Shugart 851 power problem

Hi, I have a pair of 851s in a nice case with power supply. They are attached to a Cromemco 16FDC in an IMSAI box with a Cromemco ZPU and an Expandoram 64K board. I'm using the ROM enable on the 16FDC to drive the phantom line. There is a reason for these details... Here is the problem: #1 Power up the drives by themselves: At the drives: 5 volt line reads 4.9 -5 volt line reads -4.9 24 volt line reads 23.9 #2 Power up the IMSAI box: At the drives: 5 volt line reads 1.2 -5 volt line reads -0.9 24 volt line reads 2.6 and (needless to say) the drives don't work. The Cromemco ROM monitor gives all sorts of errors trying to access them. #3 Power off the IMSAI box: (Same as #1) #4 Power on the IMSAI box again: At the drives: 5 volt line reads 5.0 -5 volt line reads -5.0 24 volt line reads 24.0 and the drives work fine. What gives? Does this make sense to anybody out there?