False 3T 16 (sixteen) Channel Switch diagnostic failures seen from ports connected to "A" and "B" connectors.

False 3T 16 Channel Switch diagnostic failures seen from ports connected to "A" and "B" connectors. See Long Description (from SMILe 8/23/05). Effectivity: All upgraded and installed 3T Signa EXCITE HD MR systems. Problem: The 3T 16 Channel Switch Diagnostic may report false failures on one or more of the 8 receive lines on the input J21, "A", and J22, "B", receive ports on the 3T 16 Channel Switch. These false failures, by themselves, make it appear that the failure is inside the 16 Channel Switch. The remaining ports do not report false failures. It has been determined that the test oscillators inside the 16 Channel Switch can introduce RF reflections on the cable-track cables that connect to the "A" and "B" connectors inside the LPCA. Since the diagnostic is normally run without a coil connected to the receive lines, the lines are not terminated with a load impedance. This situation allows reflections to develop on the lines. The reflections, if strong enough, can affect the test signal and thereby cause a false failure of the 16 Channel Switch diagnostic. This effect is only seen on 3T systems since the RF wavelength of the test signal is short relative to the cable length. Other factors such as cable length, type, and positioning affect the magnitude of the reflections so the failure will not be seen on all 3T HD systems. The conditions that permit reflections to exist are only present during the execution of the diagnostic and are not present during normally scanning.