Hi Martin,
Both PCI-6225 and PCI-6704 needs 12V to operate:
PCI- 6225 Power Requirements
Current draw from bus during no-load condition
+12 V.......................................... 0.15 A
Current draw from bus during AI and AO overvoltage
condition
+12 V.......................................... 0.25 A
PCI-6704 Power Requirements
+12 V...................................................... 70 mA
In your system those two PCI-cards will need min. 220mA at 12V rail to operate, so 400mA at 12V rail for the entire system doesn't seems to be enough.
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Dennis Morini
District Sales Manager
National Instruments Denmark
http://www.ni.com/ask