A couple days ago my Dell SE198WFPV monitor started turning itself off and on at random time intervals. While this was happening, I also started hearing a strange buzzing sound coming from near the power connector. So I took the thing apart to see if there's anything obvious like a failing cap or other burn marks, but I didn't see much. But I did notice that the buzzing sound came from the yellow SMPS transformer, and one particular heatsink got so hot that I burned my finger on it.
After some digging, I found the source of the heat to be a AP2761I-A power MOSFET on the heatsink, and I'm hoping that this component is the root cause of the problem. The closest donor I have is a ST-12NM50FP that I salvaged from an old projector's PSU board. When comparing the two sheets side by side, most of the important specs seem close enough, with the biggest difference being the zener type diode. Other than that, the donor has a slightly higher current rating (Id=12A instead of 10A), and a lower gate resistance (RDS[on]=0.35Ω instead of 1.0Ω).
I think the overheating MOSFET is definitely the main problem here, because if I turn on the monitor, it does work just fine for about 30 minutes, and I don't even hear the buzzing at the beginning. But then the PSU overheats, and the monitor goes into a reboot-loop.
Is it safe to replace this component as a troubleshooting step? Or is it more likely that the faulty component is the SMPS transformer and the whole monitor is basically useless?
AP2761I-A:
https://alltransistors.com/adv/pdfview.php?doc=ap2761i-a.pdf&dire=_apeST-12NM50FP:
https://www.mouser.com/datasheet/2/389/stb12nm50-955456.pdfA pic of the PSU: