Hi Bill,   You might shut the MD chassis off, then swap the power supplies around. This would let you isolate the PSU from the slot. However, if you were testing the suspect PSU with it isolated from the MD and still seeing this behavior, then the PSU would be the issue. From my read of your post, it sounds like the PSU is the problem.
Greetings, I have an MD1220, and one of the power supply indicators is out. The bottom indicator ("AC Power") is lit, so I know I have power coming in to the unit. The middle fault indicator is not lit, so no problems there. The top LED ("DC Power") is NOT lit, which seems to indicate the following: If this LED is off, it indicates that the DC output voltages are notwithin the limit. The Modular Disk Storage Manager software has the following error:   So, while power is being supplied to the unit (it is plugged in) the MD1220 doesn't like it, and thinks it's not plugged in (even though the "AC Power" LED is normal). So my question is, does this indicate that the power supply has failed and needs replacing, or could this be something else? Note that this was all working correctly until I had to shut everything down for UPS maintenance.  When everything was powered up again, this issue presented itself.  I've tried plugging the power source into other sources (even direct into an outlet) and that changes nothing, so it's not an issue with the UPS or power source from what I can see. Thanks, Bill
PowerVault MD1220 "DC Power" Indicator not lit