Inverter fault F03 - Help troubleshooting (can't find circuit diagram)

[black se7en]

I have a 12v 2000W inverter that had been working and was generally running a fairly low load. Usually a small fan, phone chargers and some LED lights and occasionally a travel fridge. Earlier this week it was just running a small fan and it shut down with a fault F03. I never had a manual for the inverter. I believe the F03 means low DC bus voltage but not 100% sure. It's a generic pure sine inverter and I couldn't find much info online unfortunately.

At first I thought maybe the batteries were drained for some reason but they tested 13.5v for the bank. I tried a separate battery that was fully charged and still same fault. When I turn the inverter on, it shows 13.Xv on input, 0v on output, then after about 5-10 seconds it starts beeping and the protection and fault lights come on. I've tried using an external charger/power supply to supply 14.Xv to the battery/inverter but same error/behavior even though the input volt shown on the inverter shows 14.Xv.

I've opened up the inverter and have not seen any burnt components or damaged traces. There are three transformers in it and each one is receiving good DC voltage. I'm comfortable replacing components on a circuit board but not familiar enough with how inverters work to know what to check next. Would a bad cap cause low DC voltage? Which IC/component does it use to detect for low DC voltage scenarios? I don't mind by-passing the low-voltage shutdown if needed but I don't know which part of the circuit is responsible for that.

Any help or pointed in the right direction would be greatly helpful! I love to learn!

 

[sun walker]

I hope a member has an answer for you, its more plug & play for many here.
Obviously you have checked the fuses in the inverter. There are some good inverter repair vid's out there that may help, I'd be interested if you figure out the fault, be sure to post your results.

 

[wpns]

Yeah, not really seeing anything, other than the fuses, which may be soldered in place?

I used to be good at repairs, but generally not without schematics. Do you remember where you got it?

 

[wpns]

Hmm, could it be (Google Lens FTW):

Amazon.com

Edit: That's the 24V version, and my Google Fu fails me on trying to find a manual, but that might be a starting point?