Hi having a issue with a Definity Audix R4 slim that randomly stops working, when i log onto the system and run tests the only error that i can find is the when running "test board" the teat that fails is the "Test UART with the fault code F DSR-INACTIVE for 01B1801 and 01B1802, i have looked through all my maintenance manuals for this code but have so far nor been successful. can any of you old times shed some light on the issue and would anyone know where i can send the unit to in Asia or the States for repair if required