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power on /reset switch problems



 
 
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  #1  
Old January 3rd 05, 10:44 AM
chris
external usenet poster
 
Posts: n/a
Default power on /reset switch problems

Hi,
my wife recently aquired an oldish ex work PC which I would like to reuse
for our kids as the spec is still resonable and it has a fiar amount of
memory /disk - however the problem is the power on and reset switches on the
main case. They only work perhaps once in 50 or so times so I wondered if
there was a way of replacing these or just bypassing the switches and
hardwiring and using the main PSU on/off switch to power the PC?

I'm not sure what effect taking out these switches would have.

Any ideas appreciated -

TIA
Chris


  #2  
Old January 3rd 05, 11:40 AM
David Maynard
external usenet poster
 
Posts: n/a
Default

chris wrote:

Hi,
my wife recently aquired an oldish ex work PC which I would like to reuse
for our kids as the spec is still resonable and it has a fiar amount of
memory /disk - however the problem is the power on and reset switches on the
main case. They only work perhaps once in 50 or so times


What are the symptoms, other than it not powering on. I mean, do the
switches 'stick' in one position or the other, or not move at all, or move
but no 'click', or what?

Look inside the case and see how they're mounted. Are they simply loose? Is
the mounting bracket broken off the front bezel support?

What I mean is, it may be possible to simply fix the ones that are there.

so I wondered if
there was a way of replacing these


Yes, they can be replaced but it's not easy to describe in text because
you're unlikely to find some place that sells a 'direct replacement' so
it's a matter of looking at them and finding something close enough to fit,
and that depends on being passingly familiar with typical switches and
perhaps some ingenuity in mating them to the existing brackets inside. If
it's a *simple* one it might simply be a round shaft, momentary, switch
screwed into a flat bracket behind the plastic pushbutton and another
'standard' round shaft, momentary, switch could be put in the same hole,
perhaps using the back nut to adjust how far/close to the plastic plunger
it is so it depresses and releases properly.

The generic solution is to buy a 'normal' pushbutton switch from some
generic supplier, Like radio Shack, and simply drill a couple of new,
correct size, holes in the front bezel, mount the new 'standard' switches
and move the power and reset wires to them. That means snipping the wires
off the old switches and soldering them to the new ones.

or just bypassing the switches and
hardwiring and using the main PSU on/off switch to power the PC?


Well, there's not really anything to 'bypass'. Wiring the power switch
permanently 'on' would cause the computer to turn itself right back off
after the 6 seconds, or so, "hold me down to power off' timeout and
'bypassing' the reset switch is "disconnect it," but since it don't work
anyway it's already 'disconnected'.

If the BIOS power settings can be set to always power on after a power
failure then you might be able to cycle the rear switch to turn it on but
that's really a kludge.


I'm not sure what effect taking out these switches would have.

Any ideas appreciated -

TIA
Chris



  #3  
Old January 3rd 05, 02:19 PM
chris
external usenet poster
 
Posts: n/a
Default

Thanks for the advice Dave -
I have since investigated further and after dismantling the case and got
access to the switches found that by pressing the power on switch directly
( i.e. not via the external case buttons) the power on LED flickers briefly
and then goes out - if I repeat the process the light doesn't even flicker
with the power remaining connected - (and the Pc doesn't acutally power up)
.. I have swapped the PSU and lead with a known working one and the same
happens - thus ruling out any PSU issues.
In summary the power on LED only lights after the power has been connected
for the first time and the PC doesn't power up - subsequent power on
attmepts don't even result in the LEd flicerking unless the power supply is
disconnected and reconnected.

At first I susepcted a blown fuse but the this appears not to be the case
as the process is repeatable.

Do you think this might be a switch problem or something more fundamental
? - unfortunately I don't know the background to this PC ( why it was being
discarded) but it seems worth saving i.e. PII processor full set of memory
and a reasonable hard drive)

Thanks
Chris


"David Maynard" wrote in message
...
chris wrote:

Hi,
my wife recently aquired an oldish ex work PC which I would like to reuse
for our kids as the spec is still resonable and it has a fiar amount of
memory /disk - however the problem is the power on and reset switches on
the main case. They only work perhaps once in 50 or so times


What are the symptoms, other than it not powering on. I mean, do the
switches 'stick' in one position or the other, or not move at all, or move
but no 'click', or what?

Look inside the case and see how they're mounted. Are they simply loose?
Is the mounting bracket broken off the front bezel support?

