I've had Many of these flts. Check the 24vdc power supply. I was popping L24 cards every few days at one of my jobs and went through a few LN cards too. My voltage was 23.3vdc at supply and 22.75 at the farthest card. Bumped it up to 24.75vdc at the supply and it's been good for a year now. Verify on lon explorer that you are communicating with both channels (car and hoistway).
