Solar inverter does not detect panels after fixing error code 09

[PVguard]

After fixing error code 09 (DC bus soft start failed) by replacing a few MOSFETs and IGBTs, the solar inverter stopped detecting solar panels. I checked the voltage at the fuse (before and after) and at the end of the cable. In all cases, it read 400 V. But Immediately after connecting the cables to the inverter, the voltage dropped to 0 V. Other parts of the inverter are working: it detects the battery and mains.

The inverter worked completely fine before the code so I suspect the inverter and not the panels.

 

[SeaGal]

Sounds like either a high resistance somewhere in the PV circuit or within the PV part of the inverter, or a short circuit in the inverter. Have you measured current flow when the voltage drops down? That would help narrow down the possibilities.

As you mention a fuse does that suggest you have parallel strings?

 

[PVguard]

I can't measure current because I don't have a clamp meter.

If you mean solar panels, they are in series.

 

[Solar Guppy]

There is a lot more to repairing complex electronics than replacing MOSFETs and IGBTs, at a minimum the gate drive circuits usually get damaged or much worse.