So, just wanted to add my first measurements:
it seems that the 3.3V regulator doesn't deliver enough power. Testpoint J302 only gives app. 1.8V. The DC-DC Regulator U300 gets it's 5V from the 5V regulator circuit (testpoint J303 shows it correctly and the 5V are also present on Pin 1 of the U300).
So my guess is that either the 3.3V Regulator (U300 is a LM3674) is broken, that some part within the 3.3V circuit is broken or that a device depending on the 3.3V is broken (the load would be to high an the security circuit of U300 limits the output).
I've seen that the 3.3V are needed for the USB controllers and the Main CPU. So there is nothing one can do if these have a problem. So I measured the resistences in the 3.3V regulator circuit. But in difference to the circuit scheme R303 doesn't show the 536kOhm but 84.7k and R305 has no 100k but also app. 85k.
I looked into the datasheet of U300 (or LM3674, which is right in my case, it has "SLTB" on the chip and only the LM3674 and not LM3671 has these) and there you can find that 536k and 100k are really needed if one want's to get 3.3V out of the 5V at the input.
So my question is, do I miss something here or is it really possible that resistors can get broken without doing something to the unit? Maybe Matt can help or say if a similar problem occured with the 3.3V regulator.
Thomas or "kasi"