I have read this topic with interest. I purchased my NAD c390dd in 2012 or so and after a couple of years it started showing this issue. When warranty expired in 2017 it completely stopped working and from then I sank a lot of money into repairs (main board, PSU 2x), and the same issue keeps resurfacing.
It starts with occasionally not starting up with a black screen, to gradually always not starting up properly. When it does start up it does sound great (although not as good as my new Arcam SA30). It is now in use as my second amp in my home office running a pair of B&W 601S3 loudspeakers, which is quite ridiculous comparing the cost difference.
After the 3rd repair (after finding pieces of exploded capacitator inside) it has ran quite flawlessly for another year or so, now giving the same shite.
It frustrates me that nothing seems to be wrong with the other components, except this, which is then being solved with new **** components.
I am not an electrotechnical guy that has experience soldering and replacing capacitators, but it frustrates me that this limitation may require me to trash this piece of junk, which would otherwise be cheap to fix. This is the 3rd time at the crossroad of thinking should I trade it in for whatever it is worth, or should I sink more money into this sinkhole.
Knowing what I paid for it initially makes me hesitant to just write it off, but sinking in 100's every year to extend the lifespan another year is not my preference either.