Drives won't turn on

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Back in August, we had Zeiss in to look into the "shaky" VAST-Gold issue we had on our Prismo Ultra.  When the tech started working on the machine, the drives were off, but couldn't be turned back on from either the joystick box or the controller unit.  We re-stared the cmm but the drives still wouldn't turn on.  We powered it down and let it "cool off" for about an hour, re-started it and the drives came back on. The tech suggested it sounded like it could be the controller mainboard since the drives couldn't be turned on in either location.  He replaced the controller board and everything seemed to be ok. 

This past Monday, it happened again. This time, the drives came back on after a quick re-start.  As luck would have it, Zeiss was due in later in the morning to do a calibration.  This tech said it there are cards on the controller card that were probably not changed when the mainboard was changed and could be causing this issue.   Has anyone experienced a similar issue, which is has been resolved?