Help soldering on a multi-layered board - Page 1
Forum section: electronics / beginners

author: maxwell
author_rank: Newbie
timestamp: August 07, 2010, 04:21:49 pm
content: Hi all,I was just wondering if I can pick your brains as to how to go about fixing a little problem I have with an RJ45 socket connector I am trying to resolder. I have recently purchase a second hand IBM x61 laptop off ebay and found that the LAN port does not work. So of course I opened it up to find the connector's joints on the mainboard PCB looking not so good and possibly like someone had tried soldering the connector previously without success. The laptops lan works fine using the docking station so I know from the schematics that everything is working up until the last IC, responsible for switching between the docking station and the onboard RJ45. So between that IC and the RJ45 socket there seems to be a problem. The PCB joints look terrible as you can see in the photos. They maybe a little worse than when I found them but not by much. Two of the pins in the fist photo seem to not have any pad to solder to. So the issue is that I cant seem to resolder the connector as is. The holes in the board dont seem to want to fill and i'm not sure being a multi layered board if there is a trick to this. Is this beyond repair? I would trace each pin back but being a laptop and a small one at that seems to make things rather difficult. Any help would be most appreciated.Due to the image limit, I have put more images/schematics etc onhttp://fullof.info/x61

author: DJPhil
author_rank: Frequent Contributor
timestamp: August 07, 2010, 04:27:09 pm
content: It looks like it needs a good cleaning. Hit the area with some rubbing alcohol and a toothbrush to clean out all the dirt and funk. The joints that are there are bulging, which is a sign that there wasn't enough flux to properly wet or clean the metal underneath.If it were me I'd clean it, use a flux pen and solder wick to pull out what's there (don't have to get it all, just most), clean again, flux again, and resolder.Hope that helps.

author: Valhallasmith
author_rank: Contributor
timestamp: August 07, 2010, 04:40:09 pm
content: And if you find that re-soldering doesn't work then you need to trace the pin back to something you can solder to. Run a thin insulated wire between the ethernet pin and where it should connect to something else.

author: djsb
author_rank: Super Contributor
timestamp: August 07, 2010, 05:10:50 pm
content: You may find this link usefulhttp://www.circuitrework.com/guides/guides.shtmlDavid

author: Pyr0Beast
author_rank: Contributor
timestamp: August 07, 2010, 05:48:45 pm
content: As a note. Docking station usually has its own integrated LAN card.What I think is that connector was actually removed because of the extensive damage. Is it 100MBit or a GB card ?I would clean that burned flux first. Cotton swabs and acetone would do.It seems a capacitor or resistor was sheared off as well.Clean the solder with solder wick or desoldering pump and apply fresh and good one. Also, board needs to be preheated - use hair dryer until it is hot to touch.Once it is done, fix the connector with hot glue.

author: maxwell
author_rank: Newbie
timestamp: August 07, 2010, 06:26:42 pm
content: Thanks for the comments so far. Its very helpful. I would add the other schematics but there is an image limit.Pyr0Beast, there appears to be three potential LAN I/O's from a GBE LAN switch on the laptop mainboard. Only the first two are used, one for the on-board LAN and the second for the doc LAN. There is a dedicated Dock Connected? pin to determine the current state of if you are using the doc or not.I'm going to pickup some flux and completely re-solder the socket I think. As well as replacing the surface mount capacitor that came off. My soldering iron is temperature controlled but not the best (cheap ebay job) but I think the suggestion of flux is a good one. Its not something ive used before but I think it sounds like the go. Where do you get replacement surface mounts like that? I guess I will need to replace the missing capacitor from somewhere.In the PCB holes for the RJ45 connector, some pins do not have tracks either side but I know they are connected just from the LAN PIN definitions. With a multilayer board like this would there be tracks between each side of the board (layers in between) connecting these pins and if so is there a trick to getting the solder to stick inside the hole? I found a few of the pins would not take any solder on the initial inspection. If I unsolder the RJ45 and then clean with a solder sucker and then some acetone. Then use flux before solering? I'll try a hairdryer as well if I can find one.Thanks for your help, really appreciated.Just a note, due to the image limit I have put more images/schematics etc onhttp://fullof.info/x61

author: DavidDLC
author_rank: Frequent Contributor
timestamp: August 07, 2010, 07:12:43 pm
content: Your other option is to buy a PCMCIA LAN Card, they are now really cheap.Ebay will be an option to get this card even cheaper, I can see now some of them incredible cheap !

author: RayJones
author_rank: Frequent Contributor
timestamp: August 07, 2010, 11:19:10 pm
content: That mess is reminiscent of a lightning strike with all the apparent carbon scoring.Either that or a blowtorch was used