Tricks to replacing motherboard fuses?

My laptop suffered a blown fuse and the backlight no longer works.

It's a common problem for my make/model and I'm piecing together the information to attempt a repair.

The fuse is the "Littelfuse" variety, 1206 32V 3A and shows no continuity.

As I don't really have professional equipment, aside from bridging the fuse with some solder, I'm thinking I might stack a replacement right on top and "replace" it that way.

Any advice or thoughts oh how this repair could most expediently be effected are most appreciated.

Edit: I caused the fuse to blow by not removing the battery while replacing the lcd. Stupid to think the power button was enough! A mistake I won't make again!

Alex Kessaris

Posted 2015-04-30T22:23:44.223

Reputation: 121

2The real trick is finding out what had caused the fuse to blow in the first place. – Nick Alexeev – 2015-04-30T22:31:45.030

@nick-alexeev, reason added.. – Alex Kessaris – 2015-04-30T23:15:13.250

3Use two soldering irons at the same time to remove the old fuse. It is much easier this way. I assume you can put the new fuse in OK? Watch a video or something. 1206 is pretty big. – None – 2015-05-01T00:23:52.967

Answers

It's possible to remove it with one soldering iron. Add some extra solder to the pad at each end, the extra metal will retain heat longer. Go back & forth quickly with the iron, say 5-10 seconds each end, until both ends are molten at the same time. Apply gentle pull with tweezers at the same time, and when both ends are ready it will come away from the board.

You might heap enough solder on the part to bridge the two pads, so you have only one blob of solder to melt. Once the part is off the board, clean the pads with solder wick.

Alternately, the fuse is probably brittle and may crack in half if you push down on the middle of it. Then you can unsolder one half at a time to remove it from the board. Be careful not to apply so much force to the board that you damage traces or nearby components.

Matt B.

Posted 2015-04-30T22:23:44.223

Reputation: 156

2Trying to crack the fuse is an invitation to disaster if the fuse is indeed on SMT pads. I can say from practical experience that doing any attempt at breaking, cutting or cracking components can put huge forces on the pad and rip them right off the board even if it looks like it would not. So use extreme care. The best solution is a tweezers type soldering iron. The second best solution is two soldering irons. – Michael Karas – 2015-05-01T04:41:20.033

1Depending on how many components in close proximity to the fuse may suffer from high temperature and accidental contacts with soldering iron, I'd say bridging the old fuse with a new one on top may be a sound option. – Dmitry Grigoryev – 2015-05-01T07:10:16.100

Littelfuse is a manufacturer of fuses. The fuse can be replaced with any common soldering iron (smaller tip the better) as it likely isn't on a large copper plane. You can get the same type or similar fuse with a little searching. 1206 sized components are big enough that they are no problem to anyone with even a minimal amount of soldering experience. _{I have 1/8th Watt resistors that are physically smaller than 1206 surface mount ones.}

cde

Posted 2015-04-30T22:23:44.223

Reputation: 1 665

1"smaller tip the better". Not entirely true. You want one around the 1mm mark. If it is too large then it can be difficult to get it onto the solder joints if there is lots of other stuff packed too close. But if you go for a very small tip, e.g. 0.5mm or even 0.2mm(have one of those), then you'll never get the thing off as the boards tend to be multilayer with power planes and you simply can't get enough heat into the board to melt the joints. Also as you are desoldering, add more solder on as it will help the original solder flow better. – Tom Carpenter – 2015-05-01T02:50:18.177