We wouldn’t go so far as to say “don’t try this at home”, but the way [Troy] Bringing an expensive (but out of warranty) laptop back to life is interesting, although it shouldn’t be anyone’s plan A for the repair work.
It all started with a friend’s Alienware laptop booting only on a black screen and getting very hot in the process. Using a thermal camera and some diagrams, [Troy] could see that one of the MOSFETs close to the power supply appeared to be the culprit. Swapping out power MOSFETs for replacements seemed a reasonable approach, so armed with a hot air rework station, he got to work. But that’s where the problems started.
The desoldering process was far from clean, in part because the laptop’s multi-layered PCB had excellent thermal management, sucking heat almost as fast as [Troy]The heat gun could put it down. It ended up being a messy job that damaged some of the pads. As a result, the prospects for soldering on a replacement did not look good. But examination of the diagram and reflection on the situation gave [Troy] an idea.
According to the diagram, the two MOSFETs (at least one of which was faulty) had parallel peers on the other side of the board. This is usually done to increase the capacity and distribute the heat load somewhat. However, according to the current calculations in the diagram, these parts should handle around 20A in total, but the datasheets show that each MOSFETs could easily handle this kind of current (as long as the heat sink could keep up.) In theory, the laptop didn’t need the extra capacity.
Could the laptop “work” now that the defective part had simply been removed? [Troy] and his friend [Mike] were ready to give it a try, so after cleaning up the mess as best they could, they turned on the laptop, and to their slight surprise it all worked! Some stress tests with heavy games have shown that thermal issues are a thing of the past.
Simply removing a part might not be the best overall repair strategy, but just like shrinking a hot air rework station by simply cutting it in half, it’s hard to dispute the results.