Replacing a Fragile Video Connector on a Laptop Motherboard
The Laptop was a Dell Inspiron 1750, a very nice 17″ laptop with an intermittent video problem. My first thought was to change the video cable, which had no effect. I noticed, however, that slight movement of the cable near the motherboard connector caused the picture to appear, as would slight pressure on the connector. I searched carefully but could not find a dry joint After much thought, I decided to try replacing the video connector. My feeling was that if I was wrong, the fault was almost certainly a video chip BGA fault, and I do not believe it possible to achieve a permanent repair of this without proper equipment. It may be noted that there was always a steady picture from the VGA socket. Heating the video chip did not cause the picture to appear on the main screen by the way.
I have carried out the difficult task of replacing surface-mounted video connectors before on other laptops, but never the IPEX-CONN40-2R-GP 20.F1093.040 used in this series of Dell laptops, which is particularly fragile. I have also replaced connectors with through-board pins with the same basic approach. The basic problem is temperature; the plastic used in connector constructions melts at a lower temperature than solder, and if the plastic even gets slightly soft, the connector can distort and become unusable.
An Atten 848D hot air rework station was used for this task. Many will say you can do it with a soldering iron, but I found, after many attempts in the past, that I simply do not have the manual skills to succeed. With a hot air gun and care, I can do it. It is important at this point to say: do not attempt anything like this on a valuable motherboard until you are satisfied you have mastered the techniques to do it with soldering iron or hot air gun. Practice on some cheap scrap motherboards – they all have plenty of connectors!
The first job is to get the old faulty (?) connector off the otherwise working motherboard. In principle, for this motherboard, we don’t care how much damage we cause to the connector, providing we do not damage the motherboard (in particular the tiny connecting traces), or the other components on the board. In order to protect the board we apply heat-resistant adhesive tape to the board in the vicinity of the connector, on both sides as shown in the two photos below:
This has the additional duty of preventing other components from falling off the board should their solder reach melting point. The board is mounted vertically as shown below, so that as soon as the connector solder melts it will drop off the board. Do not be tempted to prod it to help it come off – you are almost certain to lift or break the traces or pads if you do.
Apply the maximum heat from your hot air gun directly on the connector, particularly at the ends and along the back where it is solidly soldered to earth pads, as shown in the photo. The next photo shows the removed connector after it had dropped off the board – completely wrecked, but the board traces are fine!.
The next job is to find a cheap scrap motherboard with the correct connector. In my case it was a Dell 1545. In principle, it doesn’t matter what damage we cause to this motherboard and its other components, providing we get the connector off it without damage. We must therefore heat the connector from the other side of the motherboard. In order to concentrate the heat in the right place, where the solidly soldered earth pads are, mark their positions on the back of the board by measuring from the board edges. With this board, there is an unused iTPM socket on the other side facilitating this, so we can clearly see where to direct the heat.
It is also important that the connector drops straight off without any bending forces, so we mount the board upside down so the connector will drop straight down when the solder melts. In addition, we fit the video cable connector to the board connector socket. This helps as a heat sink for the plastic, provides support for the connector structure and adds a little weight to encourage a direct drop off when the solder melting temperature is reached. The photos show the board supported upside down clear of the table, ready to be heated, and the connector, still attached to the video cable, after it had dropped off.
After the connector has fully cooled, the video cable can be removed and the socket inspected.
If all looks OK, replace the video cable in the connector and check continuity. Again, if OK, you can now remove the video cable and solder the replacement connector to the original motherboard. For this, I do resort to a small soldering iron. Clean the pads on the board and place the connector in the correct position. Use a generous piece of adhesive tape to hold it in place then use a magnifying glass to check all the connectors are in the correct position on their pads and traces. Tack the pads at each end with a little solder, then recheck the traces. If all is still in position, remove the fixing tape and solder the pads along the back of the connector. Re-check the traces. Then solder the end pads properly, and finally solder the traces – fiddly job this! Be careful not to leave high blobs of solder on the pads or the cable connector will not be able to fit fully home.
Now refit the video cable to see that it fits properly and recheck continuity. All OK? Now remove the protective tape if not already done (might need some adhesive remover) and clean up any residual flux etc. Job done. Well, did it solve my problem? Well, I’m afraid it didn’t! So, I am still scratching my head. Never, mind, it was a challenge and gives me confidence that such jobs are feasible, even with such fragile connectors. Any feedback from more experienced technicians out there would be much appreciated.
This article was prepared for you by Gerry Millward from Bristol, England. He is 74 years old and retired 11 years ago as a Electronic Systems design engineer in the Defense Industry. He now operates a one-man Computer Technician business, mainly to keep himself constructively occupied. His main interest is motherboard level repair but is regularly and infuriatingly diverted to fix Windows problems.
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