What I mean is, it may be possible to simply fix the ones that are there.

so I wondered if there was a way of replacing these


Yes, they can be replaced but it's not easy to describe in text because
you're unlikely to find some place that sells a 'direct replacement' so
it's a matter of looking at them and finding something close enough to
fit, and that depends on being passingly familiar with typical switches
and perhaps some ingenuity in mating them to the existing brackets inside.
If it's a *simple* one it might simply be a round shaft, momentary, switch
screwed into a flat bracket behind the plastic pushbutton and another
'standard' round shaft, momentary, switch could be put in the same hole,
perhaps using the back nut to adjust how far/close to the plastic plunger
it is so it depresses and releases properly.

The generic solution is to buy a 'normal' pushbutton switch from some
generic supplier, Like radio Shack, and simply drill a couple of new,
correct size, holes in the front bezel, mount the new 'standard' switches
and move the power and reset wires to them. That means snipping the wires
off the old switches and soldering them to the new ones.

or just bypassing the switches and hardwiring and using the main PSU
on/off switch to power the PC?


Well, there's not really anything to 'bypass'. Wiring the power switch
permanently 'on' would cause the computer to turn itself right back off
after the 6 seconds, or so, "hold me down to power off' timeout and
'bypassing' the reset switch is "disconnect it," but since it don't work
anyway it's already 'disconnected'.

If the BIOS power settings can be set to always power on after a power
failure then you might be able to cycle the rear switch to turn it on but
that's really a kludge.


I'm not sure what effect taking out these switches would have.

Any ideas appreciated -

TIA
Chris





  #4  
Old January 3rd 05, 06:27 PM
BBUNNY
external usenet poster
 
Posts: n/a
Default


"chris" wrote in message
...
Hi,
my wife recently aquired an oldish ex work PC which I would like to reuse
for our kids as the spec is still resonable and it has a fiar amount of
memory /disk - however the problem is the power on and reset switches on
the main case. They only work perhaps once in 50 or so times so I
wondered if there was a way of replacing these or just bypassing the
switches and hardwiring and using the main PSU on/off switch to power the
PC?

I'm not sure what effect taking out these switches would have.

Any ideas appreciated -

TIA
Chris


Start from the beginning. Use a screw driver touching the two posts to see
if
it will start and reset from there. This will tell if it is in the switch
or the Mainboard.
I have also seen this behavior with a bad BIOS flash. ie using a BIOS from
Asus instead of Hewlett Packard. But first find out if the switch itself is
broken.


  #5  
Old January 4th 05, 01:57 AM
David Maynard
external usenet poster
 
Posts: n/a
Default

chris wrote:

Thanks for the advice Dave -
I have since investigated further and after dismantling the case and got
access to the switches found that by pressing the power on switch directly
( i.e. not via the external case buttons) the power on LED flickers briefly
and then goes out - if I repeat the process the light doesn't even flicker
with the power remaining connected - (and the Pc doesn't acutally power up)
. I have swapped the PSU and lead with a known working one and the same
happens - thus ruling out any PSU issues.
In summary the power on LED only lights after the power has been connected
for the first time and the PC doesn't power up - subsequent power on
attmepts don't even result in the LEd flicerking unless the power supply is
disconnected and reconnected.


Has it EVER powered up? Because that sounds like a classic over-current
shutdown, meaning a defective component somewhere.

If something pulls too much current (like a defective CPU, defective
motherboard, defective hard drive, etc.) the PSU will go into an
over-current shutdown and it takes cycling the mains power off to reset the
over current protection circuitry.



At first I susepcted a blown fuse but the this appears not to be the case
as the process is repeatable.

Do you think this might be a switch problem or something more fundamental
? - unfortunately I don't know the background to this PC ( why it was being
discarded) but it seems worth saving i.e. PII processor full set of memory
and a reasonable hard drive)


Well, it may have been discarded because it wasn't working.

The thing that confuses me is you originally said 'once in 50 tries'.

What's the maker, model, motherboard, processor (as in WHICH P-II)?

And what was the 'known working' PSU? Just because it works in another
system doesn't mean it has enough power to run that one, whatever it is. I
mean, I can't say with no information on what they are.

If it's an over-current shutdown the question is what's causing it. I'd
strip it to bare bones and try to find what's causing the short. Unplug all
the IDE devices, hard drive, CD ROMs, etc. Unplug the floppy. Remove all
but one stick of RAM. Remove all PCI cards, leaving only the video adapter
and see if it'll power up. If not, pull the remaining memory and video
card. See if power will stay on. If not, remove the CPU and see if power
will stay on. It obviously won't *boot* without memory, video, and CPU but
we're just trying to see if the PSU will stay on, looking for the short.

