Varian CP-4900 MicroGC Channel 3 shows -554.7 Autozero value. It has been suggested the TCD may be dead. It reports no signal, however the other two TCD's report less than 50 Autozero and work fine. The marketing images for these systems suggest the separate GC channels are swappable. Is this so? Would I be able to swap TCD's between channels? Channel 3 is the most important for our application.