Pioneer vsx817 won't turn on

@gene29666 these are just to complex to say "go check x,y,z part and be done with it" :-) I would start by checking the power supply.

Here comes the real issue. You need a multimeter and need to know how to use it. Remember you are working with a hot power supply. That means you are always running a chance of getting zapped by some pretty good voltages. BE CAREFUL AND KEEP YOUR FINGERS ETC. AWAY FROM THINGS. Let the test probes do the touching :-).

Then you need to use something like the Pioneer VSX 817 K Service Manual Go to something like page 109 to check the power supply. As you can see by the flowchart, it is pretty complex. If you are new to checking those things, you can consider posting well focused, large images of your boards with your Question. That way we can see what you see and hopefully pointing things out to you. This will not be a quick fix :-)

Adding images to an existing question