Technical Library

Fault finding for Entryphone 9200 series audio door entry where residents cannot hear the visitor but the visitor can hear them. Terminal reference for the 92ETXAMP door board (D, C, E), the 95(V)RU relay unit and DA2H mains unit, the test order, reference readings and replacement parts.

How to test a ring final circuit in three steps: end-to-end, cross-connect line and neutral, cross-connect line and earth. What to expect and what the readings tell you.

The basic procedure for safely isolating a circuit or board before work or testing: identify, prove the tester, isolate, lock off, test dead in every combination, prove again.

The order of inspection and tests on a low voltage installation, with what each test is, how to carry it out and what to record. Dead tests first, then live tests.

What R1+R2 and bonding continuity should read for a given cable and length, why it matters, and how R1+R2 leads to the calculated earth fault loop impedance, Zs.