Need help with Ups/Inverter

[sarry86]

Hello everyone, I have this ups/inverter IGBT 1450VA which was working great until it started showing short circuit on a small lcd screen, I opened it up and started troubleshooting it and indeed I found some fault transistors, I decided to get rid of all of the transistors next to the shorted ones and it worked for some minutes without a problem, but then I heard a relay tripping off, and now it is showing that 2 batteries connected in series have no power at all, and if i disconnect the 24dc in then the battery are showing they are full (28vdc) with another inverter, they are working great no problem, I started to troubleshoot it again starting with the parts I replaced, they are okay, checked other included igbt (GW30NC120HD and G4PH40UD2) they're all fine, I am outta ideas, what else could be the problem here?