Hi members , hope you're all well and warm ..

I normally repair the mecer 2400VA Inverters,  usually the basic IRF1407/3205 mosfet  and the 3525A dip ic ,  or IRF740 , those common blown components.

This one particular inverter has me stumped for a few days now.  As soon  as I power on with just the 24v test batteries connected ,it shows 307 volts , drops to 290 then shows a fault.It was working fine before  , sold it to a client and he returned it two weeks after . The IGBTs were blown and the two resistors next to the transformers .(can provide pics of the board )

So far I have replaced all mosfets,  all IGBT , all capacitors , SG3525A ic , all transformers but the fault persists.

Could it possibly be due to programming/calibration ? There is another IC near the communication connector.

@BritishRacingGreen & @Coulomb should be able to assist

This is a sample of the IC/cpu I was referring to, will remove one from a donor board and fit  (hopefully not damaged ) then see if there's any change 

I'm pretty sure that these are the same as the 8-bit processors used in the very low-end Axperts and also some of the low PV voltage solar charge controllers.

But I don't know anything about these Lobos, not even whether they are made by Voltronic.

Thanks all, I've changed the processor and still get 300 + volts , will keep trying and post if I make any progress.