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Windows 7: PC reboots if someone walk by

25 Feb 2010   #11
Dwarf

Windows 8.1 Pro RTM x64
 
 

Those mounting points are designed to be electrically connected to the chassis, hence the ring of solder to ensure a good contact with the mounting screws.

This does seem to be a strange problem, and it would seem to point to a grounding issue. Ensure that your motherboard is correctly mounted, following my advice about mounting points and screws. Check for electrical conductivity between the chassis and the earth terminal on the PSU socket. Plug the mains lead in (do not connect to the supply) and check that you have conductivity between the chassis and the earth connection in the plug. If not, check the mains lead for conductivity on the earth lead. Repair/replace if a fault is found. If you find no fault, then it might be a fault on your house wiring GET THIS CHECKED BY A PROFESSIONAL. If you have radiators in your room, then connect a wire between the chassis of your computer to the pipework of the radiators in order to provide a ground connection. Ensure that this connection is made to bare metal.


My System SpecsSystem Spec
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25 Feb 2010   #12
Darryl Licht

Windows 7 Ultimate 64 bit Steve Ballmer Signature Edition
 
 

Somethig to look at... some PSU's have a ground wire, some dont. Does yours? If so is it attached and properly grounded?

I have built hundreds of PC's over the last 17 years, usually problems like this are due to a loose nut behind the screwdriver! That is, it may be an electrical connector on the mobo not plugged in all the way, or improperly... a bent pin touching another, basically you may have missed or overlooked something.

Double and triple check every single connection, every pin, the front panel connections, usb, etc. Also look at the IO shield at the back of the PC, make sure one of the little metal "fingers" isnt grounding out a USB or Firewire connector.
My System SpecsSystem Spec
25 Feb 2010   #13
churin

W7 Ult x64 and W8 Pro x64
 
 

As a trouble shooting measure, I unplugged the reset cable and am waiting to see if the problem goes away. I have to wait for a day at least to determine if that will stop recurring the rebooting. I will post back.
My System SpecsSystem Spec
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25 Feb 2010   #14
Darryl Licht

Windows 7 Ultimate 64 bit Steve Ballmer Signature Edition
 
 

Please keep us informed of your progress...
My System SpecsSystem Spec
25 Feb 2010   #15
churin

W7 Ult x64 and W8 Pro x64
 
 

Quote   Quote: Originally Posted by Darryl Licht View Post
Please keep us informed of your progress...
I have determined that unplugging the reset cable from the header on the mobo prevents the rebooting.
Now I have plugged a reset cable on the header. The cable is not the one which is built in the case but a loose cable with a switch fitted on one end and a plug connector on the other end.
I will post back.
My System SpecsSystem Spec
25 Feb 2010   #16
Darryl Licht

Windows 7 Ultimate 64 bit Steve Ballmer Signature Edition
 
 

Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!
My System SpecsSystem Spec
25 Feb 2010   #17
churin

W7 Ult x64 and W8 Pro x64
 
 

Quote   Quote: Originally Posted by Darryl Licht View Post
Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!
Unfortunately not quite yet!
The resetting does not happen if the length of the cable for the reset switch is one inch but if it is 12 inches the problem(resetting) comes back. I am testing by inducing electrostatic charge in my body and discharging it by touching outer surface of the case.
I am beginning to think that I have to settle with having no reset switch or else ditch the case and pick a different one.
Attached are pictures of the machine:


Attached Thumbnails
PC reboots if someone walk by-img_4501x.jpg   PC reboots if someone walk by-img_4502x.jpg  
My System SpecsSystem Spec
26 Feb 2010   #18
Darryl Licht

Windows 7 Ultimate 64 bit Steve Ballmer Signature Edition
 
 

