TRU Not Getting Busy in chgr=0

Hi,
Iam handling both IOG20 and APG40 RBSC’s,Ericcson Platform. And I want to know that,most of the TRU’s in CHGR=0 are not getting busy except the BCCH and CBCH……My TCH and SDCCH remains IDLE all the times…even at heavy traffic condition.

And if the all the cells with combined 900 and 1800Mhz Band all the TRU’s are getting busy but some cells with 900Mhz band dont…Why???

Which Parameter I should check?

Also Iam experinencing heavy call drops in those cells