Abstract: To permit checking or testing the condition of a network which may carry integrated services digital, the test apparatus includes a switch which has gauged switch terminals (S, U) to operate the apparatus in selective modes. The apparatus, further, includes a local battery and a protective network (C5, 12, D1, D2, K, TF, I, II) included in circuit with test terminals (P+, P-). The switch connects the audio frequency generator to the test terminals, to the local battery, and to the local audio tone reproducer for continuity testing; if the protective circuit includes a transformer, a-c is prevented from reaching the network. In another mode, to test transmission of audio frequency through the test terminals into the network, the switch connects the audio frequency generator to the test terminals and to the local battery, to energize the audio frequency generator.

Abstract: An acoustic output electrical tester has externally accessible test terminals and internal test switches. The tester includes a multivibrator circuit which provides an output tone, the pitch of the tone, and its presence or absence, providing an indication with respect to the impedance, or transistor being tested. The externally accessible terminals can be selectively connected to a transistor, with the switching function replacing the externally connected transistor in the circuit of the multivibrator. A conductivity type reversal switch is provided to place the externally connected transistor in an internal circuit appropriate to the two conductivity types of the transistor.

Abstract: A local power source, such as a battery, is connected to a tone generator oscillator circuit which includes an audio reproducer. The tone generator includes a voltage sensing element such as a dark-resistance photoconductor, a resistor, or a Zener diode, at which the voltage is sensed when connected in a phase sequence circuit network or other network to be tested. The output tone, whether present or not, is indicative of a predetermined phase sequence of connection of test terminals. A transfer switch can connect the oscillator directly or through dropping resistors or non-linear resistances such as a Zener diode to the test terimals so that the test terminals can also be used to test for external resistance, short circuits, or polarity of applied voltages in the network which, depending on their polarity, may introduce external voltages, thus modifying the tone of oscillation of the tone generator.