Hi, John,
thanks for the tip. I think you mean L503 (the one between Q508 source and ground). I checked two ways: L503 end-to-end, and Q508 source vs ground (at the power supply connector, there it is easy to reach). Both show 1.8 ohm at 200 ohm range of my multimeter.?
So it looks like replacing Q508 - the diode is OK but the channel seems to be interrupted. It's not even that the drain pin were cold-soldered, the MOSFET is broken...
Another question is how this could happen. An internal "spark" between the gate and the channel that would vaporize part of the channel??
Anyway, everything was fine when the battery voltage was 12 V or below. When I connected almost fully charged battery, the MOSFET failed (and I hope it's only the MOSFET and not something else down the path).
BTW, is there any significant difference between 2N7002 and BSS123?
Jindra
