How to check which parts of a dead MacBook Pro 17" Mid 2010 work Mac was water damaged. No start up chime. Charger shows green light dimmer than when plugged in to working Macs when plugged. Battery status button on side has no effect. Won't start in safe, target disk, verbose etc modes. Removed the HDD and verified that it works fine and am cloning it before wiping, reinserting and selling. 

I believe only the logic board is broken/shorted, but what can I do to check whether anything else works? Specifically if I can make sure the display is functional I assume it is of greater value.

edit: I have on hand a voltmeter and the 2011 model of the same Mac, but do not wish to potentially break that one in establishing what works on this.
That will depend on what kind of analytical/measurement tools do you have? Oscilloscope, Volt meter ect...

Since it does not start at all and Battery is shut it could be simply the power input module. Open it and check if power is coming in and the fuse is not blown.

Is the display working: try the Target Display Mode.

Here is some how to:

http://forums.macrumors.com/showthread.php?t=1122338

Check your DCIN board.