1.CVBS transmit composite video signal, which combines luminance signal and chrominance signal. S-Video transmit the two signal in a saperate way, so the monochrome image perhaps is caused by transmission way selection. Check the corresponding interface of output signal and use remote control to change video output form and then the problem solved.
2.Make internal loopback under E1 transmission line and check line condition to be normal, so the terminal E1 interface card is normal.
3.Use a testing terminal which has been tested and proved normal before to check whether it is the transmission line problem. The testing terminal still couldn't join the confernce and thus draw a conclusion that there must be some problem in the office transmission line.
4.The office staff fix the E1 line and the testing terminal join conference successfully.
5.Change connection line to connect the abnormal terminal, successfully join conference and all function normal.