19V SHORTING REMOVE BY EASY METHODE BY HAND SENSE CAPACITOR SHORT
It started with a friend’s Alienware laptop that would only boot to a black screen and get very hot in the process. With the help of a thermal imaging camera and some schematics, [Troy] was able to see that one of the closely-spaced MOSFETs in the power supply appeared to be the culprit. Swapping the power MOSFETs out with replacements seemed a reasonable approach, so armed with a hot air rework station he got to work. But that’s where problems began.
The desoldering process was far from clean, in part because the laptop’s multi-layer PCB had excellent thermal management, sucking away heat nearly as fast as [Troy]’s hot air gun could lay it down. It ended up being a messy slog of a job that damaged some of the pads. As a result, the prospects of soldering on a replacement was not looking good. But reviewing the schematic and pondering the situation gave [Troy] an idea.
An open laptop showing a diagnostic tool on the screen
One expensive laptop, brought back to service.
According to the schematic, the two MOSFETs (at least one of which was faulty) had parallel counterparts on the other side of the board. This is typically done to increase capacity and spread the thermal load somewhat. However, according to the current calculations on the schematic, these parts are expected to handle about 20 A in total, but the datasheets show that each of the MOSFETs could handle that kind of current easily (as long as heat sinking could keep up.) In theory, the laptop didn’t need the extra capacity.
Could the laptop “just work” now that the faulty part had simply been removed? [Troy] and his friend [Mike] were willing to give it a shot, so after cleaning up the mess as best they could, they powered the laptop on, and to their mild surprise, everything worked! Some stress testing with intensive gaming showed that the thermal problems were a thing of the pas