While you have the unit open, move the drives/cable around to see if it spins up/down. A bad cable and not simply a bad connection can make your drives come on/offline at seemingly random times.

I bought my MK2a recently and the drive cable was bad. After first playing with it and adjusting, the unit worked for a while. But moving the tray assembly around could cause it to stop. A new cable sent from empeg fixed it all up.

Bruno