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How do I prove poor AC input?

Posted on 2006-11-21
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Last Modified: 2010-04-26
Hi, I see this power problem from time to time but would like an explanation for my customer:
The PC will not start up or will cycle itself off and on intermittently or even reboot unexpectedly.
But when it is moved directly to a different wall outlet on a different AC circuit and/or removed from
the surge bar and plugged directly into the wall, the problems go away.

This can happen even after replacing the power supply with a "high-end" good one. So, what is it about
the AC input side of the power that can cause the problem? How do I test and PROVE it's a problem
with the customers' wiring or utility?
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Question by:Oyster55
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by:My name is Mud
ID: 17988453
A fan or a light bulb might help, you might see the changes in voltage...
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by:mluther223
ID: 17988489
Wow,  can't help you with an explaination, but I wish I could reward you with a few points for answering a current problem I am experiencing.  I just moved into a old house, and occasionally my computer will reboot and/ or cycle itself on off.  I was thinking it might be a problem with my video card overheating.  I've been running a monitoring program to record the temperatures of CPU/ Video Card/ Hard drive...etc for a week,  but of course since installing the software I haven't had the computer malfunction....  I'm thinking this  is probably the culprit...the house is old (circa 1910) and only has 150 service.... Thanks
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by:Callandor
ID: 17988601
Just measure the wall outlet with a multimeter - if the voltage isn't within 10% of the rated voltage, equipment behaves very badly.  The same thing happens when brownouts occur, and the solution is to get a UPS to smooth out fluctuations and dips.  If it's local to an outlet, there may be a load on the circuit that causes the fluctuation, typically an appliance that draws a lot of current.
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Expert Comment

by:SRWright
ID: 17988621

If you have access to a Smart UPS device, they will be able to monitor the condition of the inbound power.  The APC Smart devices will show you if you have dirty power, spikes, drops... you name it.

In the situation that you are describing, I would advise an UPS anyway.
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Expert Comment

by:DanCh99
ID: 17988695
would something like this meet your needs?
https://isswww.co.uk/productdetail.aspx?id=3470

or contact a local electrician, and ask how they'd do it.
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Expert Comment

by:pgm554
ID: 17988840
Why waste your time?

It's just more efficent to use a UPS.

Basic UPS is under $100 bucks and requires no tech skills.

There are many reasons for weird power:

Neutal and ground reversed,electric motor or compressor on the same circuit,bad wiring,flakey breaker and the list goes on.
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by:Zephirus79
ID: 17989604


EASY!


Just go buy a voltmeter.   Put it in the wall at the customers place.  Should be 110-120 volts.   Now plug in the power cable and put the voltmeter on the other end of the power cable.   you should have the same 110-120 volt reading.  

If you have it there, then sorry to say, it IS either the power supply or the motherboard itself.   If if goes that far, check power settings in the BIOS.  A lot of times you can regulate voltage there too.  

This is assuming you are in the USA and you have the switch on the power supply set for the right voltage.  
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pgm554 earned 500 total points
ID: 17989812
Doen't work like that.

There are things likes spikes,ground noise,and undervoltages that last for millisecounds that can cause all kinds of issues.

So going in with a DVM is like a doctor using a stethescope,a usefull tool,but limited in what it tells you.

If you want a hard copy, no non-sense tool ,you use something like a Dranetz

http://www.dranetz-bmi.com//products/prodspec.cfm?prod=3

You can rent one,but as I said ,just cheaper to install a UPS.
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Author Comment

by:Oyster55
ID: 17990556
Yes, this last time it happened, I installed a UPS, and the problem disappeared at the customer's
site. It was NOT a power supply problem. Better UPSs have monitoring software which record
and track the voltage levels over a period of time. I can use this to show the customer what's
happening.
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