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When you're fairly certain that a motherboard trace is broken near the CPU (i.e.: you suspect heatsink / fan was improperly inserted) is it advisable to attempt a repair?

I've heard that it can be done using a substance for repairing embedded windshield defoggers. Has anyone had any experience with this?

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Don't use the stuff designed for windshield defoggers, that stuff is specifically designed to be resistive. You want to use something that is closer to the conductivity of the traces. I have successfully used that stuff to repair keyboards though. – Brad Gilbert Sep 14 '09 at 19:00
up vote 3 down vote accepted

Cut copper traces are not easily repairable using things around the house. Traces around the CPU are typically critical to the motherboards functionality.

First a few questions:

  • Is the cut trace visible? Typically copper traces around the processor are 4-5 mils wide (1 mil = 1 thousandth of an inch).
  • Is it just one trace that is cut? If a improperly installed heatsink has cut a trace, then more than just one trace could have been damaged.
  • Can you check with a meter to make sure that the trace is disconnected?
  • Does the cut trace connect to the memory slots or chipsets?

I've intentionally cut traces with a scalpel and it takes a little effort to do correctly. A heatsink cutting a trace is very unlucky.

To repair a trace (depending upon the size of the gap), I would use some solder and a small piece of bare wire, if necessary.

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I haven't inspected the board yet. I'm suspecting it's a broken trace due to the fact that it was running for a week, then the CPU fan broke. Customer's family member bought a new heatsink and fan, tried to install it, but it wouldn't "fit", when I was called in, the "legs" on the heatsink had to be realigned, and when all was attached, it would boot to Windows splash, then shut down.. then uptime got shorter and shorter... consistent with a heated broken trace... or traces, as you point out. – CoffeeBean Sep 12 '09 at 4:23
Without having the motherboard schematic and knowing exactly what traces were damaged, it is unlikely that you'll be able to reliably repair the motherboard. When/if you get the motherboard in hand and can inspect it, then you may be able to find the broken traces. If not too much damage is done, you can jump the trace with solder&wire by scraping off the solder mask from the trace. You will need a fine pitch soldering iron tip and some rework wire. If the trace is a high-speed signal, then it still may not be reliable and heat may affect the reconnected trace as well. – hanleyp Sep 12 '09 at 4:36
Must have been a scratched trace that got worse from overheating. – Brad Gilbert Sep 14 '09 at 19:02
I'd give all three credit for the answer if possible - so I'll just have to accept one and give everyone a "thumbs up" for the help. Would you believe it turned out to be the PSU??? – CoffeeBean Sep 15 '09 at 18:18

I have seen an experienced electrical engineer put a small wire-patch to the rescue on an old Macintosh Quadra 900 that was overclocked to 40MHz with a daystar accelerator that goes over the cpu. That block cooler + crystals slipped and cut a trace. This was repaired. It is therefore possible, but super tricky, and it gets much harder to do with current motherboards due to there being what... 900+ traces for the cpu? Also Mboards are multi-layered now, so it takes good fortune to have a fixable scratch.

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A Daystar "thing"? Are we talking about the Telephone/Internet provider, Daystar? – CoffeeBean Sep 12 '09 at 4:28
No CoffeeBean, we're talking old-school Their last gasp was a Daystar Mac Clone.… – dlamblin Sep 12 '09 at 6:12
Did I say last gasp? It was... but then they got bought, and sort of "revived" almost the way Polaroid is "revived" yet their building stands haunted by ghosts that can only travel in parallel lines. – dlamblin Sep 12 '09 at 6:18

well, there's a significant chance you won't get it to work, unless its the top layer - motherboard PCBs are multilayered and very carefully designed to keep traces precise lengths. I've heard of people fixing simpler pcbs with a conductive ink pen, but never a motherboard. I'd say, try it at your own risk, but replacing it would be what i recommend.

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I'm with you - but I'm trying to spare someone with poor judgment some expense. :) – CoffeeBean Sep 12 '09 at 3:33
Well, its a matter of, do you want to risk the CPU, ram or hard disk, to save the expense of a motherboard i suppose. – Journeyman Geek Sep 12 '09 at 5:54
All other hardware has been swapped out .. besides, RAM is cheap and the HDD has been imaged at the start. CPU is an unknown at this point and set aside for further testing. – CoffeeBean Sep 12 '09 at 10:31

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