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-   -   How to find a short on the motherboard (http://www.syschat.com/how-to-find-a-short-motherboard-3191.html)

powerjackrepair 02-19-2008 01:42 PM

How to find a short on the motherboard
 
Hi there, we are trying to find a short on one of our client's motherboards, we do not know which component causes a short, we do use a multimeter but it always shows zero since there is a short all over basically when we connect a multimiter to the postivie and the negative end it always gives us zero ohms resistance since it is shorting, but where, that we can't figure out. Any help would be appreciated on what equipment to buy,
we heard something about 4 wire digital multi meters any one knows if they work, and where to get them?
Thank you
Alex

squirrelnmoose 02-19-2008 06:03 PM

Start by doing a good close up visual inspection.
A short like that is usually in the power supply section of the board and is most of the time visible. Look for a blown transistor or capacitor on the board most likely in the power section.

Here are 3 examples of what to look for.
fisher-Paykel motor controller - Electronic Circuits Projects Diagrams Free

Bottom pf page on this one, right click view image to see full size.
Oh no! Edo Blog, Again! - BLOG Archives: Computer and IT

lx50

If you find something, pull it off, check if the short is still in the board.
Also consider how much time you are willing to invest versus the cost of replacement.

by the way, Desktop or Laptop?

lurkswithin 02-19-2008 07:33 PM

A direct short is usually shown as a burned spot around the part that shorted and will most likely smell really bad. Remove the board and examine it from both sides for the burned spot...if you still can't find it sniff the board and it will give you a general location as to what may have been shorted....as sometimes a chip may short under itself and will not show...but the smell all ways gives it up. Look for an expanded top on the can filters also...they should be flat on the top and not rounded.

You can't check chips and transistors while they are on the board...so again as with S-n-M asked how far are you going to go and at what cost of labor hours. To hunt down a short and spend the time to repair it and all that usually costs two or three times what it would to buy a new board....on top of that, my experience has shown that repaired boards just do not last that long to begin with so you might end up with a mad customer if he pays for repairs and something else shorts out in a week or two!

powerjackrepair 02-19-2008 09:16 PM

Thank you guys
 
Guys, thank you so much for participating. The board is from a laptop computer, it is not our first board to have a short issue on the motherboard, we had about 10-15 last year alone and there isn't much we can do about these, our methods are basically trying to remove a few components from the board near the dc power jack and if the short goes away put things back together hoping that it will fire up, the success rate is about 30% but the amount of time it takes removing components (carefully) from the board near where the dc jack is at is extremely time consuming. There has to be a better, easier way to find shorts on MB (and no visually we can't see which one is burnt). It is not only this board that we need the tools to find the shorting, we would really like to know what tool to use to trace where the short is at, and if there are any for sale we would love to buy them.
Thank you
Alex

squirrelnmoose 02-19-2008 09:38 PM

I don't have much more than a resource for board level repairs. This is where I started. They have equiptment to replace most types of IC's and good board level techs. Also a good resource for parts if you could use that.
SDA - System Design Advantage, LLC


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