T520 ERROR CODE 21.10 UNABLE TO CLEAR

[DON CZERNY]

i had problems with aftermarket ink carriage in printer. they leaked.

i replaced them with original HP cartridge and cleaned service station- it did not help.

I ordered new service station - same problem.

ordered and installed new control board for service station - same problem.

In general after running self test for printer results are  :

 service station test - error 21:10

pump test - no noise during test cycle

main board green lite is flashing.

Help  , please