Quote   Quote: Originally Posted by churin View Post
Quote   Quote: Originally Posted by Darryl Licht View Post
Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!
Unfortunately not quite yet!
The resetting does not happen if the length of the cable for the reset switch is one inch but if it is 12 inches the problem(resetting) comes back. I am testing by inducing electrostatic charge in my body and discharging it by touching outer surface of the case.
I am beginning to think that I have to settle with having no reset switch or else ditch the case and pick a different one.
Attached are pictures of the machine:
What case? contact the manufacturer... tell them you have a bad rest switch or wire harness... they should send you a new one. How old is case?
My System SpecsSystem Spec
26 Feb 2010   #19
Dwarf

Windows 8.1 Pro RTM x64
 
 

A very strange one indeed. I am pleased that you have managed to narrow down the problem. What I think is happening, particularly when you say that a very short cable doesn't exhibit this phenomenom but a longer one does, is that the cable is acting like an aerial and picking up this charge somehow and causing the reset of your system. What I suggest is that you manually shield this cable by wrapping it in another wire which you connect to a good earthing point on your chassis. Try re-routing this cable away from the rest of the cables, particularly the PSU power harnesses.

Another test that you can do involves your PSU, or more specifically a certain connection. With reference to the following illustration, use a multimeter to back-probe the PWR_OK line on the main 20/24 pin ATX power connector. The connector pin numbers are 7 (black, COM) and 8 (gray, PWR_OK).

PC reboots if someone walk by-capture.png

With the meter connected, power up your system. Note that the voltage shown must lie within the range 2.4V to 6.0V, with a nominal value of 5.0V. Now, do what you have done before to reset your system by electro-static discharge. What happens to the voltage on the meter? If it falls below the 2.4V threshold (or, in rare occasions, rises above the 6.0V threshold) then you are suffering what is known as a brownout where the PSU fails to maintain the correct power output. This causes a timer chip on the motherboard to hold the reset line to the processor, thus preventing it from running under bad or unstable power conditions. When this voltage returns to its correct level, the reset line is released and the processor resumes operating, effectively beginning operation as if you had just powered the system on.

Again, referring to the illustration, there is another test. This involves the PS_ON# line. Connect your multimeter to the following pins on the connector: 15 (black, COM) and 16 (green, PS_ON#) or pins 13 (black, COM) and 14 (green, PS_ON#) depending on whether you have a 20-pin or a 24-pin connector. For normal running mode, this should show a reading of <2.0V. Again, reset your system by the electro-static discharge method. What happens to the reading here? If it becomes >2.0V, then the PSU voltages are disabled, effectively powering down the system.

Consequently, it may be prudent to check the main power switch as well as what you have already found out with the reset switch and, as I suggested, manually shield the cables and route them away from the rest of the cables, in particular the PSU power harnesses.


My System SpecsSystem Spec
26 Feb 2010   #20
churin

W7 Ult x64 and W8 Pro x64
 
 

Dwarf,
Thanks for your detailed suggestion.
I thought about shielding the reset cable and tried that but it did not solve the problem.
A lot of cables are run between the mobo and the front panel as shown below picture. I unplugged the audio, USB and eSATA cables from the mobo, and shielded reset, pwr and LED cables together by wrapping them by aluminum foil and grounded using a copper wire to one of the nine screws nearby. But no dice. I unplugged the reset cable from the mobo, then the resetting did not happen. Previous experiment indicated that the resetting does not occur even the rest of the cables from the front panel are connected to the mobo as long as the reset cable is unplugged.

Regarding your suggestion about checking voltage using circuit tester, is this for checking PSU if it is functioning normally or not?
I did functional test by putting all parts together on a table without using the case. It worked fine and I could install W7. At that time cable length of one inch each for the reset switch and pwr switch were used. I sometimes felt spark lightening happening when I touched the pwr or reset switch but it did not bother the system.

All those cables(reset, pwr, usb, eSata, LED, audio) are tightly bundled together which was done by vendor of the case. The main power supply cable is running reasonably away from the rest of the cable harness.


Attached Images
PC reboots if someone walk by-img_4500x.jpg 
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