1、check the U1930 grounded ok
2、check pralink state, it's ok
3、check the clock sources, it was configured
4、check LMT Alarm infomation， there is no related info.
5、we found there is only one E1, and our R&D told me that when there is only one E1/T1 , U1930 will think another E1/T1 connection is not oK, so the LOS light will always show yellow.