I was very lucky buying two months ago a not working Lynx II. It had only dirty contacts on all the 4 carts coming with it and a dpad stuck on right direction (still have to fix it, but sould be only a dirty contact).
Some days ago bought a Lynx I for 30 € and this time there is something broken (already tryed to short the battery minus with the audio jack mass).
Probing the circuit, the +5V point and the mass are in short circuit (measured it at the ends of D14). The zener diode and the mosfet, tested without desoldering them, seems ok.
Now I should start desoldering components in the hope that there is a fault component before mickey os suzie. Or I could connect the power supply and check if there is a transistor or IC heating.
But before doing anything I'd like to know if someone else experienced such an issue, what are the most common points of failure and how to check them.