sounds like a PSU issue. I have a Corsair C600M with 552W of 12V power and it ran an overclocked antminer without problems. However, not all power supplies can push full capacity for 24/7 and some may not be able to hold more than 80% of the peak rating for a long time.

Try disconnecting power from the secondary blade and try again. If the device runs 90GH without problems but is having issues with running both blades then its a PSU issue