Oxygen concentrater has very low output

I have a used invacare platinum 10 I recently purchased. When I turn it on there's no error beeps or any other signs of an issue. However, no matter what position the output dial is in it will only output ~0.5 lpm. The filters all look good and I took the cover off and ran it to look for any leaks and everything seemed in order. Any help or suggestions would be greatly appreciated. thanks!