My DS416 broke. The Powersupply was okay but there was no reaction from the NAS if I switched it on. No LED or FAN. After some digging I found the cause. Capacitor C390 was shorting (get really hot). I replaced the Capacitor with an 10μF (i think). Now the NAS works like a charm (again).
(!) The Capacitor is glued to the PCB. Try not ripping pads.
The solering-job is poor because I ripped the pads and want to make sure all 3 Points (backpad, frontpad and Cap) are connected
addendum: After a couple of days the NAS stopped working again. After a fix check both caps (C390 and the cap next to it) are broken. They they seems to be in parallel. After changing both the NAS worked again.
addendum2 (month later): The next cap died. This time it was C150 – found on the underside near the power-connector.
You just saved me hours of work. I had the same issue and replaced with .1uf 50V smd’s. It’s what I had on hand. THANK YOU!