after the rectifier bridge there is an big resistor, on my inverter this is from 620 kohm. this is connected between the first stage and the second stage. i found it broken, after the replace the inverter is ok

 

It works but output voltage is too high...255V and it should be 230V (240V max)

 

you tried it with the scope?

 

output voltage is too high...255V and it should be 230V (240V max)

A normal DMM on the AC range will probably give an inaccurate reading when fed with a 'modified sinewave', since it is expecting a true sinewave. A scope will give a better indication of the output voltage.