replace caps on motherboard issue
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Posted by robm on November 7, 2005, 7:00 pm
Please log in for more thread options i have a dead mobo that has domed caps, not worth sending off but worth an attempt at repair i am amateur solderer i have couple different weller irons 15w 25w 60w I read somewhere about cutting the caps in half and exposing the two cap posts then soldering new caps to the posts instead of trying to completely remove and replace the caps Is this a bad idea ? is there a good reason not to repair this way ? TIA robm | |||||||||||||||||||
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Posted by w_tom on November 7, 2005, 2:58 pm
Please log in for more thread options With a solder sucker, you need not do that. The spring loaded solder sucker will pull solder out of the hole so that a new cap can be properly mounted. It is far better - more reliable - to install new caps properly. robm wrote: | |||||||||||||||||||
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Posted by John Popelish on November 7, 2005, 6:32 pm
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robm wrote: > i have a dead mobo that has domed caps, not worth sending off but worth an
> attempt at repair > i am amateur solderer i have couple different weller irons 15w 25w 60w > > I read somewhere about cutting the caps in half and exposing the two cap > posts then soldering new caps to the posts instead of trying to completely > remove and replace the caps > > Is this a bad idea ? > is there a good reason not to repair this way ? > I haven't done it as you describe, but I can understand why someone may have come up with that method after destroying an otherwise good board trying to get the wires out with just an iron. The problem is that these boards are at least 4 layers, with the caps soldered to vias that connect to big pours of copper in the inner layers. By the time you get enough heat into one end of the lead to melt solder all the way through the via, you may well remove the outer pads. I recently replaced all the large electrolytics on a mother board just as you describe. I ended up preheating the board with a hot air gun till it was at about the boiling point of water (put a drop of water on the board near the joint being worked on and wait for it to start to bubble), before applying heat to both leads with an iron heating a big blob of solder. Harder than removing the caps was the process of cleaning the holes well enough to insert the new caps. This also needed the preheat and a length of stranded wire I used as a solder wick. Soldering the new caps in required preheat, also. Using low temperature solder (63%tin, 37 % lead or 62% tin, 36% lead, 2% silver) is very helpful. By the way, to make this process worth while, be sure you have a good grade of replacement caps on hand, or the new ones may not last long. I used the 105 degree rated, high ripple current, low ESR FM series by Panasonic, from Digikey. I was also able to put slightly larger value caps into the same space. The ripple voltage on the board was way down after the replacements were installed. The board was very unstable before the replacements, but has been running perfectly since. | |||||||||||||||||||
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Posted by w_tom on November 7, 2005, 7:47 pm
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John has demonstrated another technique that professional use - and that most anyone can do. Another factor in removing those leads is the quality of the soldering iron. Best irons will increase the heat as necessary when the load - the size of the solder joint - becomes larger. Just another trick that makes removing solder in a hole easier with less damage to the board. Also pay attention to the numbers and specs that John has provided for capacitors. John Popelish wrote: > I haven't done it as you describe, but I can understand why someone
> may have come up with that method after destroying an otherwise good > board trying to get the wires out with just an iron. The problem is > that these boards are at least 4 layers, with the caps soldered to > vias that connect to big pours of copper in the inner layers. By the > time you get enough heat into one end of the lead to melt solder all > the way through the via, you may well remove the outer pads. > > I recently replaced all the large electrolytics on a mother board just > as you describe. I ended up preheating the board with a hot air gun > till it was at about the boiling point of water (put a drop of water > on the board near the joint being worked on and wait for it to start > to bubble), before applying heat to both leads with an iron heating a > big blob of solder. Harder than removing the caps was the process of > cleaning the holes well enough to insert the new caps. This also > needed the preheat and a length of stranded wire I used as a solder > wick. Soldering the new caps in required preheat, also. Using low > temperature solder (63%tin, 37 % lead or 62% tin, 36% lead, 2% silver) > is very helpful. > > By the way, to make this process worth while, be sure you have a good > grade of replacement caps on hand, or the new ones may not last long. > I used the 105 degree rated, high ripple current, low ESR FM series > by Panasonic, from Digikey. I was also able to put slightly larger > value caps into the same space. > > The ripple voltage on the board was way down after the replacements > were installed. The board was very unstable before the replacements, > but has been running perfectly since. | |||||||||||||||||||
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Posted by Lord Garth on November 8, 2005, 7:03 am
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> John has demonstrated another technique that professional
> use - and that most anyone can do. Another factor in removing > those leads is the quality of the soldering iron. Best irons > will increase the heat as necessary when the load - the size > of the solder joint - becomes larger. Just another trick that > makes removing solder in a hole easier with less damage to the > board. > > Also pay attention to the numbers and specs that John has > provided for capacitors. > Least of which is the diameter of the replacement cap! Some boards do not have clearance. | |||||||||||||||||||
> worth an attempt at repair i am amateur solderer i have couple
> different weller irons 15w 25w 60w
>
> I read somewhere about cutting the caps in half and exposing the two
> cap posts then soldering new caps to the posts instead of trying to
> completely remove and replace the caps
>
> Is this a bad idea ?
> is there a good reason not to repair this way ?