FX2024WT output waveform

[Seedywee]

Installed in 2014, my FX2024WT inverter died from a lightning strike in 2016. After all three PCBs were replaced, the output looked like this:

This inverter is still in continuous use but a recent oscillograph shows the output as:

Is this healthy? If not, what could be wrong? Thanks!

24Vdc utility backup system: 2 pcs Trina 72-cell 325-W poly panel, 2 pcs Trina 150-cell 500-W mono panel, 2 pcs Lumiax MT4010-BT controller, 8 pcs Higee 120Ah LiFePO4 cell, JK BMS, Outback FX2024WT inverter.

[Seedywee]

It has been determined that the strange waveform occurred because a small stepdown isolating transformer was connected for safety between the mains and the oscilloscope. The "envelope" shapes in the waveform were caused by leakage inductance in the transformer.

The problem was cured by placing a 10W load resistor on the secondary of the transformer.