@ Pooh Bear

On a *new* unit ? I assume you don't mean actually brand-new.

Ok, not clearly defined - my new acquired pre-amp.

This is fixed so I can feed the unit with 12V AC
on all inputs and it works.

Caught twice:-)) Meant the internal inputs

Sounds more like a PSU problem than transformer.

Sorry for my bad (technical) english - meant the PSU = transformer

Why not measure the transformer secondary voltages yourself ? Either they
will be right or open circuit.

Transformers don't go slightly wrong voltage.

But they could be destroyed - like in this case. So the output is on all wires 0

Wolfgang