DC-in/sound module, or logic board?
I picked up a MacBook Pro parts machine. The DC-in gets a light, and when I hit power the first time, nothing happens. When I hit power the second time, the sleep light comes on, the machine does not chime, and the screen does not come on, although the HD does spin. External video does not work in this state. There was a SINGLE instance early on when the laptop DID chime, and the screen DID come on, but I haven't been able to reproduce that. I imagine it's possible external video may have worked if I'd tried it then, but again, I haven't been able to reproduce it powering on successfully.
The question is, is this most likely the DC-in/sound module, or the board itself? I tried replacing the DC-in/sound module with a bad one I had lying around, hoping it would at least behave differently and give me some hints, but it behaved exactly the same.
Personally I'm leaning toward the DC-in/sound module being the issue, but before spending $70 on the part, I wanted to see what everyone thinks. It's odd that powering on takes two tries...I wonder if the sleep light and hard drive coming on are signs that the logic board is alive, or if those are DC-in/sound card functions that can happen despite the board. Is there a way to test the board itself? Based on the damage, the machine seems to have been hit really hard from underneath on the left side. I've replaced the lower casing, and neither the DC-in nor the logic board show any physical damage, although the topcase, screen, and lower casing were a total mess.
Thanks in advance!