• If a loop reports only an open circuit on the plus conductor, the only message displayed is 'open circuit on the plus conductor', without an indication of its position of the break on the loop (see also 'Tips').
• For a loop with stub branches which because of a open circuit or short circuit on the line do not form part of a continuous circuit, the line tester cannot discover which stub end is the open loop rather than a stub. Open loops that are a consequence of a open circuit or short circuit on the line are therefore always shown as two stubs, if necessary with sub-stubs. If only the plus conductor is open circuit, the topology of the loop is detected correctly, but the position of the open circuit on the line cannot be displayed (see also the previous point).
• 'DS11i Migration: Start Mixed Line Scan': A longer empty section of cable after the last detector on a stub can cause failure of the topology recognition.
• A short circuit to earth on the B-wire cannot then be localized in PC mode. Localization can be forced by taking the following steps:
• • Connect the A wire on the line tester to the ground conductor. The short circuit to earth on the B-wire then becomes a short circuit to the A wire.
  • Read the topology in once again. The defect location can be localized.
• Some power units supplied with FDUL221 respond to a short circuit by switching to FDnet/C-NET, thereby triggering a reset of the FDUL221, so that it fails to be read in. To remedy this, the batteries can be inserted even if the FDUL221 is being operated using the power unit.