So I gambled and decided to pick up a CIB Atari Lynx II that was listed as for parts. It's simply not powering up with either the official power adapter (DC 9v 1A) or batteries. I get nothing. I opened it up and checked capacitors and I can't find any blown fuses, etc. Any particular points on the board I should be checking for damage? Also, I hear the MOSFET transistor at Q12, which has to do with powering on the system can go bad and need replacing. I did run a wire from the headphone jack to the negative battery terminal and it still won't power on.
EDIT: I have a wire soldered from the headphone ground to the terminal and when I plug the power supply in, the screen will flash on and then immediately off. But it does seem to power on fine with batteries. Should I replace the MOSFET?
EDIT2: When I power it on via batteries, I just get a blank screen (backlight does light up). No sound/game picture, etc.
Anyone experienced with Lynx II repairs and have some ideas for me to try?