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I found it!


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#1 Tracer3

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Posted 13 February 2010 - 12:11 PM

Some time back I asked if anyone had knowledge of problems concerning dissimilar metals being in contact with each other in the internal components of a PC that would cause problems IE (electrophoresis). I got some good advice about static discharge - which I took. The problem of electron transfer still bothered me. Yesterday I was cannibalizing a 2006 computer for parts and found evidence of electrophoresis on the motherboard where the screws attach the motherboard to the mounting platform. I had problems with this computer that I could never diagnose. I had finally given up and started using it for parts. I was sure it was a HDD issue but when I pulled it out and tested it it was fine - no viruses, spyware, bad sectors - nothing. The optical drives were the same, no problems. At this point I was POed that I had scrapped a good computer to fix a lesser one. I was pulling cables out when I saw the screws that held the motherboard showed oxidation. There is only one thing I know of that can cause this condition - electrophoresis. On steel this is called rust and is red and easy to see. Oxidation caused by dissimilar metal contact is most often white and can build up under screw heads where it cannot be seen until the damage has been done and it spreads to the outer surfaces. I am not a physicist, so problems arising from differences in electronegativity are beyond my knowledge. To make up for this I have devoloped a high level of suspicion and paranoia. Kind of works - somtimes. Planned obsolescence explains a lot of things and this may be one. I think its a plot to keep us buying more stuff. If it isn't a plot why have I never seen this discussed? It is a real issue, so that leads me to the conclusion that it IS a plot and you are all in on it. Ah HA, I knew it! What do you think?

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#2 Baltboy

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Posted 13 February 2010 - 12:34 PM

Most newer boards are built with solder "standoffs" to keep the screw from actually contacting any thing on the board itself. Older boards required an paper or cardboard washer to be placed between the board and screw to prevent accidental contact. There are really low levels of electricity running throught the motherboard and the connects are routed around the screw locations so the possiblility of electrical transfer is non-existant without direct contact. Most of the motherboard standoffs shipped with the boards now are dielectric metals which would eliminate the prospect of electrophoresis. One of the reasons I always recommend if you haven't rebiult your PC in a while to replace the standoffs as some of the older standoffs were just straight brass.

Edited by Baltboy, 13 February 2010 - 12:35 PM.

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#3 Tracer3

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Posted 13 February 2010 - 04:08 PM

I'm on a new build right now and it has the solder stand offs. It has brass stand offs mounting the board with zinc coated screws holding the board screwed into the brass. The brass stand offs are screwed into a steel mounting platform. The board is grounded from the power supply through a mounting hole in the board which has no solder stand offs. So the ground is copper, the screw is zinc plated pot metal screwed through the board into a brass stand off which is in turn screwed into the steel mounting plate. Problem or no? By the way, Thank you. (the stand offs LOOK like brass)

Edited by Tracer3, 13 February 2010 - 04:11 PM.


#4 garmanma

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Posted 14 February 2010 - 01:42 PM

The solder trace surrounding the mounting hole is actually part of the ground plane
The main reason for the insulated washers was/is motherboard/case mismatch.
Especially when the standoffs were punched into the mounting plate and not threaded stand-offs
If they do a crappy wave solder job on the motherboard, you might have parts grounding out
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