The two controllers in each Junctor Frame had no-test access to their Junctors via their F-switch, a ninth level in the Stage 1 switches which could be opened or closed independently of the crosspoints in the grid. When setting up each call through the fabric, but before connecting the fabric to the line and/or trunk, the controller could connect a test scan point to the talk wires in order to detect potentials. Current flowing through the scan point would be reported to the maintenance software, resulting in a "False Cross and Ground" (FCG) teleprinter message listing the path. Then the maintenance software would tell the call completion software to try again with a different junctor.