Replaced the BQ24780 & MOSFETs, Still No Power? The Hidden "Fake Short" Loop!

In this video, we tackle a completely dead HP ZBook 17 G3 (Motherboard LA-C391P) that was stuck in a frustrating power loop. The board was drawing a 70mA spike and instantly dropping to zero.

Initially, it looked like a classic main rail short or a bad charging IC. I had 0V after the first MOSFET, the Embedded Controller (EC) was pulsing on the thermal camera, and the BQ24780 was rapidly pulsing the MOSFET gates. However, even after replacing the BQ chip and the first two MOSFETs, the exact same fault remained!

Using the oscilloscope, I captured the exact moment the BQ chip aborts the power sequence. It turns out, there was no short circuit! The brand-new replacement MOSFETs had a lower internal gate capacitance than the factory originals. They were turning on too fast, causing a massive inrush current spike that tricked the BQ24780 into thinking there was a short circuit, throwing it into a continuous protection "hiccup" loop.

To fix it, we modified the factory RC snubber circuit by adding a larger capacitor between the Gate and Source of the first MOSFET. This slowed down the gate charge, eliminated the inrush spike, and brought this massive workstation back to life!

#RightToRepair #BoardRepair #LaptopRepair #Electronics #Oscilloscope #BQ24780 #MotherboardRepair #Soldering #HPZBook #TechTroubleshooting

Видео Replaced the BQ24780 & MOSFETs, Still No Power? The Hidden "Fake Short" Loop! канала BoardRev