Picked up a second hand RNS510 as spares or repair dirt cheap. It was really only to replace a dvd drive in my spare unit, and rather than buy just a dvd drive I got the whole unit for half the price of the cheapest second hand drive I could find. So, pinched the drive out of it and installed it in mine, and all fixed. Then I thought I'd have a look at the other one.
Stripped it a bit, and found this...
Would you think that's the problem?...