Living Air XL 15, no ozone

Trying to help a friend. Unit was not emitting ozone, and fan was very sluggish. Replaced fan and cleaned lint filter. It now runs properly. Ozone plate didn't look dirty but did have a dark spot where contact touches plate. Replaced plate with new plate. Still no ozone. Took plate back out and turned unit on as directed in manuel, checking for Prove-it light. No light with fan running and ozone control set at 12 o'clock as directed. Also the ion indicator lamp does not light. I'm usually pretty good at following directions if you can tell me where to go from there. Thanks for your help.