(come to think of it, the same is true for pretty much any electronic appliance, isn't it? :-)
Well in case of the NS-L42Q-10A and its sister NS-L42X-10A it is rather likely that it's the power board.
I've seen few of those already and they all had similar problem - lack of the standby 5V power and everything else from there on.
The power board's model is 715G3196-1 and it looks like this:
The problem was relatively easy to spot on the first of the boards and a little more obscure on the others.
It was the SMPS driver IC IC901 that was burned. On some boards it has shorted and that did burn a few other components in the circuit.
On some it was apparently burned open and although maybe a bit overheated the other components had survived the failure.
Based on those experiences we've assembled a simple repair kit containing the components that are most likely and usually burned - IC901, ZD906 and R950.
This blog is hopefully useful in confirming that this seems to be a common problem for this board and naming the components you need to pay attention to.
Granted, over time it may turn out there are other problems as well. We'll update the blog if and when we know more.
In the meantime, you can try and source the components by yourself or you can use our kit for what we consider a quite reasonable price.
And if you don't feel like doing that by yourself...you can always contact us and send the board for repair service at Coppell TV Repair!