Roxas, Isabela - Fixed, Rain damaged SNAT 3KW 24V inverter P3

2025.10.24 - From Oct 3rd to the 24th, It has been about 3 weeks that went by. Parts were ordered and they arrived so one went thru the process of removing and installing the new parts. As with things, one would hoped that the inverter would work after replacing the bad parts but it still did not work thus one was forced to continue diagnosing the circuit board. It does bring memories that were left buried, into the forefront of reverse engineering a circuit board. Quite frankly, I pretty much reversed engineered the inverter mentally

More Diagnoses
It turned out a gate resistor was damaged, along with sensing current resistor that I didn't think would be badly damaged by rain, but who knew eh? To get the darn thing to power up, one has to do this and that and it powered up eventually.

Damage so far
PWM driver UTC 3845E
MOSFET IRF 640N and associated gate resistor 22 Ohm which limits the pulse current from Drain to gate caused by parasitic capacitor.
Sensing resistor 0.1 Ohm - Studied the character of the PWM chip so I immediately understood why it still didn't work. Once that was replaced then it immediately works, yay!

AT this point E02 went away once the 0.1 ohm was installed. Using a 0.18 ohm changed the design criteria unknowingly which is telling. Using a 0.18 ohm changed the power ability to maintain regulation when under load.

At this point the high power MOSFET are not needed to be replaced. Anyway, it was fun a minute to figure the fault mode and how it got fixed