PI1000BN Inverter problem

I have a PI1000BN inverter and the fault light comes on nearly every time I switch the unit on despite the voltage being 1000% within the acceptable limits. Is there anyone who can direct be were I can get the schematics for this Velleman Inverter. Please note I am more than prepare to pay for this.

Please: Velleman Projects items only (see forum rules).
For all other products of the Velleman Group, please use the online support form:
velleman.eu/support/contact/?product=350602