Oxygen Percentage only 30%

how are you verifying the O2 output? 

I use a Salter Oxygen Concentrator analyzer. I have calibrated it and it does work fine on other concentrators.

Salter Elite 2 Concentrator Indicator

is the unit alarming low O2 or is this purely based upon your analyzer?

if the unit isn't alarming, but your tester says it's no good. I'd question the validity of your tester. 

if it is alarming, then I would suggest checking the intake filter, the main valve, maybe it's not switching between sieve beds or allowing enough intake. 

after that, the valve b/w the sieve beds and the product tank, the product tank itself, anyone of the check valves, and the bacteria filter

It does alarm after a few minutes of operation. Pressure is cycling, no change with changing filters. I suspect its the sieve beds themselves, maybe moisture contaminated. I have ordered a new sieve canister assembly

It does alarm after a few minutes of operation. Pressure is cycling, no change with changing filters. I suspect its the sieve beds themselves, maybe moisture contaminated. I have ordered a new sieve canister assembly

It does alarm after a few minutes of operation. Pressure is cycling, no change with changing filters. I suspect its the sieve beds themselves, maybe moisture contaminated. I have ordered a new sieve canister assembly

Do you solve this problem?

I think is O2 sensor if you give low o2

he's getting the O2 alarm on the unit and his external testing device is confirming the low O2 output. it' snot a snesor issue unless both sensors are bad. It's more likely a leak or closed valve issue

Sigh so i think now that it is the control board, as really its the only thing that hasn't been replaced - new compressor, new sieves, new valves and no change.