concentrator woes

[franklin sankar]

I have a visionaire V airsep concentrator. Can someone please tell me where the filter is located.
I am getting a loss of oxygen sort of like in pulses. I blocked the outlet line with my thumb and the ball fell and pressure built up. so maybe no serious leak

Hope the pic attaches if not will try again.
Also any one found a repair/service manual on line. I can only find Visionaire 2,3 manual not V or 5. and the patient manual for V only not the repair manual.
I opened the front of the unit and could not find the filter.
Thanks for your help, this is driving me crazy.
Regards
Franklin