Just to clarify, are you using a step-down transformer? the system only runs on 110v unless there are specific parts changed to accommodate 220v.
the system does not step down the power on its own without a separate AC input and isolation transformer that are ridiculously overpriced from Siemens, which leads us to selling our Aspens with external step-down transformers.
as for the 5vdc and the MDI... it is a very touchy power supply and if anything is missing it tends not to work. the 5vdc not being present would indeed prevent the system from booting on, it could be something simple inside the power supply unit, but I have not personally troubleshot it down to that level, we use a third-party service company to fix our units for a nominal fee.
we could always try shipping you a power supply module, at your cost, and if it works then we could do an exchange on the power supply. if it doesn't fix your issue, there will be no restocking fee, we would just need the return shipping taken care of. i hope you can see that as a fair arrangement.
Universal Diagnostic Solutions