a multimeter, just swap in another ATX power supply.

Doing the "scientist thing", would take half the day, but eventually,
you might be able to tell the difference between bad motherboard
and bad supply. And instead of spending $50 on a new supply, you'd have
spent $10 on a disposable cable, plus whatever precise item needs to be
replaced as a result of your "scientific testing".

*******

If you need help selecting power supplies, the process starts with looking
at the label on the old one. Every number on the thing means something.

If you can find a picture of the label, or post a picture on a site
like imageshack.us or similar, then perhaps someone here can suggest
the nearest equivalent.

For example, in this picture, I can see I'm dealing with a
Sparkle brand PSU, with model number ATX-400PN. DC Output is 400W.
Each rail is specified. If I had the numbers, I could find another,
similar supply for sale.

http://images17.newegg.com/is/image/newegg/17-103-013-S03?$S640W$

You can substitute a higher capacity supply, for a lower capacity one.
The capacity, is the maximum power it can provide. If your computer
only draws 100 watts, then 100 watts comes from the power supply,
not 400 watts. If your computer needed to draw more power, and
kept drawing more power, the power supply would shut off at
just a bit more than 400 watts (as it starts to overheat inside).

So if you bought a 500W one, and the motherboard draws 100 watts,
then there is still just a 100 watt flow from the wall, not 500 watts.

The only problem with higher capacity supplies, is their physical size.
A 1500 watt power supply, would have a very long casing on it, and
would not fit a tiny computer case. And as well, it would cost $$$,
so you wouldn't really want to buy one that large. That's for
rich guys, with four video cards inside the computer.

Paul

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