Richardson's handbook of projection (1930)

1356 HANDBOOK OF PROJECTION FOR or in the switch itself. The ground can probably be located now by close inspection, though it may become necessary to unsolder the wire at the switch and again test the wire and the blade of the switch separately. No reading from ground to either of the wires shows this part O. K. Move the switch to disc. A reading from ground to one of the wires indicates a ground in the switching panel, the wire going to the reproducer, or the one going to the equalizer panel. The wires from the reproducer and from the equalizer come together in the switching panel. They can be separated here and tested individually. An open circuit in the wiring between the reproducer and the film disc transfer switch is easier to locate. When testing across the reproducer with the phones, sound is heard. Obviously, a record must be played while making the test. Testing with the phones at the input to the fader, no sound will be heard. Inspect and clean the contacts on the blades of the film disc switch, also the two switches at the top of the fader. A test with the phones at the input to the film disc switch will indicate whether the trouble is between this point and the reproducer or between here and the fader. If the trouble is in the line from the pick-up to the switch, test each of the two wires for continuity, using battery and voltmeter or battery and buzzer. If you use the battery and buzzer, be sure the reproducer is disconnected from the circuit, so as to eliminate the possibility of sending a current through it that might tend to demagnetize the permanent magnet. The circuit from the transfer switch to the fader can be tested in a similar manner, but in this case it is best to use a battery and a buzzer. The buzzer is used in