If you get to where it'll stay on then put components back in, one by one,
till it again fails to power up and that one is likely to be the culprit.

Hopefully at least the motherboard alone will power up (if it's the
processor, P-II processors are very cheap these days. 11 bucks for a 450 at
www.starmicro.net)




Thanks
Chris


"David Maynard" wrote in message
...

chris wrote:


Hi,
my wife recently aquired an oldish ex work PC which I would like to reuse
for our kids as the spec is still resonable and it has a fiar amount of
memory /disk - however the problem is the power on and reset switches on
the main case. They only work perhaps once in 50 or so times


What are the symptoms, other than it not powering on. I mean, do the
switches 'stick' in one position or the other, or not move at all, or move
but no 'click', or what?

Look inside the case and see how they're mounted. Are they simply loose?
Is the mounting bracket broken off the front bezel support?

What I mean is, it may be possible to simply fix the ones that are there.


so I wondered if there was a way of replacing these


Yes, they can be replaced but it's not easy to describe in text because
you're unlikely to find some place that sells a 'direct replacement' so
it's a matter of looking at them and finding something close enough to
fit, and that depends on being passingly familiar with typical switches
and perhaps some ingenuity in mating them to the existing brackets inside.
If it's a *simple* one it might simply be a round shaft, momentary, switch
screwed into a flat bracket behind the plastic pushbutton and another
'standard' round shaft, momentary, switch could be put in the same hole,
perhaps using the back nut to adjust how far/close to the plastic plunger
it is so it depresses and releases properly.

The generic solution is to buy a 'normal' pushbutton switch from some
generic supplier, Like radio Shack, and simply drill a couple of new,
correct size, holes in the front bezel, mount the new 'standard' switches
and move the power and reset wires to them. That means snipping the wires
off the old switches and soldering them to the new ones.


or just bypassing the switches and hardwiring and using the main PSU
on/off switch to power the PC?


Well, there's not really anything to 'bypass'. Wiring the power switch
permanently 'on' would cause the computer to turn itself right back off
after the 6 seconds, or so, "hold me down to power off' timeout and
'bypassing' the reset switch is "disconnect it," but since it don't work
anyway it's already 'disconnected'.

If the BIOS power settings can be set to always power on after a power
failure then you might be able to cycle the rear switch to turn it on but
that's really a kludge.



I'm not sure what effect taking out these switches would have.

Any ideas appreciated -

TIA
Chris






  #6  
Old January 4th 05, 02:52 PM
w_tom
external usenet poster
 
Posts: n/a
Default

The power supply system is three components - PSU,
motherboard controller, and power switch. One gets the
essential (and so inexpensive) 3.5 digit multimeter to learn
from these procedures. Even if procedures don't tell you what
is wrong, the facts provided now means others can provide
assistance. Even swapping the power supply did not tell us
much useful information: "Computer doesnt start at all" in
alt.comp.hardware on 10 Jan 2004 at
http://tinyurl.com/2t69q and
"I think my power supply is dead" in alt.comp.hardware on 5
Feb 2004 at
http://www.tinyurl.com/2musa

Was the power supply dead? Without removing anything, that
meter could have reported same in seconds. Important voltages
for you will include Power OK and Power On. What do these do
as you try to power on system. Also if the essential 3.3, 5,
and 12 do not even attempt to power, then other voltages will
be shutdown. Again, how the voltages behave is important.

Lets not forget the lockout circuit found in that power
supply controller. Completely remove power cord from wall to
reset that lockout circuit. Again, you will be wasting time
and effort without the meter. So ubiquitous as to be even
sold in Home Depot, Sears, Lowes, and Radio Shack.

chris wrote:
Thanks for the advice Dave -
I have since investigated further and after dismantling the case
and got access to the switches found that by pressing the power on
switch directly ( i.e. not via the external case buttons) the power
on LED flickers briefly and then goes out - if I repeat the process
the light doesn't even flicker with the power remaining connected -
(and the Pc doesn't acutally power up) . I have swapped the PSU and
lead with a known working one and the same happens - thus ruling
out any PSU issues.
In summary the power on LED only lights after the power has been
connected for the first time and the PC doesn't power up -
subsequent power on attmepts don't even result in the LEd
flicerking unless the power supply is disconnected and reconnected.

At first I susepcted a blown fuse but the this appears not to be
the case as the process is repeatable.

Do you think this might be a switch problem or something more
fundamental ? - unfortunately I don't know the background to this
PC ( why it was being discarded) but it seems worth saving i.e.
PII processor full set of memory and a reasonable hard drive)

Thanks
Chris

 




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