Ricoh cl4000

It is working now, however I had to have Ricoh come out they cleared up the error code and told me I needed a new transfer unit and black PCU. I got both items from a 3rd party and installed them problem did not go away. I called Ricoh, they sent their guy back out at n/c and he got it going after taking much of the machine apart but he was not very clear on exactly what caused the problem.