I have a phoenix multiplus 12 2500 120 inverter charger and it has a problem where when it is switched on it goes straight to a solid overload light with no power output. The output is disconnected so no chance of an actual overload. The 12v battery is fully charged. I've taken it apart and can't see anything wrong. Checked all fuses and they are okay. I can't see or smell anything burnt on the PCBs or transformers.
Its a fairly old unit, I was wondering if a firmware update would fix it.
Any help would be appreciated